GaSb-based type-I quantum well cascade diode lasers emitting at nearly 2-μm wavelength with digitally grown AlGaAsSb gradient layers

We report a GaSb-based type-I quantum well cascade diode laser emitting at nearly 2-μm wavelength. The recycling of carriers is realized by the gradient AlGaAsSb barrier and chirped GaSb/AlSb/InAs electron injector. The growth of quaternary digital alloy with a gradually changed composition by short-period superlattices is introduced in detail in this paper. And the quantum well cascade laser with 100-μm-wide, 2-mm-long ridge generates an about continuous-wave output of 0.8 W at room temperature. The characteristic temperature T₀ is estimated at above 60 K.     

Molecular Beam Epitaxy of GaSb on GaAs Substrates with AlSb Buffer Layers

We investigate the molecular beam epitaxy growth of GaSb films on GaAs substrates using AlSb buffer layers. Optimization of AlSb growth parameter is aimed at obtaining high GaSh crystal quality and smooth GaSh surface. The optimized growth temperature and thickness of AlSb layers are found to be 450℃ and 2.1 nm, respectively. A rms surface roughness of 0.67 nm over 10 × 10 μm^2 is achieved as a 0.5 μm GaSh film is grown under optimized conditions.     

Interfaces in InAs/GaSb Superlattices Grown by Molecular Beam Epitaxy

Short period InAs（4ML）/GaSb（SML） superlattices （SLs） with InSb- and mixed-like （or Ga1-xInxAs1-ySby- like） interfaces （IFs） are grown by molecular-beam epitaxy （MBE） on （001） GaSh substrates at optimized growth temperature. Raman scattering reveals that two kinds of IFs can be formed by controlling shutter sequences. X-ray diffraction （XRD） and atomic force microscopy （AFM） demonstrate that SLs with mixed-like IFs are more sensitive to growth temperature than that with InSb-like IFs. The photoluminescence （PL） spectra of SLs with mixed-like IFs show a stronger intensity and narrower line width than with InSb-like IFs. It is concluded that InAs/GaSb SLs with mixed-like IFs have better crystalline and optical properties.     

An effective reflectance method for designing broadband antireflection films coupled with solar cells

The solar spectrum covers a broad wavelength range, which requires that antireflection coating (ARC) is effective over a relatively wide wavelength range for more incident light coming into the cell. In this paper, we present two methods to measure the composite reflection of SiO₂/ZnS double-layer ARC in the wavelength ranges of 300-870 nm (dual-junction) and 300-1850 nm (triple-junction), under the solar spectrum AM0. In order to give sufficient consideration to the ARC coupled with the window layer and the dispersion effect of the refractive index of each layer, we use multi-dimensional matrix data for reliable simulation. A comparison between the results obtained from the weighted-average reflectance (WAR) method commonly used and that from the effective-average reflectance (EAR) method introduced here shows that the optimized ARC through minimizing the effective-average reflectance is convenient and available.     

Growth of high material quality InAs/GaSb type-II superlattice for long-wavelength infrared range by molecular beam epitaxy

By optimizing the V/III beam-equivalent pressure ratio, a high-quality InAs/GaSb type-II superlattice material for the long-wavelength infrared (LWIR) range is achieved by molecular beam epitaxy (MBE). High-resolution x-ray diffraction (HRXRD), atomic force microscopy (AFM), and Fourier transform infrared (FTIR) spectrometer are used to characterize the material growth quality. The results show that the full width at half maximum (FWHM) of the superlattice zero-order diffraction peak, the mismatching of the superlattice zero-order diffraction peak between the substrate diffraction peaks, and the surface roughness get the best results when the beam-equivalent pressure (BEP) ratio reaches the optimal value, which are 28 arcsec, 13 arcsec, and 1.63 Å, respectively. The intensity of the zero-order diffraction peak is strongest at the optimal value. The relative spectral response of the LWIR detector shows that it exhibits a 100% cut-off wavelength of 12.6 μm at 77 K. High-quality epitaxial materials have laid a good foundation for preparing high-performance LWIR detector.     

InGaAs/GaAs应变脊形量子线分子束外延非平面生长研究

提出了新型InGaAs/GaAs应变脊形量子线结构．这种应变脊形量子线结合了非平面应变外延层中沿不同晶向能带带隙的变化、非平面生长应变层In组分的变化，以及非平面外延层厚度的变化等三方面共同形成的横向量子限制效应的综合作用．在非平面GaAs衬底上用分子束外延生长了侧面取向为（113）的脊形AlAs/In GaAs/AlAs应变量子线．用10K光致荧光谱测试了其发光性质．用Kronig-Penney模型近似计算了这种应变脊形结构所具有的横向量子限制效应，发现其光致荧光谱峰位的测试结果，与计算结果相比，有10meV的“蓝移”．认为这一跃迁能量的“蓝移”是上述三方面横向量子限制效应综合作用的结果 关键词：     

垂直耦合自组织InAs双量子点中激子能的计算

在有效质量近似条件下研究了垂直耦合的自组织InAs/GaAs量子点的激子态.在绝热近似条件下，采用传递矩阵方法计算了电子和空穴的能谱.通过哈密顿量矩阵的对角化，对电子和空穴间的库仑相互作用进行了精确处理.讨论了两量子点间的垂直距离对激子基态能的影响.从基态波函数概率分布的角度，讨论了激子的束缚能.计算了重空穴和轻空穴激子的基态能随外部垂直磁场变化的函数关系.计算了量子点大小（量子点半径）对激子能的影响. 关键词： 量子点 激子 对角化     

Room-Temperature Operation of 2.4 μm InGaAsSb/A1GaAsSb Quantum-Well Laser Diodes with Low-Threshold Current Density

GaSb-based 2.4μm InGaAsSb/AIGaAsSb type-I quantum-well laser diode is fabricated. The laser is designed consisting of three In0.35 Ga0.65As0.1Sb0.9/Al0.35 Ga0.65 As0.02Sb0.98 quantum wells with 1% compressive strain located in the central part of an undoped Al0.35Ga0.65As0.02Sb0.98 waveguide layer. The output power of the laser with a 50-μm-wide i-ram-long cavity is 28roW, and the threshold current density is 400A/cm2 under continuous wave operation mode at room temperature.     

Resonant cavity-enhanced quantum dot field-effect transistor as a single-photon detector

A resonant cavity-enhanced （RCE） quantum dot （QD） field-effect transistor （RCEQDFET） is designed for single- photon detection in this paper. Adding distributed Bragg reflection （DBR） mirrors to the single-photon detector （SPD）, we improve the light absorption efficiency of the SPD. The effects of the reflectivity of the mirrors, the thickness and light absorption coefficient of the absorbing layer on the detector＇s light absorption efficiency are investigated, and the resonant cavity is determined by using the air/semiconductor interface as the mirror on the top. Through analyzing the relationship between the refractive index of AlxGal_xAs and A1 component, we choose A1As/Alo.15Gao.85As as the material of the mirror on the bottom. The pairs of A1As/Alo.15Gao.85As film are further determined to be 21 by calculating the reflectivity of the mirror. The detector is fabricated from semiconductor heterostructures grown by molecular beam epitaxy. The reflection spectrum, photoluminescence （PL） spectrum, photocurrent response, and channel current of the detector are tested and the results show that the RCEQDFET-SPD designed in this paper has better performances in photonic response and wavelength selection.