Raman scattering of polycrystalline GaSb thin films grownby co-evapouration process

<正>This paper reports that GaSb thin films have been co-deposited on soda-lime glass substrates.The GaSb thin film structural properties are characterized by Raman spectroscopy.The Sb-A_1g/GaSb-TO ratio decreases rapidly with the increase of substrate temperature,which suggests a small amount of crystalline Sb in the GaSb thin film and suggests that Sb atoms in the thin film decrease.In Raman spectra,the transverse optical（TO） mode intensity is stronger than that of the longitudinal optical（LO） mode,which indicates that all the samples are disordered.The LO/TO intensity ratio increases with increasing substrate temperature which suggests the improved polycrystalline quality of the GaSb thin film.A downshift of the TO and LO frequencies of the polycrystalline GaSb thin film to single crystalline bulk GaSb Raman spectra is also observed.The uniaxial stress in GaSb thin film is calculated and the value is around 1.0 GPa.The uniaxial stress decreases with increasing substrate temperature.These results suggest that a higher substrate temperature is beneficial in relaxing the stress in GaSb thin film.     

Influence of the p-type doping on the radiometric performances of MWIR InAs/GaSb superlattice photodiodes

In this paper, quantum efficiency (QE) measurements performed on type-II InAs/GaSb superlattice (T2SL) photodiodes operating in the mid-wavelength infrared domain, are reported. Several comparisons were made in order to determine the SL structure showing optimum radiometric performances: same InAs-rich SL structure with different active zone thicknesses (from 0.5 μm to 4 μm) and different active zone doping (n-type versus p-type), same 1 μm thick p-type active zone doping with different SL designs (InAs-rich versus GaSb-rich and symmetric SL structures). Best result was obtained for the p-type doped InAs-rich SL photodiode, with a 4 μm active zone thickness, showing a QE that reaches 61% at λ = 2 μm and 0 V bias voltage.     

Intersubband lifetimes in InAs/GaSb superlattices using saturated absorption spectroscopy

We investigate intersubband relaxation rates above the optical phonon energy in a InAs/GaSb superlattice using saturation spectroscopy. A high-intensity free-electron laser tuned to the intersubband transition energy is used to saturate the absorption process revealing picosecond relaxation rates. The effects of the parallel magnetic field and laser energy on the relaxation processes are explored.     

Photoconduction in amorphous thin films of Se90Sb10-xAgx glassy alloys

The present paper reports the steady state photoconductivity and photosensitivity response of thermally evaporated amorphous thin films of Se₉₀Sb_10-xAg_x(x = 2, 4, 6, 8, 10). Temperature dependence of dark conductivity is studied and activation energy is calculated for different samples. Temperature dependence of photoconductivity is also studied at different intensities. From temperature dependence of photoconductivity activation energy is computed at different intensities which are found to vary from 0.26 to 0.47 eV. Intensity dependence of photoconductivity has also been studied at different temperatures. These curves are plotted on logarithmic scale and found to be straight lines which show that photoconductivity follows a power law with intensity. Composition dependence of dark conductivity, activation energy of DC conduction and photosensitivity show that these parameters are highly. composition dependent and show a discontinuity at a particular composition when Ag concentration becomes 6 at. %. This is explained in terms of transition from floppy state to mechanically stabilized state at this composition.     

Raman properties embeddedof GaSb nanoparticlesin SiO2 films

The Raman shifts of nanocrystalline GaSb excited by an Ar^ ion laser at wavelengths 514.5, 496.5, 488.0, 476.5,and 457.9nm are studied by an SPEX-1403 laser Raman spectrometer respectively, and they are explained by phonon confinement, tensile stress, resonant Raman scattering and quantum size effects. The Stokes and anti-Stokes Raman spectra of GaSb nanocrystals strongly support the Raman feature of GaSb nanocrystals. The calculated optical spectra compare well with experimental data on Raman scattering GaSb nanocrystals.     

基于GaSb/CdS薄膜热光伏电池的器件设计

基于GaSb薄膜热光伏器件是降低热光伏系统成本的有效途径之一, 本文主要针对GaSb/CdS薄膜热光伏器件结构进行理论分析. 采用AFORS-HET软件进行模拟仿真, 分析GaSb和CdS两种材料各自的缺陷态密度、界面态对电池性能的影响. 根据软件模拟可以得知, 吸收层GaSb的缺陷态密度以及GaSb与CdS之间的界面态密度是影响电池性能的重要因素. 当GaSb缺陷态增加时, 主要影响电池的填充因子, 电池效率明显下降. 而作为窗口层的CdS缺陷态密度对电池性能影响不明显, 当CdS缺陷态密度上升4个数量级时, 电池效率仅下降0.11%.     

Intersubband transitions in InAs/GaSb semi-metallic superlattices

Magnetic field orientated parallel to the superlattice layers enables intersubband absorption to occur for normally incident light. We investigate semi-metallic InAs/GaSb superlattices in this configuration, presenting data over a wide range of InAs well widths. For narrow wells, the reduced absorption coefficient means that an alternative waveguide configuration, where the light makes about 4 or 5 passes through the sample is used. In this second configuration we see further activation of the intersubband resonance by the parallel field. The intersubband energy and absorption characteristics are studied over a large range of well widths and compared with results from 8-band k·p calculations.     

Ferromagnetic GaSb/Mn digital alloys

In order to realize spintronic devices in narrow-gap semiconductors, we have carried out studies on the well-known InAs/GaSb-based materials and structures. As a key component to such devices, GaSb/Mn digital alloys were successfully grown by molecular beam epitaxy. Good crystal quality was observed with transmission electron microscopy showing well-resolved Mn-containing layers and no evidence of 3D MnSb precipitates in as-grown samples. Ferromagnetism was observed in GaSb/Mn digital alloys with temperature-dependent hysteresis loops in magnetization up to 400 K (limited by the experimental setup). Magnetotransport studies were also carried out, both in the conventional Hall-bar configuration, and on gated Hall-bar structures. Both anomalous Hall effect and tunable ferromagnetism with applied gate bias were investigated. Annealing studies of the digital alloys reveal evidence of migration of Mn atoms at elevated temperatures.     

Thermally induced native defect transform in annealed GaSb

Undoped p-type Ga Sb single crystals were annealed at 550–600?C for 100 h in ambient antimony. The annealed Ga Sb samples were investigated by Hall effect measurement, glow discharge mass spectroscopy(GDMS), infrared(IR)optical transmission and photoluminescence(PL) spectroscopy. Compared with the as-grown Ga Sb single crystal, the annealed Ga Sb samples have lower hole concentrations and weak native acceptor related PL peaks, indicating the reduction of the concentration of gallium antisite related native acceptor defects. Consequently, the below gap infrared transmission of the Ga Sb samples is enhanced after the thermal treatment. The mechanism about the reduction of the native defect concentration and its influence on the material property were discussed.     

Al/GaSb异质结的慢正电子研究

用单能慢正电子束和 X 射线衍射方法研究了 Al/n-GaSb 金属半导体异质结在不同温度退火的情况下的演变.采用三层模型既 Al/界面/GaSb 对 S-E 实验数据进行拟合.结果发现在未退火样品的 Al 和 GaSb 之间存在一个厚度大约5nm 的界面层.在经过400℃退火后,该界面厚度增加到约400nm,且 S 参数下降.这可能是由于在退火过程中,界面区域的原子在界面处相互扩散所引起的.Al 膜的 S_(Al)参数降低且效扩散长度 L_(Al)增加,说明 Al 膜内的空位缺陷经过退火被消除且进行结构重整,晶格结构不断变好的结果.衬底 GaSb 的 S_B 参数和有效扩散长度 L_B 的演变表明,经过250℃退火后,原有的正电子捕获中心消失：但是经进一步400℃退火,又产生了新的正电子捕获中心.这可能来源于其他类型的与 V_(Ga)相关缺陷的正电子捕获以及 Ga_(Sb)晶格反位引起的正电子浅捕获.X 射线衔射的测量结果证实了正电子方法的结论.     

正电子湮没谱和光致发光谱研究掺锌GaSb质子辐照缺陷

用正电子湮没谱和光致发光谱研究了质子辐照后掺锌GaSb中的缺陷.通过分析正电子的缺陷寿命τ₂及强度I₂的变化发现,在高能质子的辐照下产生了双空位缺陷V_GaV_Sb,可能同时产生了小的空位团.正电子平均寿命τ_av和S参数随着质子辐照剂量的变化也证明了这一结论.通过分析不同质子辐照剂量下掺锌GaS     

Structural stability and electronic properties of GaSb nanowires

The structural stability and electronic properties of four different shapes of GaSb nanowire have been studied by ab-initio method using the generalized gradient approximations. The different structures were two atom linear wire, two atom zigzag wire, four atom square wire and six atom hexagonal wire. The geometry optimization and the stability of all nanowires were investigated. We explore the minimum energy atomic configuration for all the considered shapes. We find that four atom square wire configuration has greater stability in comparison to other shapes. The analysis of density of states and band structures of optimized nanowires predicts that semiconducting nanowires may be metallic or semiconducting. The behavior entirely depends upon the geometrical structure.     

Microwave cyclotron resonance of hot electrons in p-type GaSb

A microwave photocreated cyclotron resonance signal is observed in p-type GaSb in the temperature range 1–30 K. Circular polarization and other measurements identify the carriers as electrons in the (000) conduction band. The problem of a surface effect on the measured peak position, reported for the first time is avoided by bulk carrier creation. An exponential loss of signal intensity at 27 K is explained by the theory of background plasma effects. The measured ωτ of 1·5–4 yields an electron collision time of τ ～ 10^?11 sec. The scattering mechanism at liquid helium temperatures is identified as being partly due to neutral defect acceptor scattering of hot electrons, with an unidentified residual scattering process. The electron polaron effective mass is measured to be (m *(polaron)/m₀) = 0·0412 ± 0·0012 for hot electrons with an average energy of ～ 14 MeV and is isotropic within 1 per cent. When corrections for conduction-band non-parabolicity and hot polaron effects are applied, the band-edge free electron mass is calculated to be (m₀*(free)/m₀) = 0·0396 ± 0·0021 (±5·2 per cent).     

N-type GaSb single crystals with high below-band gap transmission

Te-doped GaSb single crystals are studied by measuring Hall effect, infrared(IR) transmission and photoluminescence(PL) spectra. It is found that the n-type GaSb with IR transmittance can be obtained as high as 60% by the critical control of the Te-doping concentration and electrical compensation. The concentration of the native acceptor-associated defects is apparently low in the Te-doped GaSb compared with those in undoped and heavily Te-doped GaSb. The mechanism for the high IR transmittance is analyzed by considering the defect-involved optical absorption process.     

温度对GaSb/GaAs量子点尺寸分布的影响

采用低压金属有机物化学气相沉积 (LP-MOCVD) 法制备GaSb/GaAs量子点。通过对不同生长温度的样品进行分析发现温度的变化对GaSb/GaAs量子点的相位角无明显影响,量子点的形状是透镜型。由于量子点特殊的应力分布,可实现量子点的"自限制"生长。量子点的化学势不连续性以及Ostwald熟化机制的影响使得量子点尺寸分布在一定范围内不连续,会出现两种尺寸模式的量子点生长。Sb原子的表面迁移率对GaSb/GaAs量子点生长有较大的影响。升高温度可有效改善量子点的分立性,在升温过程中量子点体现出其熟化过程,高温时表面原子的解析附作用对量子点尺寸和密度的影响较大。     

Coherent phonon dynamics in short-period InAs/GaSb superlattices

We have performed ultrafast pump-probe spectroscopy studies on a series of InAs/GaSb-based short-period superlattice (SL) samples with periods ranging from 46 Å to 71 Å. We observe two types of oscillations in the differential reflectivity with fast (∼$\sim$1–2 ps) and slow (∼$\sim$24 ps) periods. The period of the fast oscillations changes with the SL period and can be explained as coherent acoustic phonons generated from carriers photoexcited within the SL. This mode provides an alternative method for determining the SL period. The period of the slow mode depends on the wavelength of the probe pulse and can be understood as a propagating coherent phonon wavepacket modulating the reflectivity of the probe pulse as it travels from the surface into the sample.     

GaSb衬底上外延InAsxSb1-x材料的LP-MOCVD研究

采用自制的低压金属有机化学汽相淀积LP-MOCVD设备, 在(100)面GaSb单晶衬底上外延生长了InAsSb材料.用X射线双晶衍射、光学显微镜和扫描电镜、电子探针能谱仪等对材料特性进行了表征，分析研究了生长温度、Ⅴ/Ⅲ比、过渡层等对外延层的影响.并且获得了与GaSb衬底晶格失配度较低的表面光亮的晶体质量较好的InAsSb外延层.     

Interband transitions from the photoreflectance of GaSb/AlSb multiple quantum wells

We have measured the photoreflectance spectra at 77K of two GaSb/AlSb multiple quantum wells. Excellent quantitative agreement has been obtained between the experimental data and a theoretical calculation of inter-subband energies at Λ (GaSb). This agreement extends over the entire energy range where the hole states are confined and the electron states are below the X conduction band minimum of AlSb. This has made it possible to determine a conduction band offset parameter of 0.85 ± 0.08 (before strain) and the strain distribution. Deviations from the agreement beyond this energy range provide evidence for the mixing of the Λ-X states.     

Excitonic photoluminescence properties of nanocrystalline GaSb and Ga0.62In0.38Sb embedded in silica films

The GaSb and Ga_0.62In_0.38Sb nanocrystals were embedded in the SiO₂ films by radio-frequency magnetron co-sputtering and were grown on GaSb and Si substrates at different temperatures. We present results on the 10 K excitonic photoluminescence (PL) properties of nanocrystalline GaSb and Ga_0.62In_0.38Sb as a function of their size. The measurements show that the PL of the GaSb and Ga_0.62In_0.38Sb nanocrystallites follows the quantum confinement model very closely. By using deconvolution of PL spectra, origins of structures in PL were identified.