On-axis Si Research Articles

1.3 μm InAs/GaAs quantum-dot lasers grown on planar on-axis Si (001) substrates with high slope-efficiency and low differential resistance

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 μm 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 μm cavity length and 15 μm 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 μm wavelength under CW conditions at room temperature (25 °C). Importantly, these results provide an effective strategy to achieve 1.3 μm wavelength band single-mode distributed feedback lasers directly on planar on-axis Si (001) substrates with high efficiency.

Reduction of Structural Defects in the GaSb Buffer Layer on (001) GaP/Si for High Performance InGaSb/GaSb Quantum Well Light-Emitting Diodes.

Monolithic integration of GaSb-based optoelectronic devices on Si is a promising approach for achieving a low-cost, compact, and scalable infrared photonics platform. While tremendous efforts have been put into reducing dislocation densities by using various defect filter layers, exploring other types of extended crystal defects that can exist on GaSb/Si buffers has largely been neglected. Here, we show that GaSb growth on Si generates a high density of micro-twin (MT) defects as well as threading dislocations (TDs) to accommodate the extremely large misfit between GaSb and Si. We found that a 250 nm AlSb single insertion layer is more effective than AlSb/GaSb strained superlattices in reducing both types of defects, resulting in a 4× and 13× reduction in TD density and MT density, respectively, compared with a reference sample with no defect filter layer. InGaSb quantum well light-emitting diodes were grown on the GaSb/Si templates, and the effect of TD density and MT density on their performance was studied. This work shows the importance of using appropriate defect filter layers for high performance GaSb-based optoelectronic devices on standard on-axis (001) Si via direct epitaxial growth.

Reliability enhancement of InGaAs/AlGaAs quantum-well lasers on on-axis Si (001) substrate

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.

Selective area growth of high quality GaN nanocolumns on Si(0 0 1) by plasma assisted molecular beam epitaxy

Two different arrays of GaN nanocolumns, with average diameters of 140 nm and 260 nm, were selectively grown by molecular beam epitaxy on GaN-buffered on-axis Si(001) substrates. Footprint of the nanocolumns with respect to the grain size of the GaN buffer layer plays and important role on the crystalline quality of the nanocolumnar material. Despite the rather low crystalline quality of the GaN buffer, very high quality GaN nanocolumns were achieved in the case of the array with 140 nm average diameter, as indicated from a low temperature photoluminescence donor-bound exciton linewidth of 1.9 meV and negligible densities of stacking faults and threading dislocations determined by transmission electron microscopy. These results may help to the integration of GaN-based nano-devices with the conventional Si(001) electronics platform.

Ultra-high thermal stability InAs/GaAs quantum dot lasers grown on on-axis Si (001) with a record-high continuous-wave operating temperature of 150 °C.

Direct epitaxial growth of group III-V light sources with excellently thermal performance on silicon photonics chips promises low-cost, low-power-consumption, high-performance photonic integrated circuits. Here, we report on the achievement of ultra-high thermal stability 1.3 µm InAs/GaAs quantum dot (QD) lasers directly grown on an on-axis Si (001) with a record-high continuous-wave (CW) operating temperature of 150 °C. A GaAs buffer layer with a low threading dislocation density (TDD) of 4.3 × 106 cm-2 was first deposited using an optimized three-step growth method by molecular beam epitaxy. Then, an eight-layer QD laser structure with p-type modulation doping to enhance the temperature stability of the device was subsequently grown on the low TDD Si-based GaAs buffer layer. It is shown that the QD laser exhibits the ultra-high temperature stability with a characteristic temperature T0=∞ and T1=∞ in the wide temperature range of 10-75 °C and 10-140 °C, respectively. Moreover, a maximum CW operating temperature of up to 150 °C and a pulsed operating temperature of up to 160 °C are achieved for the QD laser. In addition, the QD laser shows a high CW saturation power of 50 mW at 85 °C and 19 mW at 125 °C, respectively.

Epitaxial GaSb films directly grown on on-axis Si(001) with low defect density by MBE

In recent years, GaSb-on-Si direct heteroepitaxy has been highly desirable to extend the operating wavelength range into mid-infrared and high-mobility applications, such as free-space communications, gas sensing, and hyperspectral imaging. High-quality GaSb films on Si remain challenging due to the high density of defects generated during the growth. For this purpose, epitaxial GaSb films were grown by molecular beam epitaxy on on-axis Si(001). Due to the large lattice mismatch (12.2%) between GaSb and Si, here, we proposed a radical design and growth strategy with the primary objective of achieving the annihilation of antiphase boundaries (APBs) and the reduction of threading dislocation density (TDD). Benefitting from a V-grooved Si hollow structure, we demonstrated the growth of emerging-APB-free GaSb film on Si(001) with low mosaicity. Moreover, by introducing InGaSb/GaSb dislocation filtering layers, the atomically flat surface root mean square roughness is improved to 0.34 (on Si) and 0.14 nm (on GaAs/Si). Moreover, the corresponding TDD can be reduced to 3.5 × 107 and 2 × 107 cm−2, respectively, one order of magnitude lower than the minimum value found in the literature. These reported results are a powerful lever to improve the overall quality of epitaxial Si-based antimonide, which is of high interest for various devices and critical applications, such as laser diodes, photo-detectors, and solar cells.

InAs/GaAs quantum-dot lasers grown on on-axis Si (001) without dislocation filter layers.

InAs/GaAs quantum dot (QD) laser monolithically grown on silicon is one of the potential approaches to realizing silicon-based light sources. However, the mismatch between GaAs and Si generates a high density of threading dislocations (TDs) and antiphase boundaries (APBs), which trap carriers and adversely affect device performance. In this paper, we present a simple method to reduce the threading dislocation density (TDD) merely through GaAs buffer, eliminating the intricate dislocation filter layers (DFLs) as well as any intermediate buffer layers whose compositions are different from the target GaAs. An APB-free epitaxial 2.5 µm GaAs film was grown on exact Si (001) by metalorganic chemical vapor deposition (MOCVD) with a TDD of 9.4 × 106 cm-2. InAs/GaAs QDs with a density of 5.2 × 1010 cm-2 were grown on this GaAs/Si (001) virtual substrate by molecular beam epitaxy (MBE) system. The fabricated QD laser has achieved a single facet room temperature continuous-wave output power of 138 mW with a threshold current density of 397 A/cm2 and a lasing wavelength of 1306 nm. In this work, we propose a simplified method to fabricate high-power QD lasers, which is expected to promote the application of photonic integrated circuits.

High-quality GaSb epitaxially grown on Si (001) through defects self-annihilation for CMOS-compatible near-IR light emitters

Direct epitaxial growth of III-V materials on complementary metal-oxide-semiconductor (CMOS)-compatible Si substrates has long been a scientific and engineering problem for next-generation light-emitters and non-volatile memories etc. The challenges arise from the lattice mismatch, thermal mismatch, and polarity mismatch between these materials. We report a detailed study of growing high-quality GaSb epilayers with low defect density on on-axis silicon substrates by interface engineering through all-molecular beam epitaxy (MBE) technology. We also systematically investigated the defect self-annihilation mechanism of GaSb epitaxially grown on on-axis Si (001) substrates. It was found that the misfit dislocation array was formed at the interface of AlSb/Si; threading dislocations and antiphase domain boundary annihilated at the initial GaSb layer promoted by the high-density AlSb islands, which was confirmed by transmission electron microscopy (TEM) results. Finally, a 2 µm GaSb epilayer with a step-flow surface, root-mean-square (RMS) roughness of 0.69 nm, and a rocking curve full width at half maximum (FWHM) of 251 arcsec was obtained. The photoluminescence in the near-infrared region of the GaSb/AlGaSb quantum well grown on Si substrate was also demonstrated. Our results highlighted the possible step towards the all-MBE direct growth of Sb-based infrared optoelectronic and microelectronic devices on CMOS-compatible Si substrates.

Single-Mode Photonic Crystal Nanobeam Lasers Monolithically Grown on Si for Dense Integration

Ultra-compact III-V nanolasers monolithically integrated on Si with ultra-low energy consumption and small modal volume have been emerged as one of the most promising candidates to achieve Si on-chip light sources. However, the significant material dissimilarities between III-V and Si fundamentally limit the performance of Si-based III-V nanolasers. In this work, we report 1.3 μm InAs/GaAs quantum-dot photonic-crystal (PhC) nanobeam lasers directly grown on complementary metal-oxide-semiconductor compatible on-axis Si (001) substrates. The continuous-wave optically pumped PhC nanobeam lasers exhibited a single-mode operation, with an ultra-low lasing threshold of ∼ 0.8 μW at room temperature. In addition, a nanoscale physical volume of ∼ 8 × 0.53 × 0.36 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> (∼ 25 (λ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) was realized through a small number of air-holes in PhC nanobeam laser. The promising characteristics of the PhC nanobeam lasers with small footprint and ultra-low energy consumption show their advanced potential towards densely integrated Si photonic integrated circuits.

Low threading dislocation density and antiphase boundary free GaAs epitaxially grown on on-axis Si (001) substrates.

Epitaxial growth of III-V materials on a CMOS-compatible Si (001) substrate enables the feasibility of mass production of low-cost and high-yield Si-based III-V optoelectronic devices. However, the material dissimilarities between III-V and group-IV materials induce several types of defects, especially threading dislocations (TDs) and antiphase boundaries (APBs). The presence of these defects is detrimental to the optoelectronic device performance and thus needs to be eliminated. In this paper, the mechanism of APB annihilation during the growth of GaAs on on-axis Si (001) is clarified, along with a detailed investigation of the interaction between TDs and the periodic {110} APBs. A significant reduction in the TD density ascribed to the presence of periodic APBs is discussed. This new observation opens the possibility of reducing both APBs and TDs simultaneously by utilising optimised GaAs growth methods in the future. Hence, a thin APB-free GaAs/Si (001) platform with a low TD density (TDD) was obtained. Based on this platform, a high-performance high-yield III-V optoelectronic device grown on CMOS-compatible Si (001) substrates with an overall thickness below the cracking threshold is feasible, enabling the mass production of Si-based photonic integrated circuits (PICs).

Theoretical and experimental study on epitaxial growth of antiphase boundary free GaAs on hydrogenated on-axis Si(001) surfaces

The formation of double-layer atomic steps on Si(001) surfaces is an efficient way to eliminate the antiphase boundaries (APBs) on GaAs/Si(001) interfaces. The surface energy of on-axis Si(001) surfaces with different atomic step structures was calculated and analyzed from the first principles. An optimal hydrogen-annealing process condition, the hydrogen pressure of 800 mbar and the annealing temperature of 800 °C for 10 min, was obtained experimentally. Under this annealing condition, a 420 nm APB-free GaAs epitaxial layer grown on on-axis Si(001) substrates was achieved by metal-organic chemical vapor deposition. The effect of the annealing temperature on the APB density of the GaAs/Si(001) samples was explained from the aspects of thermodynamics and kinetics. It is of great significance to optimize the growth conditions of APB-free III–V epitaxial materials on on-axis Si(001) surfaces for the large-scale silicon monolithic integration of optoelectronic devices.

C and L band room-temperature continuous-wave InP-based microdisk lasers grown on silicon.

Quantum-dot (QD) and quantum-dash (QDash) have been shown to be promising gain materials for lasers directly grown on Si due to their better tolerance to crystal defects and thermal stability. Here we report optically pumped InP-based InAs QDash microdisk lasers (MDLs) directly grown on on-axis (001) Si. To the best of our knowledge, this is the first demonstration of room-temperature continuous-wave lasing of a QDash MDL on Si in the C band and L band. To the best of our knowledge, the lowest threshold of around 400 µW and highest operation temperature of 323 K have been achieved. An analysis of experimental results shows that the dominant lasing wavelength of MDLs varies with the thickness and diameter of the MDLs. Our demonstration shows potential application of MDLs for multi-channel operation in densely integrated Si-photonics.

High-temperature reliable quantum-dot lasers on Si with misfit and threading dislocation filters

Direct epitaxial growth of III-V light sources on Si photonic chips is promising to realize low-cost and high-functionality photonic integrated circuits. Historically, high temperature reliability of such devices has been the major roadblock due to crystalline defects from heteroepitaxy. Here, by reducing the threading dislocation densities to ∼ 1 × 1 0 6 c m − 2 and efficiently removing misfit dislocations above and below the active region, 1.3 µm InAs quantum-dot lasers directly grown on industry standard on-axis Si (001) show record-breaking reliability at 80°C. The hero device shows minimum degradation after more than 1200 h of constant current stress. Statistical analysis shows an extrapolated lifetime of over 22 years for the median devices, bringing these devices one big step closer to real world applications.

Temperature-dependent photoluminescence of InAs quantum dots Grown on Silicon

This paper presents detailed studies on the temperature dependent photoluminescence (PL) of self-assembled InAs/GaAs quantum dots grown on planar on-axis Si (001) substrates. Through the analyze, we have a better understanding of carrier transport processes into InAs/GaAs quantum dots system. Before 160K, the carrier transport from wetting layer to excited states (ES) and ground states (GS) is domination. As the temperature keeps rising, carrier thermal escape from GS to ES is domination.

GaSb-based laser diodes grown on MOCVD GaAs-on-Si templates.

We report GaSb-based laser diodes (LDs) grown on on-axis (001) Si substrates and emitting at 2.3 µm. Two series of LDs were studied and compared. For the first series, a GaAs-based buffer layer was first grown by metal organic chemical vapor deposition (MOCVD) before growing the laser heterostructure by molecular-beam epitaxy (MBE). For the second series, a MOCVD GaSb buffer layer was added between the MOCVD GaAs buffer layer and the MBE laser heterostructure. Both series of LDs exhibited threshold currents in the 50-100 mA range and several mW output power at room temperature. They demonstrated continuous wave operation (CW) up to 70°C (set-up limited) without thermal rollover. Broad area LDs exhibited record threshold-current densities in the 250-350 A.cm-2 range for the second series of LDs, in spite of cracks that appeared during device processing. These results show that the design and fabrication steps of the buffer-layer stacks are critical issues in the epitaxial integration of GaSb-based optoelectronic devices on Si substrates and offer room for much performance improvement.

GaAs epitaxial growth on modified on-axis Si(001) substrates

In this work, the effect of the dose of implantation of Ga atoms into the silicon surface on the epitaxial growth of GaAs was investigated. We demonstrate that the deposition of GaAs occurs mainly on modified areas. Separate crystallites of GaAs with an irregular shape are formed on modified areas at the lowest dose of Ga implantation equal to 1 pC/μm2, whereas an increase in the dose of Ga implantation leads to the coalescence of GaAs areas. At a maximum dose of 21 pC/μm2, degradation of the morphology and a decrease in the degree of filling of the area are observed, which is also confirmed by an increase in the roughness of the structure.

Etched-cavity GaSb laser diodes on a MOVPE GaSb-on-Si template.

We report on 2.3-µm etched-cavity GaSb-based laser diodes (LDs) epitaxially integrated on on-axis (001)Si and benchmarked against their cleaved facet counterparts. The LDs were grown in two steps. First, a GaSb-on-Si template was grown by metal-organic vapor phase epitaxy (MOVPE) before the growth of the LD heterostructure by molecular-beam epitaxy. Different etched-facet geometries operate in continuous wave well above room temperature, and their performance are similar to those of cleaved-cavity LDs. These results show that etching mirrors is a viable route to form laser cavities in the GaSb technology and that MOVPE GaSb-on-Si templates are a suitable platform for optoelectronic devices overgrowth.

1.55 µm electrically pumped continuous wave lasing of quantum dash lasers grown on silicon

Realization of fully integrated silicon photonics has been handicapped by the lack of a reliable and efficient III-V light source on Si. Specifically, electrically pumped continuous wave (CW) lasing and operation sustainable at high temperatures are critical for practical applications. Here, we present the first electrically pumped room temperature (RT) CW lasing results of 1.55 μm quantum dash (QDash) lasers directly grown on patterned on-axis (001) Si using metal organic chemical vapor deposition (MOCVD). Adopting a dash-in-well structure as the active medium, the growth of QDash was optimized on an InP on Si template. Incorporating the advantages of the optimized material growth and device fabrication, good laser performance including a low threshold current of 50 mA, a threshold current density of 1.3 kA/cm2 and operation at elevated temperature up to 59 °C in CW mode was achieved. Comparison of lasers grown on Si and native InP substrates in the same growth run was made. Based on the laser characteristics measured at room temperature and elevated temperatures, the QDash quality on the two substrates is comparable. These results suggest that MOCVD is a viable technique for lasers on Si growth and represent an advance towards silicon-based photonic-electronic integration and manufacturing.

InAs-based quantum cascade lasers grown on on-axis (001) silicon substrate

We present InAs/AlSb quantum cascade lasers (QCLs) monolithically integrated on an on-axis (001) Si substrate. The lasers emit near 8 μm with threshold current densities of 0.92–0.95 kA/cm2 at 300 K for 3.6-mm-long devices and operate in pulsed mode up to 410 K. QCLs of the same design grown for comparison on a native InAs substrate demonstrated a threshold current density of 0.75 kA/cm2 and the same maximum operating temperature. The low threshold current density of the QCLs grown on Si makes them suitable for photonic integrated sensor implementation.

Mid-infrared laser diodes epitaxially grown on on-axis (001) silicon

The direct epitaxial growth of III-V semiconductor lasers on standard, CMOS-compatible, on-axis (001) Si substrates is actively sought for the realization of active photonic integrated circuits. Here we report on the first mid-infrared semiconductor laser epitaxially grown on on-axis Si substrates, i.e., compatible with industry standards. Furthermore, these GaSb-based laser diodes demonstrate low threshold current density, low optical losses, high temperature operation, and high characteristic temperatures. These results represent a breakthrough toward the integration of semiconductor laser sources on Si for smart sensors.