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(a) Laser emission spectra and (b) peak intensity and line width of the spectra as a function of pumping power density.
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In this letter, we report on deep UV laser emitting at 249 nm based on thin GaN quantum wells (QWs) by optical pumping at room temperature. The laser threshold was 190 kW/cm2 that is comparable to state-of-the-art AlGaN QW lasers at similar wavelengths. The laser structure was pseudomorphically grown on a c-plane sapphire substrate by metalorganic...
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Context 1
... optical polarizations were measured perpendicular to the c-axis by employing a GlanTaylor polarizer between the optical fiber and the laser facet. Figure 5a shows the PL spectra with various pumping power densities from 120 to 288 kW/cm 2 . The peak emission wavelength was 249 nm, and there was almost no wavelength shift between spontaneous and stimulated emissions, indicating the minimized QCSE, thanks to the thinness of the GaN QWs. ...
Context 2
... short wavelength of 249 nm, equivalent to the transition energy of 5.0 eV, suggests the extreme quantum confinement effect in the AlN/GaN QWs. The intensity versus the pumping power density (red squares) in Figure 5b demonstrated the lasing operation with a low threshold of 190 kW/cm 2 , comparable to the state-of-the-art DUV lasers based on AlGaN MQWs grown on sapphire and AlN substrates at similar wavelengths. 3,13,26 Such a threshold can be mostly attributed to the high material and interface quality, large quantum and optical confinement, and smooth cleaved facet. ...
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Citations
... The maximum and the minimum points of the blue loops are corresponding to the main peaks at 968 nm and 950 nm, respectively, while the maximum and the minimum points of the red loops are corresponding to the second peaks at 934 nm and 930 nm, respectively. The polarization degree ( ), which is defined as = (I TE − I TM )/(I TE + I TM ) [56,57], is 0.95 for the emissions from the pure well regions and 0.12 for the emissions from the well-wire hybrid regions. The smaller polarization degree of 0.12 indicates the better strain release inside the well-wire hybrid regions than in the pure well regions. ...
Although traditional quantum-confined nanostructures e.g. regular quantum wells or quantum dots have achieved huge success in the field of semiconductor lasers for past decades, these traditional nanostructures are encountering the difficulty of enhancing device performance to a higher level due to their inherent gain bottleneck. In this paper, we are proposing a new super-gain nanostructure based on self-assembled well-wire complex energy-band engineering with InGaAs-based materials to break through the existing bottleneck. The nanostructure is constructed by utilizing the special strain-driven indium (In)-segregation and the growth orientation-dependent on-GaAs multi-atomic step effects to achieve the distinguished ultra-wide and uniform super-gain spectra. The structural details and its luminescence mechanism are investigated by multiple measurement means and theoretical modeling. The polarized gain spectra with the max fluctuation of <3 cm ⁻¹ in 904 nm–998 nm for transverse electric (TE) mode and 904 nm–977 nm for transverse magnetic (TM) mode are simultaneously obtained with this nanostructure. It enables an ultra-low output power fluctuation of <0.7 dB and a nearly-constant threshold power throughout an ultra-wide wavelength range under a fixed injection level. It was difficult to realize these in the past. Therefore, the described super-gain nanostructure brings a brand-new chance of developing high performance of tunable laser diodes.
... Deep ultraviolet (UV) lasers with wavelengths shorter than 280 nm have found many promising applications in sterilization, communication, optical storage, spectral analysis, and biochemical detection [1][2][3]. Most studies on ultraviolet radiation concentrate more on pulse laser [4]. ...
This report is about a continuous wave (CW) deep ultraviolet laser operation at 273 nm by intracavity frequency doubling of laser diode pumped Pr3+ doped LiYF4 lasers. We use two 3 W InGaN laser diodes, one 3 mm long Pr3+:LiYF4 (Pr:YLF) crystal and one 5 mm long beta-barium-borate (BBO) crystal, coherent radiation with an output power of 128 mW at 273 nm was obtained with a 2.9% optical to optical conversion efficiency. To the best of our knowledge, this is the first report detailing a Pr:YLF laser that emits light at 273 nm.
... GaN etc), with typical emission wavelengths around UV-A regime. Note that the cutting-edge semiconductor technology has demonstrated that AlGaN quantum wells could achieve lasing in UV-C regime (~ 250 nm) [9]. To access shorter UV wavelength, a convenient method is to adopt nonlinear frequency conversion technique. ...
... This parameter is in the range of state-of-the-art of UV laser diodes based on an SCH (see Table 1 and Fig. 10). A reduction of N th can be obtained by modifying the structure to be specifically adapted for optical pumping, approaching the QWs to the surface [28][29][30]. However, such designs are not compatible with electron beam pumping. ...
We report net gain measurements at room temperature in Al0.07Ga0.93N/GaN 10-period multi-quantum well layers emitting at 367 nm, using the variable stripe length method. The separate confinement heterostructure was designed targeting electron-beam pumped lasing at 10 kV. The highest net gain value was 131 cm⁻¹, obtained at the maximum pumping power density of the experimental setup (743 kW/cm²). The net gain threshold was attained at 218 kW/cm² using 193 nm optical pumping. From these experiments, we predict an electron-beam-pumped lasing threshold of 370 kW/cm² at room temperature, which is compatible with the use of compact cathodes (e.g. carbon nanotubes). In some areas of the sample, we observed an anomalous amplification of the photoluminescence intensity that occurs for long stripe lengths (superior to 400 µm) and high pumping power (superior to 550 kW/cm²), leading to an overestimation of the net gain value. We attribute such a phenomenon to the optical feedback provided by the reflection from cracks, which were created during the epitaxial growth due to the strong lattice mismatch between different layers.
... 13) Furthermore, optoelectronic devices using the GaN/AlN quantum structure can improve the output power over 2 Watt, 14) and simultaneously offer a practical application potential in LED, LD, and narrow-band DUV detectors. 15,16) However, orbital and electronic properties in the GaN/AlN quantum structures are not yet fully understood and required an effective model to guide the optimal structure design. The published literature shows the p x , p y , and p z orbitals of AlGaN are sensitive to the quantum confinement direction. ...
This work used the first-principles simulations to investigate interactions between orbital and electronic properties in the GaNm/AlNn quantum structure. By rotating the quantum well plane 90˚ from the c-plane, we delineated responses including a uniform bond length, an equal charge distribution on both well sides, and orbital changes at the quantum level near the valence band maximum (from the degenerated px/py to the separated py and pz). The found responses would positively contribute to wavelength reduction, quantum efficiency, and surface-emitting geometry. The tunable bandgap enables the production of electro-optic devices of Al-rich AlGaN for DUV applications.
... Kobayashi et al. of Kyoto University, Japan, recently successfully developed a GaN quantum well with a single atomic layer, with a peak emission wavelength near 225 nm, and increased its EQE to 5% [43]. Similarly, the team of Li Xiaohang of King Abdullah University of Science and Technology in Saudi Arabia achieved a 249 nm UVC laser output by growing a four-atomic layer GaN well region and a six-atomic layer AlN barrier region [44]. ...
High-quality epitaxial layers are directly related to internal quantum efficiency. The methods used to design such epitaxial layers are reviewed in this article. The ultraviolet C (UVC) light-emitting diode (LED) epitaxial layer structure exhibits electron leakage; therefore, many research groups have proposed the design of blocking layers and carrier transportation to generate high electron–hole recombination rates. This also aids in increasing the internal quantum efficiency. The cap layer, p-GaN, exhibits high absorption in deep UV radiation; thus, a small thickness is usually chosen. Flip chip design is more popular for such devices in the UV band, and the main factors for consideration are light extraction and heat transportation. However, the choice of encapsulation materials is important, because unsuitable encapsulation materials will be degraded by ultraviolet light irradiation. A suitable package design can account for light extraction and heat transportation. Finally, an atomic layer deposition Al2O3 film has been proposed as a mesa passivation layer. It can provide a low reverse current leakage. Moreover, it can help increase the quantum efficiency, enhance the moisture resistance, and improve reliability. UVC LED applications can be used in sterilization, water purification, air purification, and medical and military fields.
... S EMICONDUCTOR lasers fabricated with wide band-gap III-nitrides have wide applications in optical communication system, high-density optical data storage, bio-medical imaging, laser display and so on [1]- [7]. Among these lasers, the ones using low dimensional quantum dots (QDs) [8] as active regions have several advantages over their higher dimensional counterparts (e.g., quantum wells), which include temperature insensitivity [8], [9], ultra low threshold densities [10] as well as low linewidth enhancement factors [11], [12]. ...
III-nitride quantum dot (QD) lasers have potential applications in visible light regime, yet one of its most important dynamic parameters, the linewidth enhancement factor (LEF), has been rarely studied. We studied the LEF of InGaN QD lasers with a comprehensive theory model and found that the LEF values of InGaN QD lasers can be smaller and more robust against inhomogeneous broadening than those of InGaAs QD lasers. In addition, the LEF improvement from quantum well to QD in III-nitride semiconductors is much larger than that in III-arsenide. It is believed that the large confinement energy in III-nitrides and atomic-like density of states of QDs contribute to these advantages of III-nitride QD lasers. Our results not only reveal the advantages of using III-nitride QD for high spectral purity, low-chirp laser applications, but also provide a general guideline for designing QD lasers with lower LEF values in various semiconductor materials.
... In addition to the reports on the GaN QW UV LEDs, the first DUV laser based on the GaN QWs have been demonstrated at 249 nm. 28 This wavelength is equal to the shortest wavelength of the AlGaN QW laser with the TE polarization on the sapphire substrate. 6 In this work, we have demonstrated lasing at 244.63 nm with TE polarization from the 3 ML GaN/AlN QWs grown by MOCVD on the sapphire substrate, a record short wavelength from the GaN/AlN QWs to date. ...
... The thickness of the GaN wells and the AlN barriers was estimated to be 3 and 5.5 MLs, respectively, according to the growth rate and the previous work. 28 The thicknesses of the wells and barriers were designed from the trade-off between the wavelength, quantum confinement, optical confinement, and light absorption of the optical pumping source by a 193 nm ArF excimer laser. The optical confinement of the 40 period GaN/AlN (3 MLs/5.5 MLs) QW laser was estimated to be 27.2% through calculation of the optical field distribution by the COMSOL Multiphase software package. ...
We have demonstrated a record short wavelength lasing at 244.63 nm with TE dominant polarization from GaN quantum wells (QWs) at room temperature (RT). The optical threshold of 310 kW/cm² is comparable to state-of-the-art AlGaN QW lasers at similar wavelengths. The sample was grown on the AlN/sapphire template pesudomorphically. X-ray diffraction (XRD) shows unambiguous higher-order satellite peaks indicating a sharp interface amid the active region. The excitonic localization was revealed and studied by the photoluminescence (PL) and time-resolved PL (TRPL) spectroscopy at temperatures ranging from 15 K to RT. At 15 K, the multiple-component PL decay curves with the decay time varying from 62.6 to 2.77 ns at different energies confirmed the localized excitons. The peak energy of the temperature-dependent PL spectra exhibited the “S-shape” behavior; and the weak exciton localization with a small localization energy of 14.3 meV was observed. Therefore, even in the low temperature region, the escape possibility of excitons increased as the temperature rose. As a result, the fwhm of the emission spectra changed significantly when the temperature was below 150 K. Above 150 K, the PL decay shape changed from the two-component exponential decay to the single exponential decay, indicating complete delocalization of excitons. The work demonstrates the weak localization and thus smooth interface in the GaN/AlN active region, which are desirable for DUV lasers operating at RT.
... Most of the above listed research reports are based on planar structures and have not addressed the quantification of TE and TM modes except for few of the reports. 27,30,32 Planar device structures are not the most efficient nanostructures to unleash the full potential of the quantum confinement. Moreover, native substrates are very expensive, and growing planar nanostructure on highly mismatched foreign substrates leads to a high concentration of threading dislocations, generating nonradiative recombination centers and resulting in a poor IQE and hence low external quantum efficiency. ...
Heavy reliance on extensively studied AlGaN based light emitting diodes (LEDs) to replace environmentally hazardous mercury based ultraviolet (UV) lamps is inevitable. However, external quantum efficiency (EQE) for AlGaN based deep UV emitters remains poor. Dislocation induced nonradiative recombination centers and poor electron-hole wavefunction overlap due to the large polarization field induced quantum confined stark effect (QCSE) in “Al” rich AlGaN are some of the key factors responsible for poor EQE. In addition, the transverse electric polarized light is extremely suppressed in “Al”-rich AlGaN quantum wells (QWs) because of the undesired crossing over among the light hole (LH), heavy hole (HH) and crystal-field split-off (SH) states. Here, optical and structural integrities of dislocation-free ultrathin GaN quantum disk (QDisk) (~ 1.2 nm) embedded in AlN barrier (~ 3 nm) grown employing plasma-assisted molecular beam epitaxy (PAMBE) are investigated considering it as a novel nanostructure to realize highly efficient TE polarized deep UV emitters. The structural and chemical integrities of thus grown QDisks are investigated by high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). We, particularly, emphasize the polarization dependent photoluminescence (PL) study of the GaN Disks to accomplish almost purely TE polarized UV (~ 260 nm) light. In addition, we observed significantly high internal quantum efficiency (IQE) of ~ 80 %, which is attributed to the enhanced overlap of the electron-hole wavefunction in extremely quantum confined ultrathin GaN QDisks, thereby presenting GaN QDisks embedded in AlN nanowires as a practical pathway towards the efficient deep UV emitters.
... The SL heterostructures consist of 50 GaN/AlN pairs. The thicknesses of each GaN and AlN layer is varied between 4 nm and 16 nm over the sample series, covering typical thicknesses for GaN/AlN quantum wells 44 and the number of layers needed for high-reflectivity bands of distributed Bragg mirrors 45,46 . A sketch of the SL structure is given in the inset to FIG. 1 (a) and in the following the SLs are indicated by SL4, SL8, SL12, SL16, where the numbers refer to the thickness of the single layers in nm. ...
Heterostructures consisting of alternating GaN/AlN epitaxial layers represent the building-blocks of state-of-the-art devices employed for active cooling and energy-saving lightning. Insights into the heat conduction of these structures are essential in the perspective of improving the heat management for prospective applications. Here, the cross-plane (perpendicular to the sample's surface) thermal conductivity of GaN/AlN superlattices as a function of the layers' thickness is established by employing the $3\omega$-method. Moreover, the role of interdiffusion at the interfaces on the phonon scattering is taken into account in the modelling and data treatment. It is found, that the cross-plane thermal conductivity of the epitaxial heterostructures can be driven to values as low as 5.9 W/(m$\cdot$K) comparable with those reported for amorphous films, thus opening wide perspectives for optimized heat management in III-nitride-based epitaxial multilayers.
