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Recent progress of III-V quantum dot infrared photodetectors on silicon
Abstract
Heterogeneous integration of III-V photodetectors on Si substrates offers great advantages for manufacturing complementary metal-oxide semiconductor (CMOS) compatible photonic components. However, the significant material lattice mismatch and thermal expansion co-efficient difference between III-Vs and Si materials present many challeges for heteroepitaxial growth. Quantum dots (QDs), due to the unique nature of three-dimensional quantum confinement as well as the defect tolerance, have now been emerging as a strong competitor to III-V quantum wells (QWs) and group IV counterparts. In this review, the recent progress on heterogeneous integration of III-V quantum dot infrared photodetectors (QDIPs) on Si substrates is summarized, focusing on direct epitaxial growth and bonding techniques on Si platforms over the last few years. At last, this review compares device performance of QDs to Ge and III-V bulk on Si substrates, illustrating the promising advantage of using QDs active regions towards efficient, high-density and low-cost on-chip photonics.
... Nanotechnology has emerged as a groundbreaking field with diverse applications across various disciplines [1]. Among the nanoscale materials, quantum dots (QDs) hold a special place due to their unique properties [1][2][3][4][5][6][7][8][9][10][11][12]. The convergence of physics, materials science, chemistry, and biotechnology at the nanoscale has paved the way for the creation of novel materials exhibiting properties markedly different from their bulk counterparts [1][2][3][4][5][6][7][8]. ...
... Among the nanoscale materials, quantum dots (QDs) hold a special place due to their unique properties [1][2][3][4][5][6][7][8][9][10][11][12]. The convergence of physics, materials science, chemistry, and biotechnology at the nanoscale has paved the way for the creation of novel materials exhibiting properties markedly different from their bulk counterparts [1][2][3][4][5][6][7][8]. ...
... In physics and material science, QDs primarily explore the behavior of electrons and photons at the nanoscale, whereas in chemistry, this they are associated with colloids, micelles, polymer composites, and similar structures [1][2][3][4][5][6][7][8][9][10][11][12]. The interdisciplinary nature of nanotechnology allows for the manipulation and design of materials at the atomic and molecular levels, opening new possibilities in fields such as information technology, environmental science, medicine, food safety, agriculture, and more [4][5][6][7][8][9][10][11][12]. ...
A set of polymer-embedded, two-colored nanocomposites were prepared where the co-existing emission peaks (~578 nm and ~650 nm) had different ratios at their emission thresholds. The nanocomposite samples were simultaneously excited by a 405 nm laser, and the growth of photoluminescence intensities was studied as a function of excitation intensity. The two peaks showed different growth evolution mechanisms. The factors impacting this difference could be (1) energy transfer between the two sized nanoparticles; (2) relaxation mechanism of smaller nanoparticles; and (3) material properties of the polymer.
... "Types of Photodetectors:") utilizing novel and bio medically safe QDs [44,45]. Ren et al. [46] developed Quantum Dot (QD)-based nano-photodetector by integrating the traditional III-V semiconductors. A few other review articles point out that PbS QDs have shown the most promising nanomaterials for the use of commercial NIR detection mainly due to their immense amount of light absorption, and lowcost of the material involved ( Fig. 4) [47][48][49]. ...
... Results in a device with high detectivity and sensitivity [46] 4 Organic Photo-diode (OPD) ...
This review article focuses on the role of nanotechnology (NT) in the development of advanced organic and inorganic photodetectors and their potential applications in the coming decades. We initiate the article with an overview of NT and potential applications of Nanotechnology in the twenty-first century ranging from Semiconductor manufacturing to Medical Imaging to Renewable energy to Quantum computing to Opto-electronics. The second part of the article delved into specific details on the role of nanotechnology and nanomaterials in developing advanced Photodetectors (PDs) and specifically discussing the internal functioning of near-infrared (NIR) photodetectors. Subsequently we focused on the performance metrics of PDs and types of PDs namely Organic Photodetectors (OPD) and Inorganic Photodetectors (IPD). We continued our in-depth discussion on OPDs and IPDs elaborating their structural features, operation mechanisms, types, performance optimization and role of functional nanomaterials. The final part of this review focuses on key applications of photodetectors e.g., retinal implant, biomedical imaging, personalized health monitoring, telecommunication, and military applications etc. Finally, we concluded the review paper discussing future opportunities and challenges regarding applications of NIR photodetectors in the twenty-first century.
Graphical Abstract
... In order to characterize the performance of photodetectors and compare different kinds of PD, some key figure-of-merit parameters are typically used. The main ones are summarized below [25,26]: ...
... As well know, the interaction between light and matter strongly depends by the photon energy and the band structure of the material constituent the photodetector. Then, effects of the light-matter interaction exploited for the photon-carrier transduction in PDs are summarized as following [25][26][27]: ...
With the aim to take advantage from the existing technologies in microelectronics, photodetectors should be realized with materials compatible with them ensuring, at the same time, good performance. Although great efforts are made to search for new materials that can enhance performance, photodetector (PD) based on them results often expensive and difficult to integrate with standard technologies for microelectronics. For this reason, the group IV semiconductors, which are currently the main materials for electronic and optoelectronic devices fabrication, are here reviewed for their applications in light sensing. Moreover, as new materials compatible with existing manufacturing technologies, PD based on colloidal semiconductor are revised. This work is particularly focused on developments in this area over the past 5-10 years, thus drawing a line for future research.
... Meanwhile, perovskite QDs and PbS QDs have been applied for visible [6,7] and NIR photodetection [8,9] owing to their high absorption coefficients. Additionally, HgX (X = S, Se, or Te), Ag 2 Se, and III-V semiconductor (e.g., InAs and GaAs) QDs have been applied for short-wave IR (SWIR: 1.5-2.5 µm), mid-wave IR (MWIR: 3-5 µm), and long-wave IR (LWIR: 8-12 µm) detection, respectively [10,11]. For detecting high-energy radiations such as X-rays and γ-rays, Pb (Z = 82) and Bi (Z = 83) QDs with high atomic numbers and high densities have been explored. ...
... During the last decades, different materials and device structures have been suggested for LWIR detectors [3]. Today, the most common planar material structures include HgCdTe (MCT) [4], and quantum structures including InAs/GaSb type-II superlattices [5], quantum wells (QWs) [6] and quantum dots (QDs) [7]. ...
Here we report on an experimental and theoretical investigation of the long-wavelength (LWIR) infrared photoresponse of photodetectors based on arrays of three million InP nanowires with axially embedded InAsP quantum discs. An ultra-thin top ITO contact combined with a novel photogating mechanism facilitates an improved LWIR normal incidence sensitivity in contrast to traditional planar quantum well photodetectors. The electronic structure of the quantum discs, including strain and defect-induced photogating effects, and optical transition matrix elements were calculated by an 8-band k·p simulation along with solving drift-diffusion equations to unravel the physics behind the generation of narrow linewidth intersubband signals observed from the quantum discs.
... Semiconductor quantum dots (QDs) with free carriers confined by three dimensions in space have physical properties similar to the atomic system. Modifying the electrical and optical properties of QDs by manipulating their shape, size, or composition to meet the specific needs of devices such as field effect transistors, lasers, detectors, memories, and intermediate band solar cells (IBSCs) is a fascinating challenge [1][2][3][4][5][6][7][8][9][10][11]. InAs/GaAs 1−x Sb x QDs grown in Stranski-Krastanow * Authors to whom any correspondence should be addressed. ...
Understanding the electrical and optical properties of InAs/GaAs(Sb) quantum dots (QDs) is essential for designing and improving the performance of related semiconductor QD devices. In this paper, the effects of In segregation, QD size, capping layer thickness and Sb composition on the electrical and optical properties of type I and type II InAs/GaAs1-xSbx (0≤x≤1) QDs are systematically investigated and general regularities are summarized. The comparisons of electron distribution probabilities, interband and intraband transition energies and absorption coefficients show that In segregation and QD size have a strong influence on the electron energy level positions of InAs QDs and that the trade-offs between absorption peak energy, absorption intensity and radiative lifetime of InAs/GaAs1-xSbx QDs can be optimized by adjusting the thickness and Sb composition of the GaAs1-xSbx capping layer. The results obtained are promising for the applications in the pre-design and performance feedback of the QD devices such as QD lasers, QD infrared detectors and intermediate band solar cells.
... As it is possible to grow them onto substrates with slightly different lattice constants, this strain results in controlled deformations across the crystal structure [36]. Some of the key advantages of this development are: bandgap engineering, enabling precise tailoring of the material's response to different infrared wavelengths, optimal designing of infrared detectors, photodetectors, and imaging sensors operating optimally within specific infrared ranges [37,38]. The ability to control lateral strain provides a powerful tool for designing advanced infrared light sources with tailored emission characteristics. ...
In\(_x\)Ga\(_{1-x}\)As\(_y\)Sb\(_{1-y}\) epilayers with a fixed In content of \(\textit{x}\) = 0.145 were grown on GaSb(100) substrates using liquid-phase epitaxy (LPE). The lattice mismatch between the quaternary epilayers and substrates was analyzed for different As contents (\(\textit{y}\)) by X-ray \(\omega\)-2\(\theta\). Epilayers with As content between \(\textit{y}\) = 0.120 and \(\textit{y}\) = 0.124 exhibited a positive lattice mismatch, leading to compressive strain. These samples showed a high crystalline quality and flat surfaces, as confirmed by high-resolution X-ray diffraction (HR-XRD) and atomic force microscopy (AFM). Quaternary alloys with As content between \(\textit{y}\) = 0.133 and \(\textit{y}\) = 0.141 displayed a negative lattice mismatch, resulting in tensile strain. Structural defects in these samples were evidenced by HR-XRD and on AFM micrographs. Raman measurements also revealed that lateral strain has a direct impact on the intensities of the LO-like, phonon–plasmon and disorder-activated longitudinal acoustic modes. For all In\(_x\)Ga\(_{1-x}\)As\(_y\)Sb\(_{1-y}\) films, photoluminescence (PL) spectra showed a bound exciton (BE) transition, with additional features observed in samples under tensile strain, indicating the involvement of native defect centers and donor–acceptor pairs. This study provides new insights into the effect of lateral strain on the crystalline and surface quality, and optical properties of quaternary alloys, relevant for novel optoelectronic applications.
... ZnO Nanowires CVD >10 G Ω 1-5 orders lower [195] Nanowires Vapor phase transport process 3.5 M Ω-cm 4-6 orders lower [196] Nanowires CVD 1-10 nA 100 μA [197] Nanowires MOCVD ~110 μA ~170 μA [198] Nanowire film Sol-gel method 4.32 x 10 -9 A 5.11 x 10 -7 A [199] Nanowires Chapter: 2 Literature review: Chronological development of optoelectronic devices 25 Semiconductor quantum dots have emerged as a consequence of sustained downscaling approach enabling the transition of device dimensions from bulk to nanoscale. Last two decades have witnessed significant progress on the fabrication of semiconductor quantum dots for photodetecting applications due to its tunable energy band gap, high quantum efficiency, high operating temperature, reduced dark current and high detectivity [51,212,213]. Since the first report on inter sub-band transitions in quantum devices [214], significant efforts have been made for the fabrication of quantum dot based photodetectors to achieve superior performances. ...
The current research work encompasses design modelling and fabrication of vertically aligned nanowire metal oxide semiconductor based voltage tunable quantum dot devices for optoelectronic applications. A novel device scheme is proposed for developing such VTQDs by combining the effects of nanowire geometry dependent structural confinement in transverse directions and the voltage assisted surface quantization in longitudinal direction. The formation of VTQDs near oxide/semiconductor interface at room temperature is predicted by developing a self consistent quantum electrostatic simultaneous solver. The photogeneration phenomenon and carrier transport in nanowire MOS based VTQD devices is analytically modelled by adopting non equilibrium Greens formalism based on second quantization field operators for incident photons and generated photocarriers. Engineering the combined effects of structural and electrical quantization has enabled a route for developing wavelength selective direct colour sensors with high spectral resolution. The developed NEGF based analytical model is further extended to obtain photocurrent which can be utilized for harvesting solar energy. A design window is also proposed for obtaining the desired values of solar cell performance parameters with the optimized device parameters such as, the nanowire diameter and oxide thickness. Finally, a patterned array of such nanowire MOS based VTQD devices is fabricated by employing electron beam lithography. The step like behaviour in capacitance voltage characteristics of such devices measured in situ within the FESEM chamber confirms the formation of VTQDs at room temperature. Such patterned nanowire MOS based VTQD devices can be utilized for the advanced photosensing and solar energy harvesting applications.
... Firstly, Ge is an indirect bandgap semiconductor with a relatively small absorption coefficient; secondly, the dark current of Ge PDs grown on Si is large due to the existing crystal defects and the inherent large thermionic emission coefficient [7]; thirdly, the absorption spectrum of Ge drops considerably beyond 1550 nm which precludes its application in longer wavelengths. In contrast, III-V PDs based on direct bandgap semiconductors feature large absorption coefficients, and the flexible band engineering of these binary, ternary, and quaternary compounds engenders a variety of high-performance PDs with operating wavelengths spanning from the near-infrared all the way to the mid-infrared band [12,13]. In addition, as the on-chip lasers of Si photonics The integration technologies of III-V lasers and PDs are quite similar. ...
An efficient photodetector (PD) is a key component in silicon-based photonic integrated circuits (PICs). III–V PDs with low dark current density, large bandwidth, and wide operation wavelength range have become increasingly important for Si photonics in various applications. Monolithic integration of III–V PDs on Si by direct heteroepitaxy exhibits the lowest cost, the largest integration density, and the highest throughput. As the research of integrating III–V lasers on Si flourishes in the last decade, various types of III–V PDs on Si with different device structures and absorption materials have also been developed. While the integration of III–V lasers on Si using various technologies has been systematically reviewed, there are few reviews of integrating III–V PDs on Si. In this article, we review the most recent advances in III–V PDs directly grown on Si using two different epitaxial techniques: blanket heteroepitaxy and selective heteroepitaxy.
... ZnO Nanowires CVD >10 G Ω 1-5 orders lower [195] Nanowires Vapor phase transport process 3.5 M Ω-cm 4-6 orders lower [196] Nanowires CVD 1-10 nA 100 μA [197] Nanowires MOCVD ~110 μA ~170 μA [198] Nanowire film Sol-gel method 4.32 x 10 -9 A 5.11 x 10 -7 A [199] Nanowires Chapter: 2 Literature review: Chronological development of optoelectronic devices 25 Semiconductor quantum dots have emerged as a consequence of sustained downscaling approach enabling the transition of device dimensions from bulk to nanoscale. Last two decades have witnessed significant progress on the fabrication of semiconductor quantum dots for photodetecting applications due to its tunable energy band gap, high quantum efficiency, high operating temperature, reduced dark current and high detectivity [51,212,213]. Since the first report on inter sub-band transitions in quantum devices [214], significant efforts have been made for the fabrication of quantum dot based photodetectors to achieve superior performances. ...
The current research work encompasses design modelling and fabrication of vertically aligned nanowire metal oxide semiconductor based voltage tunable quantum dot devices for optoelectronic applications. A novel device scheme is proposed for developing such VTQDs by combining the effects of nanowire geometry dependent structural confinement in transverse directions and the voltage assisted surface quantization in longitudinal direction. The formation of VTQDs near oxide/semiconductor interface at room temperature is predicted by developing a self consistent quantum electrostatic simultaneous solver. The photogeneration phenomenon and carrier transport in nanowire MOS based VTQD devices is analytically modelled by adopting non equilibrium Greens formalism based on second quantization field operators for incident photons and generated photocarriers. Engineering the combined effects of structural and electrical quantization has enabled a route for developing wavelength selective direct colour sensors with high spectral resolution. The developed NEGF based analytical model is further extended to obtain photocurrent which can be utilized for harvesting solar energy. A design window is also proposed for obtaining the desired values of solar cell performance parameters with the optimized device parameters such as, the nanowire diameter and oxide thickness. Finally, a patterned array of such nanowire MOS based VTQD devices is fabricated by employing electron beam lithography. The step like behaviour in capacitance voltage characteristics of such devices measured in situ within the FESEM chamber confirms the formation of VTQDs at room temperature. Such patterned nanowire MOS based VTQD devices can be utilized for the advanced photosensing and solar energy harvesting applications.
... Having a III-V on Si platform then leads to a more expensive fabrication and limits its use in low cost high volume applications. To integrate III-V materials there are a few methods available to bond the material to the substrate i.e., flipchip bonding, heterogeneous bonding and hetero-epitaxial growth(68). ...
Silicon (Si) photonics as a field is about photonic integrated circuits (PIC) using group IV materials as a substrate, mainly Si. Creating PICs from Si allows circuitry to be small and inexpensive; enabled by the use of mature fabrication techniques, existing recipes and foundries. The small size of PICs is useful for applications such as free-space telecommunication and chemical sensing where many devices are needed or are made as consumables. An infrared photodetector that is responsive in the 3-4 µm is needed to create PICs for these applications (1). To keep the cost low, a detector should be monolithically grown or deposited on Si. Si defect mediated detectors have been shown to be responsive, up to wavelengths of 2.5 µm (2), and able to operate at high speeds (up to 35 GHz) (3), but have not yet demonstrated a spectral response in the 3-4 µm region. Defect mediated germanium (Ge) detectors are potential candidates for detecting 3-4 µm light. Ge can be epitaxially grown on Si and using it for defect mediated absorption currently is relatively unexplored. In this thesis, Ge PIN photodiodes were created and implanted with boron ions to create defects within a rib waveguide. The responsivity versus the length of the photodiode implanted with defeccts was investigated, at fluences of 1x1010, 1x1012 and 1x1014 ions/cm2 , using no reverse bias. These measurements showed that the boron implantation had a negative effect on the responsivity, although, the unimplanted detectors had an unexpectedly high responsivity of approximately 0.1 A/W. This prompted investigation into the responsivity with an increasing reverse bias using 2 µm and 3.8 µm light, which resulted in a maximum responsivity of 1.04 A/W at -10 V using 2 µm light and 0.1 A/W at -7 V using 3.8 µm light at room temperature. A 12.5 Gb/s pseudorandom pattern was used to modulate 2 µm light, the detection of this light resulted in an open eye diagram. Measurements were performed to find the photodetection method, the linearity of the devices suggested that there was no two photon absorption, there was minimal difference in transmission between waveguides and photodiodes suggesting that photoactive defects were not created in the PIN junction formation. Finally, Raman spectroscopy was performed and found a 0.22 % strain which may be responsible for most of the absorption at 2 µm. The absorption at 3.8 µm may be caused from threading dislocations at the Ge Si boundary as similar wafers showed a high density of defects at the boundary. These results show Ge-on-SOI as a practical detection material in an extended wavelength range. More research is needed to understand the source of infrared absorption
... The GaAs/AlGaAs-based QWIPs can be fabricated with sensitivity in the 6-20 μm range, but the spectral region will depend on the transitions allowed by the quantum-well configuration and may be relatively narrow. Quantum dot IR photodetectors (QDIPs) are also being investigated, and they may offer more performance enhancements, but research is still in the early stages [21]. ...
In the context of More than Moore (MtM), an overview is given of optical detectors that are either commercially available today or in advanced development. Focus is placed on the integration in or with complementary metal‐oxide‐semiconductor (CMOS) technology that can provide electronic readout circuits as well as circuits for signal amplification and speed enhancement. Today, optical detectors form part of optical sensors used in a wide range of technologies spanning the electromagnetic spectrum from well below vacuum‐ultraviolet wavelengths, through visual wavelengths to the far infrared ( FIR ). Mobile telecommunication has particularly pushed the development of potent CMOS imagers comprised of Si photodiode (PD) pixels, suitable for visual to near‐infrared wavelength detection, but many applications of the shorter ultraviolet wavelengths (e.g. monitoring/diagnostic systems in medicine, flame detection, radiation detection, and biosensors) and the longer infrared wavelengths (e.g. fiber optics, laser, remote sensing, data storage, and optical communication systems) are also under intensive development. The merging of CMOS electronics with photonic integrated circuit s ( PIC s) is now being enabled by high‐performance Ge‐on‐Si and InGaAs‐based photodiodes. Wide‐bandgap materials have been developed for solar‐blind ultraviolet detectors. Narrow‐bandgap photoconductors are suitable for infrared wavelengths up to about of 20 μm, beyond which thermal detectors are used. Alternative photodetector devices are being researched using special nanowire, quantum‐well/‐dot, and 2D‐material structures that additionally may have their performance enhanced by adding plasmonic surface structures. These technologies aim to enhance the compatibility with CMOS by enabling direct integration at the chip level, either as front‐end CMOS modules or as back‐end add‐ons.
... Their zero-dimensional structure makes them very promising due to their delta function type of density of states, stronger carrier localization, higher exciton binding energies, and superior oscillator strength [8,9]. Together with IV-VI QD semiconductors (such as tellurides [10,11], sulfides [12,13] and their variants [14,15]) III-V QDs are among the most interesting materials in solid state physics [16,17]. In particular, self-assembled InAs QDs epitaxially grown on GaAs (0 0 1) by the Stransky-Krastanov (SK) mode are potentially advantageous as active region in emitter devices such as single-photon sources or laser diodes, because their optimized height/diameter aspect ratio could provide deeper confinement of charge carriers, lower threshold currents, and greater temperature insensitivity compared to other nanostructures [18]. ...
The effect of a Bi supply on the development of InAs/GaAs (001) QDs has been structurally explored in two growth temperature regimes, one for Bi alloying (380 °C) and another for conventional formation of InAs QDs (510 °C). At high growth temperature (HT), there is no trace of Bi incorporation into the film and Bi acts as a surfactant limiting the diffusion length of In. All HT QDs are coherent and free of defects with an inverted cone-shaped In distribution. Increasing the Bi supply increases both the QD size and the In content (up to 40%), while decreasing their areal density. At low temperature (LT), the addition of Bi goes beyond the surfactant role, promoting the transformation of the growth mode from 2D to 3D, resulting in an exponential increase in the QD size with Bi supply. Based on size, these LT QDs are divided into two populations in which the larger QDs relax plastically through the formation of misfit dislocations. LT QDs grown under a Bi flux reach a higher In content (80 %) with a homogeneous distribution within them. Remarkably, incorporation of Bi into larger QDs has been detected but it is not homogeneously distributed.
... Photodetection in hybrid quantum dot structures can provide flexible optimization of spectral characteristics. A review article on quantum dot infrared photodetectors [40] provides an excellent summary of technologies, including hybrid QD detectors on silicon and silicon nitride. The two-dimensional materials similar to those seen in hybrid electro-absorption modulators can also be used as photodetectors. ...
While photonic integration has made remarkable progress in recent years, there is no one integrated photonic platform that offers all desired functionalities and manufacturability on the same platform. GaAs and InP-based optoelectronic integrated circuits (OEICs) were very popular in the past decades; however, silicon photonics has recently emerged as a preferred platform due to its high-density and high-yield manufacturability leveraging the CMOS ecosystem, although it lacks optical gain, the Pockels effect, and other characteristics. On the other hand, hybrid photonic integration adds new and diverse functionalities to the host materials like silicon. This opinion paper investigates hybrid integrated photonic platforms, and discusses the new functionalities added to the silicon CMOS photonic platform.
... It is well known that the properties of materials, especially in the development of systems based on thin films, are affected by the parameters and effects of synthesis, such as magnetic and electric fields, surface interactions, and annealing processes, among other procedures performed after their manufacture. 1,2 Annealing processes in situ and after sample preparation or devices based on thin films significantly influence the properties that govern the material and make it relevant to its specific application. ...
This work presents a study of the morphological and structural properties of GaSb and GaSb/Mn thin films as support for the construction of GaSb/Mn multilayer systems deposited on Si (001) wafer substrate for electronic and spintronic applications. Thin films were obtained through DC magnetron sputtering, and the GaSb thin film was subjected to high-vacuum annealing for 2 h, 4 h, 6 h, 8 h and 10 h. The morphological properties were studied by SEM micrographs. It was observed that the width of depression regions on the GaSb thin film surface decreased (from ~ 617 nm to ~ 56 nm) when the annealing time was increased. A fast Fourier transform filter allowed identifying the formation of grains on the surface of the sample. The dependence of the grain size on the annealing times was described through the abnormal model. XRD measurements and the Burke–Turnbull model were used for establishing the dependence between GaSb crystallite size and annealing times. From Auger spectra, it was possible to determine the Ga diffusion process, its high mobility in the GaSb matrix, and its relationship with morphological properties. It was observed that the thermal processes favor the GaSb phase formation and the increase of grain size on the surface of the sample. AFM micrographs showed the topographical characteristics of the GaSb thin films surface and MFM images presented an exploration of the magnetic behavior for the bilayer system. Loops in hysteresis at 50 K were observed through measurements of the vibrating sample magnetometer, for the GaSb/Mn3 sample fabricated at room temperature (Ts = 300 K). These loops have been attributed to the magnetic anisotropy conditions generate through unbalanced Mn magnetic moments due to the Mn antiferromagnetic property presented at this temperature and the diffuse interfaces between GaSb and Mn layers. Lastly, the study of morphological properties of single-layer GaSb and its dependence on annealing times allowed determining that GaSb/Mn multilayer systems fabricated at room temperature present diffuse interfaces, although with clearly distinguished layers, and represent an alternative option for their fabrication.
... The concepts and fundamental principles of LED links are illustrated in Box 1. Micro-LEDs (µLEDs) based on crystalline inorganic III-V semiconductors have been widely examined for communications 2 . Because of advances in epitaxy, lithography and flip-chip techniques 6 , III-V µLEDs have delivered a modulation bandwidth from several hundred megahertz to over one gigahertz 2,7 . A non-polar m-plane InGaN/GaN µLED with a high modulation bandwidth of 1.5 GHz was demonstrated in 2018 7 , and a 1.3 GHz electrical-to-optical bandwidth quantum dot (QD) µLED was recently reported with a data rate of 4 Gbps (ref. ...
The continuing development of consumer electronics, mobile communications and advanced computing technologies has led to a rapid growth in data traffic, creating challenges for the communications industry. Light-emitting diode (LED)-based communication links are of potential use in both free space and optical interconnect applications, and LEDs based on emerging semiconductor materials, which can offer tunable optoelectronics properties and solution-processable manufacturing, are of particular interest in the development of next-generation data communications. Here we review the development of emerging LED materials—organic semiconductors, colloidal quantum dots and metal halide perovskites—for use in optical communications. We examine efforts to improve the modulation performance and device efficiency of these LEDs, and consider potential applications in on-chip interconnects and light fidelity (Li-Fi). We also explore the challenges that exist in developing practical high-speed LED-based data communication systems.
... {|φ n } is the corresponding orthonormal basis of H S . To advance further in computing the matrix elements, we apply the operation φ n | • |φ n on Equation (16) (where • represents the operator), and after this, we apply φ n | • |φ m on Equation (16). ...
This paper focuses on modeling a disordered system of quantum dots (QDs) by using complex networks with spatial and physical-based constraints. The first constraint is that, although QDs (=nodes) are randomly distributed in a metric space, they have to fulfill the condition that there is a minimum inter-dot distance that cannot be violated (to minimize electron localization). The second constraint arises from our process of weighted link formation, which is consistent with the laws of quantum physics and statistics: it not only takes into account the overlap integrals but also Boltzmann factors to include the fact that an electron can hop from one QD to another with a different energy level. Boltzmann factors and coherence naturally arise from the Lindblad master equation. The weighted adjacency matrix leads to a Laplacian matrix and a time evolution operator that allows the computation of the electron probability distribution and quantum transport efficiency. The results suggest that there is an optimal inter-dot distance that helps reduce electron localization in QD clusters and make the wave function better extended. As a potential application, we provide recommendations for improving QD intermediate-band solar cells.
... Recently, interest on III-V PDs grown on Si started to flourish, complementing the research on integrating III-V lasers on Si and the eventual goal of having high-performance III-V photonics integrated on the Si-photonics platform. Blanket hetero-epitaxy of III-V PDs on Si yields extremely low dark currents [12][13][14][15][16]. However, the thick buffer layers for defect reduction make it challenging for light coupling with Si waveguides, and the 3 dB bandwidths of these PDs often fall in the range of sub-10 GHz. ...
Integrating light emission and detection functionalities using efficient III-V materials on Si wafers is highly desirable for Si-based photonic integrated circuits. To fulfill the need of high-performance photodetectors (PDs) monolithically integrated on Si for Si photonics, we demonstrate III-V PDs directly grown on a InP/Si-on-insulator (SOI) platform parallel to the Si device layer in a variety of device dimensions. Device characteristics including a 3 dB bandwidth beyond 40 GHz, open eye diagrams at 40 Gb/s, a dark current of 0.55 nA, a responsivity of 0.3 A/W at 1550 nm, and 0.8 A/W at 1310 nm together with a 410 nm operation wavelength span from 1240 nm to 1650 nm are achieved. We further simulate the feasibility of interfacing the III-V PDs with the Si waveguide by designing waveguide-coupled PDs with butt coupling schemes. These results point to a practical solution for the monolithic integration of III-V active components and Si-based passive devices on a InP/SOI platform in the future.
... Early QD sensors relied on InGaAs eQDs grown on InP, in which photoexcited electrons were emitted into the InP transport matrix with the help of an electric field (Fig. 4A) (75). eQD IR detectors were then considered a compelling sensing platform of IR light (76), demonstrating low dark current and high sensitivity and speed (77,78). ...
Advances in colloidal quantum dots
The confinement found in colloidal semiconductor quantum dots enables the design of materials with tunable properties. García de Arquer et al . review the recent advances in methods for synthesis and surface functionalization of quantum dots that enable fine tuning of their optical, chemical, and electrical properties. These important developments have driven the commercialization of display and lighting applications and provide promising developments in the related fields of lasing and sensing. —MSL
... So far, perhaps most of the QDIPs reported in the literature have been developed using III-V semiconductor QDs [18]. Though, QWIPs using II-VI material system with decent performance have been demonstrated recently [19,20], the behavior of QDIP based on II-VI QDs is mostly unknown. ...
In this work, the impact of the quantum dot parameters, including dot size, and material composition on the optoelectronic performance of quantum dot infrared photodetectors (QDIPs) is systematically studied. The QDIP is based on the intra-valence band transitions in Zn1-xCdxSe QDs. The eigen energies and wavefunction of the hole states are computed under the framework of the multi-band k.p model. The obtained electronic structure is further utilized to calculate the dark current density, responsivity, and detectivity of QDIPs. An increase in CdSe content markedly reduces the dark current density as well as improves the responsivity. As a result, detectivity enhances significantly. Raising the QD size also brings enhancement in the detectivity. Moreover, peak response wavelength depends on the CdSe content and dot dimensions. These results might provide new directions for the development of p-type II-VI QDs based QDIP.
... Typically, state-of-the-art SWIR photodetectors are based on semiconductors with narrow band gaps, such as HgCdTe alloy [10], InSb [11], or quantum-well and quantum-dot structures on group III to V materials [12,13]. Despite the excellent performance and mature fabrication technology of these detectors, the material growth difficulties (lattice mismatch) and the sophisticated fabrication process requirements pose limits on the deployment of their applications [14,15]. ...
Layered two-dimensional (2D) materials with broadband photodetection capability have tremendous potential in the design and engineering of future optoelectronics devices. To date, studies of 2D semiconductors are actively focused on graphene, black phosphorus, and black arsenic phosphorus as attractive candidates. So far, however, novel group IV–V 2D semiconductors (e.g., GeAs and SiAs) have not been extensively explored for broad-band optoelectronics applications. Here, we report a high-performance multilayered 2D GeP gate-tunable photodetector that operates at a short-wavelength infrared (SWIR) regime. With a back-gate device geometry, a p-type behavior is observed at room temperature. Furthermore, a broadband spectral response from UV to optical communication wavelengths is detected. Under a nanowatt-level illumination, a peak responsivity of 25.5 A/W at λ = 1310 nm is achieved with detectivity of ∼ 1×10¹¹ cm.Hz1/2.W⁻¹ at a source−drain bias of −5 V and medium gate voltage bias of -30 V. Additionally, the devices show a relatively low dark current of 40-250 nA for device area in the range of 50-600 µm² and excellent stability and reproducibility. Our work demonstrates the potential of 2D GeP as an alternative mid-infrared material with broad optical tunability suitable for optical communication and low-light-level detection applications.
... Indium-based (nano)materials are of high technological significance in modern electronics. Representative devices incorporating indium are transparent conducting electrodes (indium tin oxide), [1] photodetectors (indium and indium gallium arsenide) [2] or phosphors (indium phosphide) as used e. g. in the last generation of TV screens. [3] The race toward miniaturization and the implementation of devices at nanoscale has spotlighted the question of an efficient synthesis protocol for nanoparticles (NPs). ...
The synthesis and characterization of the new compounds K(P3C2R2) [R=Ad (2), sBu (3)] and In(P3C2R2) [R=Ad (4), Mes (5)] are described. Further, the synthesis of indium nanoparticles via a single‐source precursor approach using In(1,2,4‐P3C2tBu2) (1) as precursor is reported. These nanoparticles were characterized by TEM, HRTEM, EDX, XRD, NMR, and optical spectroscopy.
... For instance, SAQD-based devices help achieve single-electron charge sensing [12], entanglement between spins and photons [13,14], single-photon sources [15], or single-spin [16], and help also the control of Cooper pair splitting [17], spin transport [18], spin-orbit interaction [19], g-factor [20], and Kondo effect [21]. On the other hand, SAQD technologies allow for manufacturing high density of QDs, which are crucial for implementing optoelectronic devices such as QD-based light-emitting diodes (LEDs) [22], QD-memories [4,23], QD-lasers [24][25][26][27], QD-infrared photodetectors [8,28,29], and QD-solar cells [30]. A key point in these devices is that the position of carrier level(s) can be tuned by controlling the dot size [2], and, this, by modifying the growth conditions [6,10,11,31]. ...
This paper focuses on modeling a disorder ensemble of quantum dots (QDs) as a special kind of Random Geometric Graphs (RGG) with weighted links. We compute any link weight as the overlap integral (or electron probability amplitude) between the QDs (=nodes) involved. This naturally leads to a weighted adjacency matrix, a Laplacian matrix, and a time evolution operator that have meaning in Quantum Mechanics. The model prohibits the existence of long-range links (shortcuts) between distant nodes because the electron cannot tunnel between two QDs that are too far away in the array. The spatial network generated by the proposed model captures inner properties of the QD system, which cannot be deduced from the simple interactions of their isolated components. It predicts the system quantum state, its time evolution, and the emergence of quantum transport when the network becomes connected.
... State-of-the-art infrared and broadband detectors are mostly based on semiconductors with narrow band gaps, such as HgCdTe alloy 6 , InSb 7 , or quantum-well and quantum-dot structures on group III to V materials 8,9 . However, these materials suffer from major challenges such as toxicity, growth difficulties (lattice mismatch) 10,11 , complex advanced fabrication processes requirements, and a low operating temperature that limits their wide applications. ...
Novel group IVV 2D semiconductors (e.g., GeAs and SiAs) has arisen as an attractive candidate for broad-band photodetection and optoelectronic applications. This 2D family has wide tunable bandgap, excellent thermodynamic stability, and strong in-plane anisotropy. However, their photonic and optoelectronic properties have not been extensively explored so far. In this work we demonstrate a broadband back-to-back metal-semiconductor-metal (MSM) Schottky photodiode with asymmetric contact geometries based on multilayered 2D GeAs. The photodetector exhibited a Schottky barrier height (SBH) in the range of 0.40 to 0.49 eV. Additionally, it showed low dark current of 1.8 nA with stable, reproducible, and excellent broadband spectral response from UV to optical communication wavelengths. The highest measured responsivity in the visible is 905 A/W at 660 nm wavelength and 98 A/W for 1064 nm near infrared. Most notably, the planner configuration of this GeAs photodetector showed low detector capacitance below 1.2 pf, low voltage operation (<1V), and a large bandwidth which may exceed 40 GHz. The stability and broadband response of the device are promising for this 2D materials application in high-speed optoelectronic devices.
A novel mechanism is proposed to overcome the band-gap variation with temperature in a hybrid quantum system, which is of a great significance in some advanced fields, such as atomic clocks of quantum sensing systems and optical communications.
The structural, electronic, and optical characteristics of cubic InP<sub>1-x</sub>Sb<sub>x</sub>(x = 0, 0.25, 0.50, 0.75, 1) ternary alloys were explored using the full-potential linearized augmented plane wave density functional theory approach. The total energy vs. volume optimization, lattice constants, and density of states were investigated for InP<sub>1-x</sub>Sb<sub>x</sub> alloys using exchange correlation function Wu-Cohen generalized gradient approximation (WC-GGA), available with the WIEN2k code. Band structure of the alloys was calculated using TB-mBJ functional to achieve a higher bandgap accuracy. The results of the mBJ experiment are in close agreement to those of the other experimental studies when compared to WC-GGA. Dielectric function and energy loss function were calculated in order to explore optical properties of the alloys. It was noticed that the estimated lattice parameters exhibit reduction when the Sb content is increased. Furthermore, the compositional dependency of the structural, electronic, and optical properties were also reported. For the InP<sub>1-x</sub>Sb<sub>x</sub> alloys, a band gap of less than 1.6 eVwere observed, making it suitable for usage in infrared optoelectronics devices.
Two-dimensional layered material/semiconductor heterostructures have emerged as a category of fascinating architectures for developing highly efficient and low-cost photodetection devices. Herein, we present the construction of a highly efficient flexible light detector operating in the visible-near infrared wavelength regime by integrating a PdTe 2 multilayer on a thin Si film. A representative device achieves a good photoresponse performance at zero bias including a sizeable current on/off ratio exceeding 10 ⁵ , a decent responsivity of ~343 mA/W, a respectable specific detectivity of ~2.56 × 10 ¹² Jones, and a rapid response time of 4.5/379 μ s, under 730 nm light irradiation. The detector also displays an outstanding long-term air stability and operational durability. In addition, thanks to the excellent flexibility, the device can retain its prominent photodetection performance at various bending radii of curvature and upon hundreds of bending tests. Furthermore, the large responsivity and rapid response speed endow the photodetector with the ability to accurately probe heart rate, suggesting a possible application in the area of flexible and wearable health monitoring.
Two-dimensional CuCrP2S6 possesses significant potential for low-power non-volatile devices owing to its multiferroic properties. Nonetheless, comprehensive investigations regarding the modulation of CuCrP2S6 polarization for enhancing semiconductor photodetection capabilities and its potential applications in ferroelectric non-volatile devices are still relatively scarce. In this study, we present a novel, non-volatile, tunable photodetector engineered through the integration of a ferroelectric heterostructure comprising CuCrP2S6 and InSe. Our findings reveal that distinct ferroelectric polarization states of CuCrP2S6 exert varying modulation effects on the InSe photodetection performance. Notably, optimized results give a responsivity of 1839 A W⁻¹ and a detectivity of 1.9 × 10¹² Jones at a 300 nm wavelength, featuring a substantial 20.7-fold difference in responsivity between the two polarization states. This investigation underscores the immense potential of CuCrP2S6 in the development of non-volatile, multi-state optoelectronic devices.
Silicon‐based optoelectronic devices, including silicon‐based lasers and silicon‐based photodetectors (PDs), are essential parts for silicon‐based optoelectronic integration. With the advancement of material epitaxy technologies such as metal–organic chemical vapor phase epitaxy (MOCVD) and molecular beam epitaxy (MBE), it has become possible to integrate III–V semiconductor optoelectronic devices, especially by monolithic growth, with low‐cost and large‐sized silicon substrates. However, the differences in material properties such as lattice constant, polarity, and thermal expansion coefficient between III–V materials and silicon lead to tremendous challenges in monolithic growth. In recent years, the unique three‐dimensional quantum confinement and defect insensitivity characteristics of quantum dots have greatly improved the performance of optoelectronic devices. This article reviews recent research progress in monolithic growth and optoelectronic devices of III–V semiconductor materials on silicon substrates, emphasizing the development of silicon‐based quantum dot optoelectronic devices.
2D materials have manifested themselves as key components toward compact integrated circuits. Because of their capability to circumvent the diffraction limit, light manipulation using surface plasmon polaritons (SPPs) is highly‐valued. In this study, plasmonic photodetection using graphene as a 2D material is investigated. Non‐scattering near‐field detection of SPPs is implemented via monolayer graphene stacked under an SPP waveguide with a symmetric antenna. Energy conversion between radiation power and electrical signals is utilized for the photovoltaic and photoconductive processes of the gold‐graphene interface and biased electrodes, measuring a maximum photoresponsivity of 29.2 mA W⁻¹. The generated photocurrent is altered under the polarization state of the input light, producing a 400% contrast between the maximum and minimum signals. This result is universally applicable to all on‐chip optoelectronic circuits.
This study probes the extent to which dislocations reduce carrier lifetimes and alter growth morphology and luminescence in InAs quantum dots (QD) grown on silicon. These heterostructures are key ingredients to achieving a highly reliable monolithically integrated light source on silicon necessary for photonic‐integrated circuits. Around 20%–30% shorter carrier lifetimes are found at spatially resolved individual dislocations at room temperature using time‐resolved cathodoluminescence spectroscopy, highlighting the strong nonradiative impact of dislocations even against the three‐dimensional confinement of QDs. Beyond these direct effects of increased nonradiative recombination, it is found that misfit dislocations in the defect filter layers employed during III–V/Si growth alter the QD growth environment to induce a crosshatch‐like variation in QD emission color and intensity when the filter layer is positioned sufficiently close to the QD emitter layer. Sessile threading dislocations generate even more egregious hillock defects that also reduce emission intensities by altering layer thicknesses, as measured by transmission electron microscopy and atom probe tomography. This work presents a more complete picture of the impacts of dislocations relevant to the development of light sources for scalable silicon photonic integrated circuits.
Although perovskite nanocrystals have attracted considerable interests as emerging semiconductors in optoelectronic devices, design and fabrication of a deformable structure with high stability and flexibility while meeting the charge transport requirements remain a huge challenge. Herein, a combined soft‐hard strategy is demonstrated to fabricate intrinsically flexible all‐inorganic perovskite layers for photodetection via ligand cross‐linking. Perfluorodecyltrichlorosilane (FDTS) is employed as the capping ligand and passivating agent bound to the CsPbBr3 surface via Pb‐F and Br‐F interactions. The SiCl head groups of FDTS are hydrolyzed to produce SiOH groups which subsequently condense to form the SiOSi network. The CsPbBr3@FDTS nanocrystals (NCs) are monodispersed cubes with an average particle size of 13.03 nm and exhibit excellent optical stability. Furthermore, the residual hydroxyl groups on the surface of the CsPbBr3@FDTS render the NCs tightly packed and cross‐linked to each other to form a dense and elastic CsPbBr3@FDTS film with soft and hard components. The photodetector based on the flexible CsPbBr3@FDTS film exhibits outstanding mechanical flexibility and robust stability after 5000 bending cycles.
Flexible photodetectors (PDs) comprised of low-dimensional organic-inorganic hybrid perovskites having perovskite quantum dots are the next generation wearable optoelectronic devices. Here, a flexible Vis-NIR PD is designed containing 2D DJ perovskite (4AMP)(MA)2Pb3I10 (4AMP = 4-(aminomethyl)piperidinium, MA = methylammonium) (n3) and the micro concentration of CsPbI3 perovskite quantum dots (QDs) layered heterostructures. The device response under 660 nm light is increased to 615% controlled by the optimal concentration of QDs. The device combination as per the mass of QDs depicts strong photosensitivity and high-power output. The band gap between the two is minimal forming a matching structure which lowers the energy barrier of carrier transport process. QDs layer fills the gap of perovskite film forming an almost defect-free heterostructure. QDs layer isolates water and passivates the perovskite layer for the high-performance of optoelectronic devices. The degradation of PDs with the optimal concentration of QDs under up to 5000 bending cycles and different bending angles can be ignored, and the devices show a self-healing phenomenon with the increase of bending cycles. The optimized strategy will develop flexible, wearable, high-performance and low-cost PDs.
InP/ZnS core/shell quantum dots have shown extraordinary application potential in photocatalysis. In this work, we demonstrated by ultrafast spectroscopy that the electron transfer ability of InP/ZnSe/ZnS core/shell/shell quantum dots was better than that of InP/ZnS quantum dots, because the introduction of ZnSe midshell resulted in improved passivation and greater exciton delocalization. The temperature-dependent PL spectra indicate that the exciton-phonon coupling strength and exciton binding energy of InP/ZnSe/ZnS quantum dots are smaller than those of InP/ZnS quantum dots. Further photocatalytic hydrogen evolution testing revealed that the photocatalytic activity of InP/ZnSe/ZnS quantum dots was significantly higher than that of InP/ZnS quantum dots, and InP/ZnSe/ZnS quantum dots even demonstrated improved stability. This research deepened our understanding of carrier dynamics and charge separation of InP/ZnSe/ZnS quantum dots, especially highlighting the application potential of InP/ZnSe/ZnS quantum dots in photocatalytic hydrogen evolution.
In recent decades, quantum dots (QDs) with tunable band gap, large absorption
coefficient, high quantum yield, multi-exciton effect, and easy solution processing
have unparalleled advantages in photoelectric conversion. Due to rapid rise of
performance indicators, quantum dot-based photoelectronic devices are advancing
towards commercialization. However, there is still a lack of reviews on the synthesis,
composition, structure, and photoelectronic applications, and also rarely referring to
photocatalysis. First, this review almost completely summarizes advantages and
disadvantages of common synthesis methods for QDs, especially pointing out the
importance of optimization strategies for preparing high-quality QDs such as ligand
engineering, ion exchange, and purification separation. Then, while introducing the
photoelectronic properties of perovskite quantum dots (PQDs) and carbon quantum
dots (CDs), we also focus on the development of different semiconductor quantum
dots (SQDs) composition. Next, the strengths and weaknesses of the four structures of
quantum dots are compared in detail. Finally, We separately demonstrate the
flourishing development in various photoelectronic applications, and compare
development level of SQDs, PQDs and CDs to discover the most suitable application
scenarios for each. On these basis, we also put forward bottlenecks and opportunities,
hoping to stimulate more breakthroughs in this field.
Flexible electronics have drawn great attentions from both academic researchers and industrial practitioners, due to their wide applications in military, medical, industrial, consumer electronics and others. Inorganic nanomaterials are of great interest as the functional materials for constructing high‐performance and reliable flexible electronic devices. In this chapter, we review the recent development in this area, with a focus on the fundamentals and applications. This chapter begins with the materials strategies of flexible electronics, followed by the mechanical designs and assembly techniques for inorganic nanomembranes. Then, various types of flexible devices with different functionalities are summarized, and several system‐level demonstration examples including flexible imaging systems, epidermal electronics for human health monitoring, bioimplantable electronics for sensing, and power supply systems are reviewed. Finally, this chapter concludes with the summary of current challenges and perspectives of this field, which provides possible future directions across the fundamental studies and practical applications.
Recently, nanoscale light manipulation using surface plasmon polaritons (SPPs) has received considerable research attention. The conventional method of detecting SPPs is through light scattering or using bulky Si or Ge photodetectors. However, these bulky systems limit the application of nanophotonic circuits. In this study, the light-matter interaction between graphene and SPP was investigated. For realizing an improved integration in nanocircuits, single-layer graphene was added to asymmetric SPP nanoantenna arrays for nonscattering detection in the near field. The developed device is capable of detecting the controlled propagation of SPPs with a photoresponsivity of 15 mA/W, which paves the way for the new-generation on-chip optical communication.
Efficient charge transfer is closely related to improvement of the performance of quantum dot (QD)-based solar cells. In this paper, the effects of surface ligands with different alkyl chain lengths ((1-dodecanethiol (DDT) and 1-octanethiol (OT)) on the electron transfer process in InP/ZnS QDs were studied by ultrafast spectroscopy. With adsorption of the electron acceptor anthraquinone (AQ), both hot electron transfer and band-edge electron transfer between the QDs and acceptor were observed. The analysis shows that there is a more efficient (hot) electron transfer process in shorter-chain ligand OT-capped QDs compared with DDT-capped QDs, which is probably because of the improved passivation and lower density of trap states for OT-capped QDs in which electron trapping may compete with electron transfer and reduce the efficiency of electron transfer. This work enhances the understanding of how the chain length of ligands affects the electron transfer process from the perspective of ultrafast photophysical properties, and it may provide valuable insight into how to improve the performance of optoelectronic devices through surface-ligand engineering.
Quantum dot capped with a strain reducing layer is a fast-growing technology suitable for infrared photodetector. In general, capping layer used in such structure enriches dot region confinement and redshift of the emitted radiation. In this paper, a virtual GaAs1−xPx is used as a capping layer. The strain profile, photoluminescence peak and rate of carrier escape out of the quantum dot inside the proposed structure are thoroughly investigated. The fractional composition of P is varied from 0.1 to 0.6 and a corresponding shifting of photoluminescence peak from 1176 nm to 1137 nm is observed. The thermal emission rate equal to 1.599 x 10¹⁰ s⁻¹ and 6.437 1 x 10⁸ s⁻¹ for electron and hole respectively are observed for the proposed structure. A two-dimensional strain matrix evaluated for the mentioned range of P composition exhibits smoother normalization of compressive strain inside the capping layer as compared to GaAs0.86Sb0.14 capped device. Moreover, the effect of capping layer thickness on the strain profile, photoluminescence peak and carrier escape rate are investigated. The results of this analysis concludes that GaAs1−xPx is a useful candidate for the capping layer in quantum dot photodetector application.
A novel CQD-hybridized NiO x HTL is developed to improve the efficiency and stability of planar p–i–n PSCs.
Photodetectors on Si with high responsivity, large bandwidth, and multispectral operation are required for high data rate communications using Si photonics. We report characteristics of InP-based quantum dash (QDash) photodetectors with a p-i-n structure directly grown on (001) Si. Three layers of quantum dashes were grown on InP on Si templates and fabricated into waveguide photodetectors. The QDash photodetectors can operate from 1240 nm to 1640 nm, covering the entire telecommunication band. A low dark current density of 2.1 × 10⁻⁶ A/cm², responsivities of 0.35 ± 0.05 A/W at 1550 nm and 0.94 ± 0.05 A/W at 1310 nm, and a 3-dB bandwidth of 10.3 GHz were demonstrated. Our results show that the QDash photodetectors grown on Si hold great potential for on-chip integration in Si-photonics.
Direct growth of III-V infrared photodetectors on silicon substrates is a promising so- lution for realising low-cost and large-format infrared focal plane arrays. However, this heteroepitaxial growth technique will generate various defects due to the dissimilarities between III-V materials and Si. These defects can severely damage the performance of a detector. In this thesis, different III-V quantum structured infrared photodetectors directly grown on Si are investigated to understand how different structures react to the defects. The experimental chapters begin with reporting an InGaAs/GaAs quantum dot infrared pho- todetector (QDIP) on Si. By utilising a Si substrate with a high degree of offcut along with dislocation filter layers, antiphase domains have been eliminated and the threading dislocation density has been reduced by ∼4 orders of magnitude. The QDIP shows a dual-band photoresponse at 80 K. To reduce the noise, a sub-monolayer QD quantum cascade photodetector on Si was designed. This structure has led to a distinct reduction of dark current and noise, achieving a high operating temperature of 160 K. To further boost the quantum efficiency of infrared photodetectors on Si, InAs/GaSb type-II superlattice (T2SL) photodetectors were also studied in this thesis. Generally, T2SL photodiode structures are more sensitive to material defects than QDs. Moreover, the surface leakage current contributes to a high level of dark current. InAs/GaSb T2SL photodiodes and barrier detectors have been grown on GaAs and Si substrates. Transmission electron microscopy and X-ray diffraction results confirm that the strain energy has been released at the heteroepitaxy interface and the threading dislocation density has been reduced by ∼3 orders of magnitude. The bulk dark current has been reduced by implementing an nBp barrier design. As a result, a T2SL nBp detector on GaAs with surface passivation has been shown to be capable of operating at 190 K without external bias. The work described in this thesis shows that there is great potential to improve the detector performance by using novel detector designs. Future work should focus on structure optimisation, as well as material quality im- provements, in order to achieve both low dark current and high quantum efficiency. High- operating temperature detectors on Si can be attempted to further explore the potential of III-V quantum structured infrared photodetectors. Specific recommendations are made for candidate structures. In order to be compatible with the mainstream Si micro-electronics industry, fabrication on (001) Si substrates will be required. Research towards this objec- tive is therefore also proposed.
Urgent requirements for high-efficiency and low-cost photovoltaic devices are constantly pushing forward the development of the emerging solar cells. Currently, organic solar cells (OSCs) and perovskites solar cells (PSCs) were considerable as the most likely commercialized solar cells in the short-term period. Enormous optimization strategies towards optimizing the devices efficiency and stability have been developed. It is noteworthy that the well-known small-sized quantum dots (QDs), have been explored as the additional components in OSCs and PSCs, and yielded the rather modest amelioration of devices performance. Herein, we reviewed the recent advances in strategically integrating all kinds of QDs (consisting of metal chalcogenides based QDs, perovskite QDs, InP based QDs, carbon QDs, graphene QDs, black phosphorus QDs, and other emerging two-dimensional QDs) in association with relevant performance enhancement of OSCs and PSCs. In view of each type of QDs, we mainly emphasized their involved devices configuration, integration location, and physical mechanism. Additionally, the fundamental structures, operation principles and analogies/distinctions of OSCs and PSCs were briefly outlined. Finally, the existing challenges and future prospect based on QDs integrated OSCs and PSCs were listed out.
Miniaturized spectrometers offering low cost, low reagent consumption, high throughput, sensitivity and automation are the future of sensing and have significant applications in environmental monitoring and food safety, biotechnology, pharmaceuticals and healthcare. Mid-infrared (MIR) spectroscopy employing complementary metal oxide semiconductor (CMOS) compatible thin film waveguides and microfluidics shows great promise towards highly integrated and robust detection tools and liquid handling. This perspective provides an overview of emergence of thin film optical waveguides used for evanescent field sensing of liquid chemical and biological samples for MIR absorption spectroscopy. The state of the art of new material and waveguide systems used for spectroscopic measurements in MIR is presented. An outlook on the advantages and future of waveguide-based MIR spectroscopy for application in clinical settings for point-of-care biochemical analysis is discussed.
Solution-processed materials, including halide perovskites and newly discovered MXenes, are emerging as promising candidates for next-generation optoelectronic devices. Here, large-scale image sensor arrays (1250 pixels) based on a MXene/perovskite/MXene structure are demonstrated by utilizing top-down techniques, i.e. spin-coating and laser-scribing. The work allows processing perovskite and MXene materials into sub-millimeter photodetector arrays in large scale with potential for further down-scaling of device dimension. The favorable energy level alignment and resonance enhancement of such materials enable efficient charge transfer and detection up to near infrared region. A high responsivity of 84.77 AW⁻¹, a high specific detectivity of 3.22×10¹² Jones, and a large linear dynamic range (LDR) up to 82 dB in a broadband wavelength ranging from visible to near-infrared are achieved. In addition, the device shows an excellent image-capture capability under near infrared illumination. Given the tunability and compatibility with complementary metal-oxide-semiconductors (CMOS), the method potentially promotes the development of low-cost, high-performance, and large format photodetector arrays.
Silicon photonics provides a promising platform for energy-efficient interconnects within supercomputers and data centers. However, developing a complementary metal–oxide–semiconductor compatible high-speed photodetector with low dark current has long presented a challenge in the field. In this paper, we report the first O-band InAs quantum dot (QD) waveguide photodiode (PD) heterogeneously integrated on silicon. Record low dark currents as low as 0.01 nA, responsivities of 0.34 A/W at 1310 nm and 0.9 A/W at 1280 nm, and a record high 3 dB bandwidth of 15 GHz was measured. Avalanche gain was observed and a maximum gain of up to 45 and a gain bandwidth product (GBP) of 240 GHz were achieved, which are also record high results for any QD avalanche photodetector (APD) on silicon. Additionally, we demonstrate a device sensitivity of − 11 dBm at 10 Gb/s and open-eye diagrams up to 12.5 Gb/s. These QD-based PDs are able to operate as p-i-n PDs or APDs under different bias conditions and offer a promising alternative to heterogeneous InGaAs-on-silicon and SiGe counterparts in low-power optical communication links. They also leverage the same epitaxial layers and processing steps as heterogeneously integrated QD lasers, significantly simplifying the processing and reducing the cost of a fully integrated QD transceiver on silicon.
In this paper, the microcavity effect in quantum dot infrared photodetectors (QDIPs) on a Si substrate, fabricated by means of metal wafer bonding (MWB) and epitaxial lift-off (ELO) processes, was demonstrated by comparing the photocurrent spectrum and the simulated absorption spectrum. Four QDIPs having a different cavity length of 1.7 μm, 2.8 μm, 3 μm and 3.4 μm were fabricated and compared with simulation based on the finite-difference time-domain method. The resonance peaks were observed in both photocurrent spectrum and absorption spectrum due to the microcavity formed by the bottom mirror of Pt/Au layer and the flat GaAs/air interface. The peak wavelength of the photocurrent spectrum in all four QDIPs on Si samples shows a good agreement with the simulated absorption spectrum. The bias-dependent photocurrent was also measured to study the microcavity effects more in depth. The ratio of the increased photocurrent under bias condition shows higher value in the microcavity QDIPs, showing that the microcavity contributes to generate photocurrent effectively. From these results, we believe that the MWB and ELO could be useful to make the microcavity in many integrated chemical and bio sensing application.
We demonstrate 10 Gbit/s operation of InAs/InGaAs quantum dot (QD) p-i-n photodiodes (PDs) grown on on-axis (001) GaP/Si substrates. A 3.0 × 50 μm² QD PD shows a small dark current of 0.2 nA at a bias voltage of −3 V, which corresponds to a dark current density of 0.13 mA/cm². This low-dark current characteristic obtained from a narrow-stripe device indicates that sidewall and threading dislocations have small effects on the dark current. The 3 dB bandwidth was 5.5 GHz at a bias voltage of −5 V. Large signal measurement with non-return-to-zero signals shows 10 Gbit/s eye opening.
An InGaAs quantum dot (QD) photodetector is directly grown on a silicon substrate. GaAs-on-Si virtual substrates with a defect density in the order of 10⁶ cm⁻² are fabricated by using strained-layer superlattice as dislocation filters. As a result of the high quality virtual substrate, fabrication of QD layer with good structural properties has been achieved, as evidenced by transmission electron microscopy and x-ray diffraction measurements. The InGaAs QD infrared photodetector is then fabricated on the GaAs-on-Si wafer substrate. Dual-band photoresponse is observed at 80 K with two response peaks around 6 and 15 μm.
Top-illuminated PIN and modified uni-traveling carrier (MUTC) photodiodes based on InGaAs/InAlAs/InP were epitaxially grown on Si templates. Photodiodes with 30-μm diameter have dark currents as low as 10 nA at 3 V corresponding to a dark current density of only 0.8 mA/cm². The responsivity, 3-dB bandwidth, output power and third-order output intercept point (OIP3) were 0.79 A/W, 9 GHz, 2.6 dBm and 15 dBm, respectively.
Direct epitaxial integration of III-V materials on Si offers substantial manufacturing cost and scalability advantages over heterogeneous integration. The challenge is that epitaxial growth introduces high densities of crystalline defects that limit device performance and lifetime. Quantum dot lasers, amplifiers, modulators, and photodetectors epitaxially grown on Si are showing promise for achieving low-cost, scalable integration with silicon photonics. The unique electrical confinement properties of quantum dots provide reduced sensitivity to the crystalline defects that result from III-V/Si growth, while their unique gain dynamics show promise for improved performance and new functionalities relative to their quantum well counterparts in many devices. Clear advantages for using quantum dot active layers for lasers and amplifiers on and off Si have already been demonstrated, and results for quantum dot based photodetectors and modulators look promising. Laser performance on Si is improving rapidly with continuous-wave threshold currents below 1 mA, injection efficiencies of 87%, and output powers of 175 mW at 20 °C. 1500-h reliability tests at 35 °C showed an extrapolated mean-time-to-failure of more than ten million hours. This represents a significant stride toward efficient, scalable, and reliable III-V lasers on on-axis Si substrates for photonic integrate circuits that are fully compatible with complementary metal-oxide-semiconductor (CMOS) foundries.
We report InAs/InGaAs quantum dot (QD) waveguide photodetectors (PD) monolithically grown on silicon substrates. A high-crystalline quality GaAs-on-Si template was achieved by aspect ratio trapping together with the combined effects of cyclic thermal annealing and strain-balancing layer stacks. An ultra-low dark current of 0.8 nA and an internal responsivity of 0.9 A/W were measured in the O band. We also report, to the best of our knowledge, the first characterization of high-speed performance and the first demonstration of the on-chip photodetection for this QD-on-silicon system. The monolithically integrated waveguide PD shares the same platform as the previously demonstrated micro-ring lasers and can thus be integrated with laser sources for power monitors or amplifiers for pre-amplified receivers.
As a promising integration platform, silicon photonics need on-chip laser sources that dramatically improve capability, while trimming size and power dissipation in a cost-effective way for volume manufacturability. Currently, direct heteroepitaxial growth of III–V laser structures on Si using quantum dots as the active region is a vibrant field of research, with the potential to demonstrate low-cost, high-yield, long-lifetime, and high-temperature devices. Ongoing work is being conducted to reduce the power consumption, maximize the operating temperature, and switch from miscut Si substrates toward the so-called exact (001) Si substrates that are standard in microelectronics fabrication. Here, we demonstrate record-small electrically pumped micro-lasers epitaxially grown on industry standard (001) silicon substrates. Continuous-wave lasing up to 100°C was demonstrated at 1.3 μm communication wavelength. A submilliamp threshold of 0.6 mA was achieved for a micro-laser with a radius of 5 μm. The thresholds and footprints are orders of magnitude smaller than those previously reported lasers epitaxially grown on Si.
We report the fabrication of quantum dot infrared photodetectors (QDIPs) on silicon (Si) substrates by means of metal wafer bonding and an epitaxial lift-off process. According to the photoluminescence (PL) and x-ray diffraction measurements, the QDIP layer was transferred onto the Si substrate without degradation of the crystal quality or residual strain. In addition, from the PL results, we found that an optical cavity was formed because Pt/Au of the bonding material was served as the back mirror and the facet of the GaAs/air was served as the front mirror. The device performance capabilities were directly compared and peak responsivity was enhanced by nearly twofold from 0.038 A/W to 0.067 A/W.
High performance III-V lasers at datacom and telecom wavelengths on on-axis (001) Si are needed for scalable datacenter interconnect technologies. We demonstrate electrically injected quantum dot lasers grown on on-axis (001) Si patterned with {111} v-grooves lying in the [110] direction. No additional Ge buffers or substrate miscut was used. The active region consists of five InAs/InGaAs dot-in-a-well layers. We achieve continuous wave lasing with thresholds as low as 36 mA and operation up to 80°C.
We demonstrate the first electrically pumped continuous-wave (CW) III–V semiconductor lasers epitaxially grown on on-axis (001) silicon substrates without offcut or germanium layers, using InAs/GaAs quantum dots as the active region and an intermediate GaP buffer between the silicon and device layers. Broad-area lasers with uncoated facets achieve room-temperature lasing with threshold current densities around 860 A / cm 2 and 110 mW of single-facet output power for the same device. Ridge lasers designed for low threshold operations show maximum lasing temperatures up to 90°C and thresholds down to 30 mA.
The integration of III-V on silicon is still a hot topic as it will open up a way to co-integrate Si CMOS logic with photonic devices. To reach this aim, several hurdles should be solved, and more particularly the generation of antiphase boundaries (APBs) at the III-V/Si(001) interface. Density functional theory (DFT) has been used to demonstrate the existence of a double-layer steps on nominal Si(001) which is formed during annealing under proper hydrogen chemical potential. This phenomenon could be explained by the formation of dimer vacancy lines which could be responsible for the preferential and selective etching of one type of step leading to the double step surface creation. To check this hypothesis, different experiments have been carried in an industrial 300 mm metalorganic chemical vapor deposition where the total pressure during the annealing step of Si(001) surface has been varied. Under optimized conditions, an APBs-free GaAs layer was grown on a nominal Si(001) surface paving the way for III-V integration on silicon industrial platform.
Reliable, efficient electrically pumped silicon-based lasers would enable full integration of photonic and electronic circuits, but have previously only been realized by wafer bonding. Here, we demonstrate continuous-wave InAs/GaAs quantum dot lasers directly grown on silicon substrates with a low threshold current density of 62.5 €...A €...cm -2, a room-temperature output power exceeding 105 €...mW and operation up to 120 €...°C. Over 3,100 €...h of continuous-wave operating data have been collected, giving an extrapolated mean time to failure of over 100,158 €...h. The realization of high-performance quantum dot lasers on silicon is due to the achievement of a low density of threading dislocations on the order of 10 5 €...cm 2 in the III-V epilayers by combining a nucleation layer and dislocation filter layers with in situ thermal annealing. These results are a major advance towards reliable and cost-effective silicon-based photonic-electronic integration.
We demonstrate a 67 GHz bandwidth silicon-contacted germanium waveguide p-i-n photodetector operating at −1 V with 6.8 fF capacitance. The dark current is below 4 nA. The responsivity is 0.74 A/W at 1550 nm and 0.93 A/W at 1310 nm wavelength. 56 Gbps on-off-keying data reception is demonstrated with clear open eye diagrams in both the C-band and O-band.
Cross section transmission electron microscopy has been used to analyse dislocation filter layers (DFLs) in five similar structures of GaAs on Si that had different amounts of strain in the DFLs or different annealing regimes. By counting threading dislocation (TD) numbers through the structure we are able to measure relative changes, even though the absolute density is not known. The DFLs remove more than 90% of TDs in all samples. We find that the TD density in material without DFLs decays as the inverse of the square root of the layer thickness, and that DFLs at the top of the structure are considerably more efficient than those at the bottom. This indicates that the interaction radius, the distance that TDs must approach to meet and annihilate, is dependent upon the TD density.
We report self-assembled InAs/GaAs quantum dots
(QDs)
grown on a specially engineered GaAs-on-V-grooved-Si substrate by metal-organic vapor phase epitaxy. Recessed pockets formed on V-groove patterned Si (001) substrates were used to prevent most of the hetero-interfacial stacking faults from extending into the upper QD active region. 1.3 μm room temperature emission from high-density (5.6 × 1010 cm−2) QDs has been obtained, with a narrow full-width-at-half-maximum of 29 meV. Optical quality of the QDs was found to be better than those grown on conventional planar offcut Si templates, as indicated by temperature-dependent photoluminescence analysis. Results suggest great potential to integrate QD lasers on a Si complementary-metal-oxide-semiconductor compatible platform using such GaAs on Si templates.
Nanometre-scale semiconductor devices have been envisioned as next-generation technologies with high integration and functionality. Quantum dots, or the so-called ‘artificial atoms’, exhibit unique properties due to their quantum confinement in all 3D. These unique properties have brought to light the great potential of quantum dots in optoelectronic applications. Numerous efforts worldwide have been devoted to these promising nanomaterials for next-generation optoelectronic devices, such as lasers, photodetectors, amplifiers, and solar cells, with the emphasis on improving performance and
functionality. Through the development in optoelectronic devices based on quantum dots over the last two decades, quantum dot devices with exceptional performance surpassing previous devices are evidenced. This review describes recent developments in quantum dot optoelectronic devices over the last few years. The paper will highlight the major progress made in 1.3 μm quantum dot lasers, quantum dot infrared photodetectors, and quantum dot solar cells.
We review recent advances in the field of quantum dot lasers on silicon. A summary of device performance, reliability, and comparison with similar quantum well lasers grown on silicon will be presented. We consider the possibility of scalable, low size, weight, and power nanolasers grown on silicon enabled by quantum dot active regions for future short-reach silicon photonics interconnects.
In 1959, Lawson and co-workers published the paper which triggered development of variable band gap Hg1−xCdxTe (HgCdTe) alloys providing an unprecedented degree of freedom in infrared detector design. HgCdTe ternary alloy has been used for realization of detectors operating under various modalities including: photoconductor, photodiode, and metal-insulator-semiconductor detector designs. Over the last five decades, this material system has successfully overcome the challenges from other material systems. It is important to notice that none of these competitors can compete in terms of fundamental properties. The competition may represent more mature technology but not higher performance or, with the exception of thermal detectors, higher operating temperatures (HOTs) for ultimate performance. In the last two decades, several new concepts for improvement of the performance of photodetectors have been proposed. These new concepts are particularly addressing the drive towards the so called HOT detectors aiming to increase detector operating temperatures. In this paper, new strategies in photodetector designs are reviewed, including barrier detectors, unipolar barrier photodiodes, multistage detectors and trapping detectors. Some of these new solutions have emerged as a real competitor to HgCdTe photodetectors.
The realization of semiconductor laser diodes on Si substrates would permit the creation of complex optoelectronic circuits, enabling chip-to-chip and system-to-system optical communications. Direct epitaxial growth of III-V semiconductor materials on Si or Ge is one of the most promising candidates for the fabrication of electrically pumped light sources on a Si platform. Here, we describe the first quantum-dot laser to be realized on a Ge substrate. To fabricate the laser, a single-domain GaAs buffer layer was first grown on the Ge substrate using the Ga prelayer technique. A long-wavelength InAs/GaAs quantum-dot structure was then fabricated on the high-quality GaAs buffer layer. Lasing at a wavelength of 1,305 nm with a low threshold current density of 55.2 A cm-2 was observed under continuous-wave current drive at room temperature. The results suggest that long-wavelength InAs/GaAs quantum-dot lasers on Si substrates may be realized by epitaxial growth on Ge-on-Si substrates.
We report the growth of self-assembled InAs/GaAs quantum dots (QDs) on germanium-on-insulator-on-silicon (GeOI) substrate by metal organic chemical vapor deposition. We demonstrate that the introduction of a single QD layer can act as an anti-phase-domain filter resulting in GaAs/GeOI layers with high structural quality and low surface roughness. High density (4×1010 cm−2) QDs were obtained with emission at 1.3 μm, narrow peak linewidth (33 meV), and identical photoluminescence intensity at room temperature similar to QDs obtained on conventional GaAs substrate. These results show the feasibility of the GeOI platform for the monolithic integration of QD-based lasers on silicon.
A ten-stacked self-assembled InAs/GaAs quantum-dot infrared photodetector operated in the 2.5–7 μm range by photovoltaic and photoconductive mixed-mode near-room-temperature operation (⩾250 K) was demonstrated. The specific peak detectivity D∗ is 2.4×108 cm Hz1/2/W at 250 K. The use of high-band-gap Al0.3Ga0.7As barriers at both sides of the InAs quantum-dot structure and the long carrier recombination time are the key factors responsible for its near-room-temperature operation. © 2001 American Institute of Physics.
Self-assembled strained semiconductor nanostructures have been grown on GaAs substrates to fabricate quantum dot infrared photodetectors. State-filling photoluminescence experiments have been used to probe the zero-dimensional states and revealed four atomic-like shells (s,p,d,f) with an excitonic intersublevel energy spacing which was adjusted to ∼60 meV. The lower electronic shells were populated with carriers by n doping the heterostructure, and transitions from the occupied quantum dot states to the wetting layer or to the continuum states resulted in infrared photodetection. We demonstrate broadband normal-incidence detection with a responsivity of a few hundred mA/W at a detection wavelength of ∼5 μm. © 2001 American Institute of Physics.
Antiphase boundaries free GaSb epitaxial layers with low surface roughness (< 0.5 nm) have been synthesized on standard microelectronic 300 mm nominal (001)-Si substrates by metal organic chemical vapor deposition using a two-step growth process. By adjusting the growth temperature and the thickness of the nucleation layer, antiphase boundary free GaSb layers as thin as 250 nm are obtained. The 12% lattice mismatch between GaSb and Si is accommodated by both the formation of threading dislocations and a periodic array of 90° misfit dislocations at the interface. A GaSb layer inserted between AlSb barriers has been grown on an optimized GaSb/(001)-Si buffer layer and exhibits room temperature photoluminescence.
We demonstrate highly efficient, low threshold InAs quantum dot lasers epitaxially grown on on-axis (001) GaP/Si substrates using molecular beam epitaxy. Electron channeling contrast imaging measurements show a threading dislocation density of 7.3 × 10⁶ cm⁻² from an optimized GaAs template grown on GaP/Si. The high-quality GaAs templates enable as-cleaved quantum dot lasers to achieve a room-temperature continuous-wave (CW) threshold current of 9.5 mA, a threshold current density as low as 132 A/cm², a single-side output power of 175 mW, and a wall-plug-efficiency of 38.4% at room temperature. As-cleaved QD lasers show ground-state CW lasing up to 80 °C. The application of a 95% high-reflectivity coating on one laser facet results in a CW threshold current of 6.7 mA, which is a record-low value for any kind of Fabry-Perot laser grown on Si.
Investigations of antimonide-based materials began at about the same time as HgCdTe ternary alloys—in the 1950s, and the apparent rapid success of their technology, especially low-dimensional solids, depends on the previous five decades of III-V materials and device research. However, the sophisticated physics associated with the antimonide-based bandgap engineering concept started at the beginning of 1990s gave a new impact and interest in development of infrared detector structures within academic and national laboratories. The development of InAs/GaSb type-II superlattices (T2SLs) results from two primary motivations: the perceived challenges of reproducibly fabricating high-operability HgCdTe focal plane arrays (FPAs) at reasonable cost and the theoretical predictions of lower Auger recombination for type T2SL detectors compared with HgCdTe. Second motivation—lower Auger recombination should be translated into a fundamental advantage for T2SL over HgCdTe in terms of lower dark current and/or higher operating temperature, provided other parameters such as Shockley-Read-Hall (SRH) lifetime are equal. InAs/GaSb T2SL photodetectors offer similar performance to HgCdTe at an equivalent cut-off wavelength, but with a sizeable penalty in operating temperature, due to the inherent difference in SRH lifetimes. It is predicted that since the future infrared (IR) systems will be based on the room temperature operation of depletion-current limited arrays with pixel densities that are fully consistent with background- and diffraction-limited performance due to the system optics, the material system with long SRH lifetime will be required. Since T2SLs are very much resisted in attempts to improve its SRH lifetime, currently the only material that meets this requirement is HgCdTe. Due to less ionic chemical bonding, III-V semiconductors are more robust than their II-VI counterparts. As a result, III-V-based FPAs excel in operability, spatial uniformity, temporal stability, scalability, producibility, and affordability—the so-called “ibility” advantages.
High-performance, multispectral, and large-format infrared focal plane arrays are the long-demanded third-generation infrared technique for hyperspectral imaging, infrared spectroscopy, and target identification. A promising solution is to monolithically integrate infrared photodetectors on a silicon platform, which offers not only low-cost but high-resolution focal plane arrays by taking advantage of the well-established Si-based readout integrated circuits. Here, we report the first InAs/GaAs quantum dot (QD) infrared photodetectors monolithically integrated on silicon substrates by molecular beam epitaxy. The III–V photodetectors are directly grown on silicon substrates by using a GaAs buffer, which reduces the threading dislocation density to ∼106 cm–2. The high-quality QDs grown on Si substrates have led to long photocarrier relaxation time and low dark current density. Mid-infrared photodetection up to ∼8 μm is also achieved at 80 K. This work demonstrates that III–V photodetectors can directly be integrated with silicon readout circuitry for realizing large-format focal plane arrays as well as mid-infrared photonics in silicon.
This paper discusses key issues related to the quantum dot infrared photodetector (QDIP). These are the normal incidence response, the dark current, and the responsivity and detectivity. We attempt to address the following questions of what is QDIP's potential, what is lacking, and what is needed to make the device interesting for practical applications. It is argued that so far the present QDIP devices have not fully, demonstrated the potential advantages. Representative experimental results am compared with characteristics of quantum well infrared photodetectors. Areas that need improvements are pointed out.
Novel InAs/InGaAs quantum dots-in-a-well (DWELL) infrared photodetectors are reviewed. These detectors, in which the active region consists of InAs quantum dots (QDs) embedded in an InGaAs quantum well, represent a hybrid between a conventional quantum well infrared photodetector (QWIP) and a QD infrared photodetector (QDIP). Like QDIPs, DWELL detectors display normal incidence operation without gratings or optocouplers while demonstrating reproducible 'dial-in recipes' for control over the operating wavelength, like QWIPs. Using femtosecond spectroscopy, long carrier lifetimes have been observed in DWELL heterostructures, suggesting their potential for high temperature operation. Moreover, DWELL detectors have also demonstrated bias-tunability and multicolour operation in the mid-wave infrared (3-5 νm), long-wave infrared (LWIR, 8-12 νm) and very long-wave infrared (>14 νm) regimes. We have recently developed LWIR 320 × 256 focal plane arrays operating at liquid nitrogen temperatures. One of the potential problems with these detectors is the low quantum efficiency, which translates into low responsivity and detectivity. Some solutions for mitigating these problems are suggested at the end of this paper.
Based on the self-alignment principle, a new reflow flip-chip bonding technology for infrared detectors is proposed. By optimizing the dimensions between the under bump metallization (UBM) and the indium bump, 10 µm tall spherical indium balls are achieved firstly. Then the technical parameters of heating temperature and surface pre-treatment are discussed. Thereafter, a new reflow flip-chip bonding technology is applied to the infrared focal plane array (IRFPA) and it results in a 6.7% of the total bad pixel percentage which is dramatically decreased compared with the thermo-compression one of 41.9%. The deduced fatigue life of the IRFPA bonded by the new reflow flip-chip bonding technology is four times longer than that of the thermo-compression one.
For reasons associated with size, weight, power consumption, and cost, the future of infrared systems for all spectral bands is being driven towards megapixel formats operating under diffraction- and background-limited conditions with ever-smaller pixel pitches and ever-higher operating temperatures. The performance requirements of such systems with regard to both optical and detector limitations are examined for the materials technologies and device architectures that are in vogue today. At elevated operating temperatures, available noise equivalent temperature difference values for diffraction-limited operation are found to be strongly dependent on the available pixel pitch, optimizing at values ∼λ/4, where λ is the operating wavelength. The possibility for extending the operation of mid- and long-wavelength focal plane arrays to room temperature with diffraction- and background-limited performance is discussed, together with the potential issues that must be addressed in order to achieve this ultimate goal.
The thermally induced biaxial tensile stress in GaAs/Si is reduced by postgrowth patterning, and the reduction in stress is dependent on the pattern size and shape. For narrow stripe patterns the stress relief is obtained perpendicular to the stripe. For small square patterns the stress is relieved in both directions. Thermal cycle annealing is also effective in reducing the threading dislocations in GaAs/Si. A thermally cycle-annealed multi-quantum-well (MQW) laser on a Si substrate grown by metalorganic chemical vapor deposition has continuous threshold current as low as 24 mA at 300 K. Rapid degradation can be suppressed by postgrowth patterning for the thermally cycle-annealed laser with an 8-µm-wide stripe, which results from the reduction of the biaxial stress to the uniaxial stress.
A high performance bias-selectable mid-/long-wavelength infrared photodetector based on InAs/InAs1−x
Sb
x type-II superlattices on GaSb substrate has been demonstrated. The mid- and long-wavelength channels' 50% cut-off wavelengths were ∼5.1 and ∼9.5 μm at 77 K. The mid-wavelength channel exhibited a quantum efficiency of 45% at 100 mV bias voltage under front-side illumination and without any anti-reflection coating. With a dark current density of 1 × 10−7 A/cm2 under 100 mV applied bias, the mid-wavelength channel exhibited a specific detectivity of 8.2 × 1012 cm·
Hz
/W at 77 K. The long-wavelength channel exhibited a quantum efficiency of 40%, a dark current density of 5.7 × 10−4 A/cm2 under −150 mV applied bias at 77 K, providing a specific detectivity value of 1.64 × 1011 cm·
Hz
/W.
InAs/GaAs quantum dot (QD) lasers on silicon-on-insulator substrates with Si rib structures are fabricated by metal-stripe wafer bonding, where the metal strips work not only as the bonding layer but also as electrodes. Our Fabry–Pérot lasers operate with a threshold current density of 520 ${rm A},{cdot }, {rm cm}^{-2}$ for the broad-area laser, and a threshold current of 110 mA for the ridge laser. The bonded lasers exhibit an InAs QD ground-state lasing at $1.3~mu text{m}$ at room temperature.
Quantum well infrared photodetectors (QWIPs) are known for their stability, high pixel-to-pixel uniformity, and high-pixel operability, which are essential for large area imaging arrays. In this paper, we discuss the initial demonstration of QWIP devices, and the many years of progress that propelled this technology toward the demonstration of large format focal plane arrays. In addition, we present some potential applications of this technology in science and medicine.
We present 1.3 μm InAs/GaAs quantum dot lasers on Si substrates
operating at high temperatures. Our lasers are fabricated through
epitaxial growth on GaAs substrates of the InAs/GaAs quantum dot laser
double heterostructure, and subsequent GaAs/Si wafer bonding and layer
transfer onto Si substrates. Both of the on-Si lasers by direct- and
metal-mediated bonding exhibit lasing temperatures over 100 °C.
Partial p-type doping in the InAs/GaAs quantum dot core layer is found
to significantly increase the characteristics temperature T0.
This result verifies the suitability of III--V quantum dot lasers as a
light source in Si photonic integrated circuits.
The realization of semiconductor lasers on Si substrates will enable the fabrication of complex optoelectronic circuits. This will permit the creation of the long-dreamed chip-to-chip and system-to-system optical interconnects. This paper reports recent developments in our work on InAs/GaAs quantum-dot (QD) lasers monolithically grown on Si, Ge, and Ge-on-Si (Ge/Si) substrates. A thin AlAs nucleation layer (NL) was first investigated for the growth of InAs/GaAs QDs on Si substrates. The AlAs NL enables more defects to be confined in the interface between the GaAs epitaxial layer and Si substrate, and hence leads to higher photoluminescence intensity for InAs/GaAs QDs. Room-temperature lasing at 1.29 μm with a threshold current density of 650 A/cm2 was demonstrated with the use of an AlAs NL. The growth of InAs/GaAs QDs on Ge and Ge/Si substrates was further studied. A low threshold current density of ~200 A/cm2 for 1-mm long QD lasers has been demonstrated for QD lasers grown on Ge substrates by using Ga prelayer technique. This growth technique has also been explored for Ge/Si substrates. Room-temperature lasing at 1.28 μm with threshold current density of ~164 A/cm2 and lasing operation up to 84°C has been demonstrated for a 3-mm long device.
We report on an interband cascade mid-wave infrared (MWIR) detector based on type-II InAs/GaSb/AlSb strained layer superlattices (T2SL). The reported device has a seven-stage cascade region, each segment containing a MWIR absorber region, a graded T2SL transport region, and an interband tunneling region. Above room temperature spectral response was observed, with a cutoff wavelength of 7 μm at 420 K. Detailed radiometric measurements yielded a Johnson noise limited detectivity of 3.0 × 1011 cmHz1/2W−1 (8.9 × 108 cmHz1/2W−1) and a dark current density of 3.6 × 10−7 A/cm−2 (7.3 × 10−3 A/cm−2) near zero bias with a 100% cutoff wavelength of 5.2 μm and 6.2 μm at 77 K (295 K), respectively, with an estimated 36.2% QE.
Design and characterization of a quantum dot quantum cascade detector for photovoltaic midwave infrared photodetection (λpeak = 5.5 μm) is demonstrated. The quantum cascade barrier region provides the internal electric field to transfer photoexcited electrons into quantum dots of the next stack, enabling zero bias operation. Increased carrier relaxation time for intersubband transitions in quantum dots provides a distinct advantage for the carrier transport. Responsivity of 10 mA/W and detectivity of 9 × 109 cm Hz1/2 W−1 at 77 K for f/2 optics has been obtained at zero bias. Dark current density is 6.5 × 10−7A cm−2, at 80 K at zero bias.
The relaxation oscillation (RO) parameters and modulation properties of quantum-dot lasers are investigated depending on effective charge carrier scattering lifetimes of the confined quantum-dot states. We find three dynamical regimes of the laser, characterized by the level of synchronization between carrier dynamics in quantum-dots and quantum-well. For scattering rates similar to the RO frequency, a strong damping is found. On either side of this regime, simulations show low RO damping and improved dynamical response. Depending on the regime, the modulation response differs from conventional analytical predictions. Our results suggest the possibility of tailoring quantum-dot laser dynamical behavior via bandstructure engineering.
AlGaAs/GaAs double heterostructure laser diodes have been fabricated on Si substrates using GaP/(GaP/GaAsP) superlattice/(GaAsP/GaAs) superlattice intermediate layers grown by metalorganic chemical vapor deposition. A threshold current density at 16.5 °C and a characteristic temperature T0 of 4.9 kA/cm2 and 179 K respectively have been obtained for the diode on Si substrate.
We propose a new MBE growth method for InSb microcrystals on CdTe which
has a nearly equal lattice constant to InSb. The average size of the
InSb microcrystals was about 150 nm × 200 nm × 70 nm. This
method is based on the Sb incorporation into In droplets and thought to
be useful for fabricating quantum well boxes.
In the epitaxial Lift-off (ELO) technique, where a GaAs device structure is Lifted off from a GaAs substrate using selective wet etching of an AlAs release layer, the etching rate of the AlAs layer is increased by a factor of similar to 8 by raising the etchant temperature to 40 degrees C and adding a surfactant and an antifoaming agent to the etching solution. The mechanism of the high-rate lift-off process is discussed based on the solubility and the diffusion coefficient of the etching product (H-2) in the etching solution. Photoluminescence measurement results show that the quality of the GaAs him is not degraded by the high-rate lift-off process. A high-rate lift-off technique for large-diameter wafers is proposed.
In this paper we discuss photocurrent measurements in normal incidence geometry performed on self-assembled Ge dots in Si. The “classical” detector concept with vertical photocurrent is compared to a new one which is based on in-plane photoconductivity and is only realizable with dots. The active region of the samples consists of ten layers of Ge dots formed by self-assembly in the Stranski-Krastanov growth mode with lateral dimensions of about 20 nm and a height of about 1.5 nm. The mid-infrared photocurrent measurements show the typical line shape of bound-to-continuum transitions. The responsivity of the lateral device of 10 mA/W is about twice that of the vertical structure, furthermore the peak maximum at 284 meV is shifted by about 40 meV towards smaller energies. This is explained using a model involving carrier transfer to the modulation doping layer.
High-speed normal-incidence p-i-n InGaAs photodetectors epitaxially grown on silicon substrates by metal–organic chemical vapor deposition has been demonstrated. The InGaAs active layer lattice-matched to InP was successfully grown on Si substrates employing metamorphic growth of InP and GaAs buffers with a two-step growth technique, in addition to cyclic thermal annealing and strain-balancing layer stacks. Circular devices with diameters ranging from 20 to 60 $\mu{\rm m}$ were fabricated. Dark current diminished and 3-dB bandwidth increased with a reduction of the device area. A dark current of 0.2 $\mu{\rm A}$ and a responsivity of 0.5 A/W at 1550 nm were measured at ${-}{\rm 1}~{\rm V}$ for a device 20 $\mu{\rm m}$ in diameter. This device exhibited an optical 3-dB bandwidth of 10 GHz at ${-}{\rm 5}~{\rm V}$. An open eye diagram at 10 Gb/s at a low reverse bias of 1 V was also demonstrated.
A Ge-on-Si photodetector grown on a thin buffer on top of a Si substrate is presented. The device exhibits a zero bias bandwidth of 3.2 GHz and a photoresponsivity of 104 mA/W for a wavelength of 1300 nm. Zero bias operation is proposed to minimize the influence of dark currents on the device performance. The photoresponsivity for wavelengths near the absorption edge of Ge exceeds the values expected from absorption data of unstrained Ge reported in the literature. The depletion characteristics of the device are extracted from S-parameter-measurements using a small-signal equivalent circuit. The bandwidth of the device is limited by the RC-time constant and can be further increased, if the defect density is reduced.