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(a) Schematic of the QD laser structure on exact Si (001) substrates with asymmetric waveguide structure grown by both MOCVD and MBE technologies. (b) 10µm×10µm AFM image of 420 nm GaAs buffers grown on exact Si (001) substrates with a root mean square roughness of 0.99 nm. (c) Room-temperature photoluminescence spectrum of the QD active region grown on the Si template, and the inset is 1×1 µm² AFM image of uncapped InAs QDs with the QD density of 4.6×10¹⁰ cm⁻².
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We report electrically pumped continuous-wave (CW) InAs/GaAs quantum dot lasers directly grown on planar exact silicon (001) with asymmetric waveguide structures. Surface hydrogen-annealing for the GaAs/ Si (001) templates and low-temperature growth for GaInP upper cladding layers were combined in the growth of the laser structure to achieve a high...
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... Currently, semiconductor chips have been facing great challenges in high-speed data transmission and processing with the intensification of the global digitalization process, especially in data center applications. Optical interconnect technology has attracted great interest and been extensively studied in recent years due to its advantages in high transmission rate, high stability, large capacity, small size, and low energy consumption in the field of silicon photonic chips [1]. Up to date, the monolithic integration of III-V materials on silicon platform is one of the promising methods to realize optical interconnection because such heterogeneous combination allows us to benefit from both the maturity of the Si-based chips manufacturing technology (complementary metal oxide semiconductor) and the III-V material electronic and optical properties (high electron mobility, direct band gap, etc) [2,3]. ...
Herein, we report the phase transformation mechanism of the nominal Si(001) surface driven by hydrogen thermal annealing. The surface energies of H-terminated Si(001) surface with different phase structures were calculated by density functional theory. The results show that the surface phase with monoatomic steps can transform into the surface phase with diatomic steps under proper ranges of hydrogen chemical potential. Combining thermodynamic and kinetic factors, the phase transformation can’t occur when annealing temperature lower or higher than 800 °C. In addition, surface phases with different types of diatomic steps are alternately transformed through the intermediate phase with monoatomic steps and the imperfection of the transformation process gradually increases with the extension of annealing time. Finally, different experiments have been carried and the experimental results are in good agreement with the phase transformation mechanism. This study provides complete theoretical mechanism and process parameters for controlling the phase structures of the nominal Si(001) surface through hydrogen thermal annealing.
... As another candidate for achieving III-V light sources on Si, monolithic integration via heteroepitaxy could bring about lower cost and power consumption for Si-based photonic integrated circuits (PICs) [7]. Therefore, realizing high-quality heteroepitaxy of GaAs on Si should be the primary work because GaAs has been the widely used in Si-based quantum-well (QW) lasers and selfassembled quantum-dot (QD) lasers [8][9][10][11][12]. Nevertheless, crystal defects such as antiphase domains (APDs), threading dislocations (TDs) and thermal cracks will be induced during the epitaxy process of III-V/Si [13]. ...
... To reduce the TDs forming at the GaAs/Si interface, various methods have been taken and the surface threading dislocation density (TDD) of the GaAs epilayer was successfully reduced [14]. Among these methods, InGaAs/GaAs strained-layer superlattices (SLSs) as dislocation filter layers, which drive TDs to bend towards the strained interfaces and promote the annihilation probability of TDs, have been the most common one in a molecular beam epitaxy (MBE) system [12,15,16]. In contrast, as an indium-free technique, thermal cycle annealing (TCA) takes advantage of the thermal expansion coefficient mismatch between GaAs and Si (α GaAs − α Si ≈ 3 × 10 -6 /K) to generate thermal stress for TD's glide and annihilation. ...
Heteroepitaxy of GaAs on Si enables well-functioning III–V semiconductor lasers integrated onto silicon, solving the issue of lacking purely silicon-based light sources. Since GaAs has been the key material in many III–V laser structures, the Si-based GaAs epilayer should be of high quality which requires a low surface roughness and dislocation density. Herein, we demonstrate a high-quality heteroepitaxy of 1.84 μm GaAs on Si (001) substrates by molecular beam epitaxy. By virtue of multi-time thermal cycle annealing, the surface roughness was reduced to 1.74 nm within a scan area of 10 × 10 μm2, and the measured threading dislocation density was as low as 6.87 × 106/cm2. Periodic interfacial misfit dislocation arrays were found at the GaAs/Si interface with a misfit-dislocation-spacing distance of 9.6 nm. The formation of these arrays is attributed to the usage of thermal cycle annealing which makes near-interface TDs form into in-plane misfit dislocations. The demonstrated epitaxy scheme of growing such high-quality GaAs/Si virtual substrates provides a feasible way to fabricate III–V semiconductor lasers with enhanced performances.
... As to the advancement of the monolithic on-axis Si (001)-based lasers, InAs/GaAs quantum-dot (QD) lasers have nearly reached ARTICLE pubs.aip.org/aip/apm their maturity with quite high operation stability due to their high tolerance to crystal defects, [23][24][25][26][27][28][29][30][31] while their quantum-well (QW) counterparts, which should be more favorable for the transplantation of the mature III-V optoelectronic technologies as a whole to the silicon-based ones, have just shown some initial breakthroughs. Actually, mainly by virtue of the hard efforts on the complete prevention or elimination of APDs and a quite effective TDD reduction, the room-temperature and continuous-wave (RTCW) operation of InGaAs/AlGaAs QW and (InGaAs/GaAs/GaAsP)/AlGaAs QW lasers epitaxially grown on on-axis Si (001) have been realized 32,33 with an initial CW lifetime record of ∼90 s (at 25 ○ C). 32 However, as to further enhancement of the reliability of InGaAs/AlGaAs QW lasers, one more problem in addition to the APDs and TDs has to be taken into account. ...
... Then, the wafer was transferred into the growth chamber, and a 10 min hydrogen annealing with an annealing temperature of 800 ○ C was conducted to prevent the later-on generation of APDs at the GaAs/Si interface. 16 Then carried out was a three-step growth of GaAs epilayers including a 20 nm lowtemperature layer grown at 390 ○ C, a 100 nm mid-temperature layer at 570 ○ C and a 300 nm high-temperature layer at 650 ○ C. 16,30 As shown in Fig. 1(b), the as-grown structure, we call it the GaAs/Si (001) virtual substrate, features an APD-free surface with a rootmean-square (RMS) roughness of 0.88 nm within a scan area of 10 × 10 μm 2 , measured by atomic force microscopy (AFM). ...
The enhancement of the reliability of the silicon-based III–V quantum well lasers, especially of those on an on-axis Si (001) substrate, is of great importance now a days for the development of Si-based photonic and even optoelectronic integrated circuits and is really quite challenging. As an experimental advancement, mainly by inserting a pair of InAlAs strained layers separately into the upper and lower AlGaAs cladding layers to effectively prevent the formation of the in-plane gliding misfit-dislocations within the boundary planes of the active region, the longest room-temperature and continuous-wave lifetime of the InGaAs/AlGaAs quantum well lasers on an on-axis Si (001) substrate with a cavity length of 1500 µm and a ridge width of 20 µm has been prolonged from a very initial record of ∼90 s to the present length longer than 31 min. While, the highest continuous-wave operation temperature of another one with a cavity length of 1000 µm and a ridge width of 10 µm has been shown as 103 °C with an extracted characteristic temperature of 152.7 K, further enhancement of the device reliability is still expected and would mainly depend on the level of the threading-dislocation-density reduction in the GaAs/Si virtual substrate.
... Directly epitaxial growth of III-V quantum-dot (QD) lasers on silicon (001) substrate has been extensively investigated with dramatic progress [1][2][3][4][5], which is promising to take full advantage of CMOS process to drive low-cost, low-power consumption, and high-dense silicon photonics integrated circuits (PICs) [6]. The well-known p-type modulation doping can effectively enhance the differential gain, temperature stability, and small signal modulation response of InAs/GaAs QD lasers by compensating the loss of holes during device operation [7][8][9][10]. ...
We report the significantly enhanced performance of InAs/GaAs quantum dot (QD) lasers on Si(001) by spatially separated co-doping, including n-doping in the QDs and p-doping in the barrier layers simultaneously. The QD lasers are a ridge waveguide of 6 × 1000 µm² containing five InAs QD layers. Compared with p-doped alone laser, the co-doped laser exhibits a large reduction in threshold current of 30.3% and an increase in maximum output power of 25.5% at room temperature. In the range of 15°C-115°C (under 1% pulse mode), the co-doped laser shows better temperature stability with higher characteristic temperatures of threshold current (T0) and slope efficiency (T1). Furthermore, the co-doped laser can maintain stable continuous-wave ground-state lasing up to a high temperature of 115°C. These results prove the great potential of co-doping technique for enhancing silicon-based QD laser performances towards lower power consumption, higher temperature stability, and higher operating temperature, to boost the development of high-performance silicon photonic chips.
... To date, the remarkable lasers emitting at 1.3-1.5 µm band have been successfully achieved on Si by MOCVD [12][13][14]. However, the demand for information interaction still requires a reliable 980 nm laser source for EDFAs, to achieve higher pumping efficiency and lower amplifier noise [15]. ...
Investigation of high-performance lasers monolithically grown on silicon (Si) could promote the development of silicon photonics in regimes other than the 1.3 -1.5 µm band. 980 nm laser, a widely used pumping source for erbium-doped fiber amplifier (EDFA) in the optical fiber communication system, can be used as a demonstration for shorter wavelength lasers. Here, we report continuous wave (CW) lasing of 980 nm electrically pumped quantum well (QW) lasers directly grown on Si by metalorganic chemical vapor deposition (MOCVD). Utilizing the strain compensated InGaAs/GaAs/GaAsP QW structure as the active medium, the lowest threshold current obtained from the lasers on Si was 40 mA, and the highest total output power was near 100 mW. A statistical comparison of lasers grown on native GaAs and Si substrates was conducted and it reveals a somewhat higher threshold for devices on Si. Internal parameters, including modal gain and optical loss are extracted from experimental results and the variation on different substrates could provide a direction to further laser optimization through further improvement of the GaAs/Si templates and QW design. These results demonstrate a promising step towards optoelectronic integration of QW lasers on Si.
... However, the dissimilarities between the III-V and silicon materials result in the generation of various crystal defects such as threading dislocations (TDs), film cracking, and antiphase domains (APDs)-limiting device performance and reliability [8]. In recent years, by virtue of the higher tolerance to defects, quantum dot (QD) lasers directly grown on silicon have been attracting much attention [9][10][11][12][13]. The lifetime is now more than 22 years at 85°C for the reported state-of-the-art QD lasers on silicon [14]. ...
InGaAs/AlGaAs multiple quantum well lasers grown on silicon (001) by molecular beam epitaxy have been demonstrated. By inserting InAlAs trapping layers into AlGaAs cladding layers, misfit dislocations easily located in the active region can be effectively transferred out of the active region. For comparison, the same laser structure without the InAlAs trapping layers was also grown. All these as-grown materials were fabricated into Fabry-Perot lasers with the same cavity size of 20 × 1000 µm². The laser with trapping layers achieved a 2.7-fold reduction in threshold current density under pulsed operation (5 µs-pulsed width, 1%-duty cycle) compared to the counterpart, and further realized a room-temperature continuous-wave lasing with a threshold current of 537 mA which corresponds to a threshold current density of 2.7 kA/cm². When the injection current reached 1000 mA, the single-facet maximum output power and slope efficiency were 45.3 mW and 0.143 W/A, respectively. This work demonstrates significantly improved performances of InGaAs/AlGaAs quantum well lasers monolithically grown on silicon, providing a feasible solution to optimize the InGaAs quantum well structure.
... [9][10][11][12][13] In recent years, taking the structural advantage of higher tolerance to TDs, significant advancements on silicon-based GaAs-buffered III-V quantum dots (QDs) lasers have been achieved. [14][15][16][17][18] In comparison, only some moderate advancements have been made for their quantum well (QW) counterparts although the success of the QW ones with satisfactory performance is attractive because it would make the transplant of all the currently available GaAs-based or even InPbased III-V optoelectronic technologies onto silicon platforms possible. First of all, by adopting the misoriented silicon substrates, either room-temperature (RT) continuous-wave (CW) operation or the RT pulsed operation with a threshold current density as low as 313 A/cm 2 has been realized. ...
... Subsequently, the 420 nm GaAs epilayer itself was grown, and the growth procedures have been reported in detail previously. 14,26 At the second stage of the fabrication, a prior annealing for the epilayer-surface deoxidation and the growth of the rest parts of the whole structure were conducted in a solid-source molecular beam epitaxy (MBE) system. The detailed procedures were as follows: A 300 nm GaAs buffer was grown first to flatten the surface. ...
... As the first step, to obtain a smooth epitaxial surface of the GaAs/Si (001) template, the threestep growth method was taken in MOCVD to deposit 420 nm GaAs. 14,26,29 During this process, the APDs, featuring a surface pattern of brink sags in closed loops and further deteriorating the quality of active layers seriously, were completely eliminated by the hydrogenannealing pretreatment of the silicon substrate. 26 The surface morphology of the 420 nm GaAs/Si (001) template was measured by atomic force microscopy (AFM), as shown in Fig. 2(d). ...
Room-temperature continuous-wave operation of InGaAs/AlGaAs quantum well lasers directly grown on on-axis silicon (001) has been demonstrated. A 420 nm thick GaAs epilayer completely free of antiphase domains was initially grown on the silicon substrate in a metal-organic chemical vapor deposition system and the other epilayers, including four sets of five-period strained-layer superlattices and the laser-structural layers, were successively grown in a molecular beam epitaxy system. The lasers were prepared as broad-stripe Fabry–Pérot ones with a stripe width of 21.5 μm and a cavity length of 1 mm. Typically, the threshold current and the corresponding threshold current density are 186.4 mA and 867 A/cm ² , respectively. The lasing wavelength is around 980 nm, and the slope efficiency is 0.097 W/A with a single-facet output power of 22.5 mW at an injection current of 400 mA. This advancement makes the silicon-based monolithic optoelectronic integration relevant to quantum well lasers more promising with an enhanced feasibility.
We report electrically pumped continuous-wave (CW) InAs/GaAs quantum dot lasers monolithically grown on planar on-axis Si (001) substrates. Combining an asymmetric waveguide epitaxy structure with aluminium-free upper cladding layers and a symmetrical cathode chip structure, 1.3 μ m band lasers with low differential resistance and high slope-efficiency have been achieved. Moreover, the optimized symmetrical cathode structure of the laser chips is used to improve the slope-efficiency by reducing the differential resistance and waste heat. The Fabry–Perot broad-stripe edge-emitting lasers with 2000 μ m cavity length and 15 μ m stripe width achieve a single-facet output power of 73 mW, a single-facet slope efficiency of 0.165 W A ⁻¹ , and a differential resistance of 1.31 Ω at ∼1.31 μ m wavelength under CW conditions at room temperature (25 °C). Importantly, these results provide an effective strategy to achieve 1.3 μ m wavelength band single-mode distributed feedback lasers directly on planar on-axis Si (001) substrates with high efficiency.
This paper proposes an optimization method combining the time-domain traveling wave model and the mode refractive index method, employed for characterizing both the transverse and longitudinal modes of quantum dot distributed feedback (DFB) lasers grown on Si. We use this method to optimize the overall performance of the Si-based DFB laser, and determine the material and chip structural parameters, including the ridge width, etching depth, grating thickness and grating position as optimization parameters. Here, the optimal DFB laser operating under fundamental transverse and single longitudinal mode is obtained. Its threshold current is as low as 5 mA, the slope efficiency is as high as 0.77 mW mA ⁻¹ , and the side mode suppression ratio is up to 48 dB. When the injection current is 150 mA, the output power exceeds 100 mW. The corresponding ridge width, etching depth and grating thickness are 2 μ m, 1.3 μ m and 20 nm, respectively. The distance from the grating to the active region is 200 nm. Therefore, the novel method presented in this paper offers an effective scheme for the design of DFB lasers grown on Si with excellent performance.
