다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Hybrid silicon lasers based on bonded III–V layers on silicon are currently the best contenders for on-chip lasers for silicon photonics. On-chip silicon light sources are highly desired for use as electrical-to-optical converters in silicon-based photonics. Zhiping Zhou and Bing Yin of Peking University in China and Jurgen Michel of Massachusetts Institute of Technology assess the three main contenders for such light sources: erbium-based light sources, germanium-on-silicon lasers and III-V-based silicon lasers. They consider operating wavelength, pumping conditions, power consumption, thermal stability and fabrication process. The scientists regard the power efficiencies of electrically pumped erbium-based lasers as being too low and the threshold currents of germanium lasers as being too high. They conclude that III–V quantum dot lasers monolithically grown on silicon show the most promise for realizing on-chip lasers.

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On-chip light sources for silicon photonics

Compound semiconductor materials such as gallium arsenide and indium arsenide have outstanding electronic properties, but are costly to process and cannot, on their own, compete with silicon when it comes to low-cost fabrication. But as the relentless miniaturization of silicon electronics is reaching its limits, an alternative route of enhanced device performance is becoming more attractive: the integration of compound semiconductors within silicon. Ali Javey and colleagues now present a promising new concept to integrate ultrathin layers of single-crystal indium arsenide on silicon-based substrates with an epitaxial transfer method, a technique borrowed from large-area optoelectronics. With this technique, involving the use of an elastomeric stamp to lift off indium arsenide nanowires and transfer them to a silicon-based substrate, the authors fabricate thin film transistors with excellent device performance. A potential route to enhancing the performance of electronic devices is to integrate compound semiconductors, which have superior electronic properties, within silicon, which is cheap to process. These authors present a promising new concept to integrate ultrathin layers of single-crystal indium arsenide on silicon-based substrates with an epitaxial transfer method borrowed from large-area optoelectronics. With this technique, the authors fabricate thin-film transistors with excellent device performance. Over the past several years, the inherent scaling limitations of silicon (Si) electron devices have fuelled the exploration of alternative semiconductors, with high carrier mobility, to further enhance device performance1,2,3,4,5,6,7,8. In particular, compound semiconductors heterogeneously integrated on Si substrates have been actively studied7,9,10: such devices combine the high mobility of III–V semiconductors and the well established, low-cost processing of Si technology. This integration, however, presents significant challenges. Conventionally, heteroepitaxial growth of complex multilayers on Si has been explored9,11,12,13—but besides complexity, high defect densities and junction leakage currents present limitations in this approach. Motivated by this challenge, here we use an epitaxial transfer method for the integration of ultrathin layers of single-crystal InAs on Si/SiO2 substrates. As a parallel with silicon-on-insulator (SOI) technology14, we use ‘XOI’ to represent our compound semiconductor-on-insulator platform. Through experiments and simulation, the electrical properties of InAs XOI transistors are explored, elucidating the critical role of quantum confinement in the transport properties of ultrathin XOI layers. Importantly, a high-quality InAs/dielectric interface is obtained by the use of a novel thermally grown interfacial InAsO x layer (~1 nm thick). The fabricated field-effect transistors exhibit a peak transconductance of ~1.6 mS µm−1 at a drain–source voltage of 0.5 V, with an on/off current ratio of greater than 10,000.

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Ultrathin compound semiconductor on insulator layers for high-performance nanoscale transistors

GaP tensile strain compensation (SC) layers were introduced into GaAs solar cells enhanced with a five layer stack of InAs quantum dots (QDs). One sun air mass zero illuminated current-voltage curves show that SC results in improved conversion efficiency and reduced dark current. The strain compensated QD solar cell shows a slight increase in short circuit current compared to a baseline GaAs cell due to sub-GaAs bandgap absorption by the InAs QD. Quantum efficiency and electroluminescence were also measured and provide further insight to the improvements due to SC.

Effect of strain compensation on quantum dot enhanced GaAs solar cells

The efficiency in modern technologies and green energy solutions has boiled down to a thermal engineering problem on the nanoscale. Due to the magnitudes of the thermal mean free paths approaching or overpassing typical length scales in nanomaterials (i.e., materials with length scales less than one micrometer), the thermal transport across interfaces can dictate the overall thermal resistance in nanosystems. However, the fundamental mechanisms driving these electron and phonon interactions at nanoscale interfaces are difficult to predict and control since the thermal boundary conductance across interfaces is intimately related to the characteristics of the interface (structure, bonding, geometry, etc.) in addition to the fundamental atomistic properties of the materials comprising the interface itself. In this paper, I review the recent experimental progress in understanding the interplay between interfacial properties on the atomic scale and thermal transport across solid interfaces. I focus this discussion specifically on the role of interfacial nanoscale “imperfections,” such as surface roughness, compositional disorder, atomic dislocations, or interfacial bonding. Each type of interfacial imperfection leads to different scattering mechanisms that can be used to control the thermal boundary conductance. This offers a unique avenue for controlling scattering and thermal transport in nanotechnology.

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Thermal Transport across Solid Interfaces with Nanoscale Imperfections: Effects of Roughness, Disorder, Dislocations, and Bonding on Thermal Boundary Conductance

We demonstrate the growth of a low dislocation density, relaxed GaSb bulk layer on a (001) GaAs substrate. The strain energy generated by the 7.78% lattice mismatch is relieved by a periodic array of 90° misfit dislocations. The misfit array is localized at the GaSb∕GaAs interface and has a period of 5.6nm which is determined by transmission electron microscope images. No threading dislocations are visible. The misfits are identified as 90°, rather than 60°, using Burger’s circuit analysis, and are therefore not associated with generation of threading dislocations. A low dislocation density and planar growth mode is established after only 3 monolayers of GaSb deposition as revealed by reflection high-energy electron diffraction patterns. Calculations corroborate the materials characterization and indicate the strain energy generated by the 7.78% lattice mismatch is almost fully dissipated by the misfit array. The low dislocation density bulk GaSb material on GaAs enabled by this growth mode will lead to new devices, especially in the infrared regime, along with novel integration schemes.

Strain relief by periodic misfit arrays for low defect density GaSb on GaAs

The authors report an enhanced infrared spectral response of GaAs-based solar cells that incorporate type II GaSb quantum dots (QDs) formed using interfacial misfit array growth mode. The material and devices, grown by molecular beam epitaxy, are characterized by current-voltage and spectral response characteristics. From 0.9to1.36μm, these solar cells show significantly more infrared response compared to reference GaAs cells and previously reported InAs QD solar cells. The short circuit current density and open circuit voltages of solar cells with and without dots measured under identical conditions are 1.29mA∕cm2, 0.37V and 1.17mA∕cm2, 0.6V, respectively.

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GaSb∕GaAs type II quantum dot solar cells for enhanced infrared spectral response

Publisher Summary This chapter provides an overview of type-II superlattice infrared detectors. The type-II InAs/GaSb superlattices have several fundamental properties that make them suitable for infrared detection: (1) their band gaps can be made arbitrarily small by design, (2) they are more immune to band-to-band tunneling compared with bulk material, (3) the judicious use of strain in type-II InAs/GaInSb strained layer superlattice (SLS) can enhance its absorption strength over that of the type-II InAs/GaSb superlattice to a level comparable with HgVdTe (MCT), and (4) type-II InAs/Ga(In)Sb superlattices also reduce Auger recombination. In addition, the dark current characteristics of type-II superlattice-based single element long-wavelength infrared (LWIR) detectors are currently approaching state-of-the-art MCT detector. Noise measurements highlight the need for surface leakage suppression, which can be tackled by improved etching, passivation, and device design. The chapter also describes the principles behind advanced superlattice infrared detectors based on heterostructure designs. It also explores some aspects of device fabrication and characterization.

Type-II Superlattice Infrared Detectors

We report on the multispectral properties of infrared photodetectors based on type II InAs∕Ga(In)Sb strain layer superlattices using an nBn heterostructure design. The optical and electrical properties of the midwave and long wave infrared (MWIR-LWIR) absorbing layers are characterized using spectral response and current-voltage measurements, respectively. The dual band response is achieved by changing the polarity of applied bias. The spectral response shows a significant change in the LWIR to MWIR ratio within a very small bias range (∼100mV), making it compatible with commercially available readout integrated circuits.

Bias dependent dual band response from InAs∕Ga(In)Sb type II strain layer superlattice detectors

The authors demonstrate and characterize type-II GaSb quantum dot (QD) formation on GaAs by either Stranski-Krastanov (SK) or interfacial misfit (IMF) growth mode. The growth mode selection is controlled by the gallium to antimony (III/V) ratio where a high III/V ratio produces IMF and a low ratio establishes the SK growth mode. The IMF growth mode produces strain-relaxed QDs, where the SK QDs remain highly strained. Both ensembles demonstrate strong room temperature photoluminescence (PL) with the SK QDs emitting at 1180nm and the IMF QDs emitting at 1375nm. Quantized energy levels along with a spectral blueshift are observed in 77K PL. Transmission electron microscope images identify the IMF array and crystallographic shape for both types of QD formation. Atomic force microscope images characterize QD geometry and density.

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Arezou Khoshakhlagh

Papers

Strain relief by periodic misfit arrays for low defect density GaSb on GaAs

GaSb∕GaAs type II quantum dot solar cells for enhanced infrared spectral response

Type-II Superlattice Infrared Detectors

Bias dependent dual band response from InAs∕Ga(In)Sb type II strain layer superlattice detectors

III/V ratio based selectivity between strained Stranski-Krastanov and strain-free GaSb quantum dots on GaAs