Qiang Li

Growing antiphase-domain-free GaAs thin films out of highly ordered planar nanowire arrays on exact (001) silicon

We report the use of highly ordered, dense, and regular arrays of in-plane GaAs nanowires as building blocks to produce antiphase-domain-free GaAs thin films on exact (001) silicon. High quality GaAs nanowires were grown on V-grooved Si (001) substrates using the selective aspect ratio trapping concept. The 4.1% lattice mismatch has been accommodated by the initial GaAs, a few nanometer-thick with high density stacking faults. The bulk of the GaAs wires exhibited smooth facets and a low defect density. An unusual defect trapping mechanism by a “tiara”-like structure formed by Si undercuts was discovered. As a result, we were able to grow large-area antiphase-domain-free GaAs thin films out of the nanowires without using SiO2 sidewalls for defect termination. Analysis from XRD ω-rocking curves yielded full-width-at-half-maximum values of 238 and 154u2009arc sec from 900 to 2000u2009nm GaAs thin films, respectively, indicating high crystalline quality. The growth scheme in this work offers a promising path towards ...

Optically pumped 1.3 μm room-temperature InAs quantum-dot micro-disk lasers directly grown on (001) silicon

Direct integration of high-performance laser diodes on silicon will dramatically transform the world of photonics, expediting the progress toward low-cost and compact photonic integrated circuits (PICs) on the mainstream silicon platform. Here, we report, to the best of our knowledge, the first 1.3 μm room-temperature continuous-wave InAs quantum-dot micro-disk lasers epitaxially grown on industrial-compatible Si (001) substrates without offcut. The lasing threshold is as low as hundreds of microwatts, similar to the thresholds of identical lasers grown on a GaAs substrate. The heteroepitaxial structure employed here does not require the use of an absorptive germanium buffer and/or dislocation filter layers, both of which impede the efficient coupling of light from the laser active regions to silicon waveguides. This allows for full compatibility with the extensive silicon-on-insulator (SOI) technology. The large-area virtual GaAs (on Si) substrates can be directly adopted in various mature in-plane laser configurations, both optically and electrically. Thus, this demonstration represents a major advancement toward the commercial success of fully integrated silicon photonics.

Sub-wavelength InAs quantum dot micro-disk lasers epitaxially grown on exact Si (001) substrates

Subwavelength micro-disk lasers (MDLs) as small as 1u2009μm in diameter on exact (001) silicon were fabricated using colloidal lithography. The micro-cavity gain medium incorporating five-stacked InAs quantum dot layers was grown on a high crystalline quality GaAs-on-V-grooved-Si template with no absorptive intermediate buffers. Under continuous-wave optical pumping, the MDLs on silicon exhibit lasing in the 1.2-μm wavelength range with low thresholds down to 35u2009μW at 10u2009K. The MDLs compare favorably with devices fabricated on native GaAs substrates and state-of-the-art work reported elsewhere. Feasibility of device miniaturization can be projected by size-dependent lasing characteristics. The results show a promising path towards dense integration of photonic components on the mainstream complementary metal–oxide–semiconductor platform.

Electrically pumped continuous wave quantum dot lasers epitaxially grown on patterned, on-axis (001) Si

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.

GaAs-InGaAs-GaAs Fin-Array Tunnel Diodes on (001) Si Substrates With Room-Temperature Peak-to-Valley Current Ratio of 5.4

In this letter, we report the selective area growth of GaAs, In_0.2Ga_0.8As, and GaAs/In_0.2Ga_0.8As/GaAs quantum-well fins of 65-nm width on exactly orientated (001) Si substrates. By exploiting high aspect ratio trenches formed by patterned SiO₂ on Si and a V-grooved Si (111) surface in the aspect ratio trapping process, we are able to achieve good material quality and structural properties, as evidenced by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The fabricated GaAs-In_0.2Ga_0.8As-GaAs fin-array tunnel diodes exhibit a maximum room-temperature peak-to-valley current ratio of 5.4, and negative differential resistance characteristics up to 200 °C.

Growth of ultra-high mobility In0.52Al0.48As/InxGa1−xAs (x ≥ 53%) quantum wells on Si substrates using InP/GaAs buffers by metalorganic chemical vapor deposition

InGaAs quantum wells (QWs) cladded by InAlAs barriers were grown on Si by metalorganic chemical vapor deposition. InP/GaAs/Si buffer templates were first prepared using a two-step growth method. We were able to significantly reduce the dislocation density in the upper InP buffer and obtain smooth surface morphology by fine-tuning the growth parameters and inserting an InGaAs interlayer in the InP buffer. On these InP/GaAs/Si compliant substrates, we investigated InGaAs QWs with various well/barrier parameters and Si-delta doping. We obtained two-dimensional electron gas mobilities over 10,000 cm2 V−1 s−1 at 300 K and above 39,000 cm2 V−1 s−1 at 77 K on Si substrates.

Growing InGaAs quasi-quantum wires inside semi-rhombic shaped planar InP nanowires on exact (001) silicon

We report InGaAs quasi-quantum wires embedded in planar InP nanowires grown on (001) silicon emitting in the 1550u2009nm communication band. An array of highly ordered InP nanowire with semi-rhombic cross-section was obtained in pre-defined silicon V-grooves through selective-area hetero-epitaxy. The 8% lattice mismatch between InP and Si was accommodated by an ultra-thin stacking disordered InP/GaAs nucleation layer. X-ray diffraction and transmission electron microscope characterizations suggest excellent crystalline quality of the nanowires. By exploiting the morphological evolution of the InP and a self-limiting growth process in the V-grooves, we grew embedded InGaAs quantum-wells and quasi-quantum-wires with tunable shape and position. Room temperature analysis reveals substantially improved photoluminescence in the quasi-quantum wires as compared to the quantum-well reference, due to the reduced intrusion defects and enhanced quantum confinement. These results show great promise for integration of III-...

1.3 μm Submilliamp Threshold Quantum Dot Micro-lasers on Si

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 1.3xa0μm communication wavelength. A submilliamp threshold of 0.6xa0mA was achieved for a micro-laser with a radius of 5xa0μm. The thresholds and footprints are orders of magnitude smaller than those previously reported lasers epitaxially grown on Si.

1.3-μm InAs quantum-dot micro-disk lasers on V-groove patterned and unpatterned (001) silicon.

We report comparison of lasing dynamics in InAs quantum dot (QD) micro-disk lasers (MDLs) monolithically grown on V-groove patterned and planar Si (001) substrates. TEM characterizations reveal abrupt interfaces and reduced threading dislocations in the QD active regions when using the GaAs-on-V-grooved-Si template. The improved crystalline quality translates into lower threshold power in the optically pumped continuous-wave MDLs. Concurrent evaluations were also made with devices fabricated simultaneously on lattice-matched GaAs substrates. Lasing behaviors from 10 K up to room temperature have been studied systematically. The analyses spotlight insights into the optimal epitaxial scheme to achieve low-threshold lasing in telecommunication wavelengths on exact Si (001) substrates.

Monolithic Integration of Tunnel Diode-Based Inverters on Exact (001) Si Substrates

Monolithic integration of tunnel diode-based inverters on exact (001) Si substrates for the future high-speed, low-power, and compact digital circuits is demonstrated. A two-state inverter was fabricated using a forward biased fin-array tunnel diode as drive and a reverse-biased counterpart as load. On-chip operation and reduced fabrication complexity were achieved by exploiting the resistive characteristic of the reverse-biased tunnel diodes and the pre-defined patterns on the Si substrate.