Numerical analysis of the short-circuit current density in GaInAsSb thermophotovoltaic diodes

In this paper, a simulation and analysis on the short-circuit current density (J_sc) of the P-GaSb window/P-Ga_xIn_1−xAs_1−ySb_y emitter/N-Ga_xIn_1−xAs_1−ySb_y base/N-GaSb substrate structure is performed. The simulations are carried out with a fixed spectral control filter at a radiator temperature (T_rad) of 950 °C, diode temperature (T_dio) of 27 °C and diode bandgap (E_g) of 0.5 eV. The radiation photons are injected from the front P-side. Expressions for minority carrier mobility and absorption coefficient of Ga_xIn_1−xAs_1−ySb_y semiconductors are derived from Caughey–Thomas and Adachi’s model, respectively. The P-Ga_xIn_1−xAs_1−ySb_y emitter with a much longer diffusion length is adopted as the main optical absorption region and the N-Ga_xIn_1−xAs_1−ySb_y base region contribute little to J_sc. The effect of P-GaSb window and P-Ga_xIn_1−xAs_1−ySb_y emitter region parameters on J_sc is mainly analyzed. Dependence of J_sc on thickness and carrier concentration of the window are analyzed; these two parameters need to be properly selected to improve J_sc. Contributions from the main carrier recombination mechanisms in the emitter region are considered; J_sc can be improved by suppressing the carrier recombination rate. Dependence of J_sc on the carrier concentration and layer thickness of the emitter P-region are also analyzed; these two parameters have strong effect on J_sc. Moreover, adding a back surface reflector (BSR) to the diode can improve J_sc. The simulated results are compared with the available experimental data and are found to be in good agreement. These theoretical simulations help us to better understand the electro-optical behavior of Ga_xIn_1−xAs_1−ySb_y TPV diode and can be utilized for performance enhancement through optimization of the device structure.     

0.6-eV bandgap In0.69Ga0.31As thermophotovoltaic devices with compositionally undulating step-graded InAsyP1-y buffers

Single-junction,lattice-mismatched In0.69Ga0.31As thermophotovoltaic(TPV) devices each with a bandgap of 0.6 eV are grown on InP substrate by metal-organic chemical vapour deposition(MOCVD).Compositionally undulating stepgraded InAsyP1-y buffer layers with a lattice mismatch of ～1.2% are used to mitigate the effect of lattice mismatch between the device layers and the InP substrate.With an optimized buffer thickness,the In0.69Ga0.31As active layers grown on the buffer display a high crystal quality with no measurable tetragonal distortion.High-performance single-junction devices are demonstrated,with an open-circuit voltage of 0.215 V and a photovoltaic conversion efficiency of 6.9% at a short-circuit current density of 47.6 mA/cm2,which are measured under the standard solar simulator of air mass 1.5-global(AM 1.5 G).     

Elastic constants and mechanical stability of InxAl1 − xAsySb1 − y lattice-matched to different substrates

Based on a pseudopotential approach under the virtual crystal approximation, the elastic modulus of In_xAl_1???xAs_ySb_1???y quaternaries lattice-matched to InP, GaSb and InAs substrates has been investigated. Our findings show a reasonably good accord with experiment. The dependence of the elastic features of interest on the indium concentration x shows a monotonic behaviour when In_xAl_1???xAs_ySb_1???y is lattice-matched to InP substrate. In that case, the elastic constants have larger values and the material system of interest becomes less harder and its rigidity becomes weaker. The mechanical stability criteria is verified in terms of elastic constants and shows that In_xAl_1???xAs_ySb_1???y is mechanically stable for each x and substrate being considered here. The change in indium content x and the substrate is found to have no much effect on both the Poisson ratio and machinability. The present study showed that a proper choice of the indium composition x and substrate may provide more diverse opportunities as regards the elastic modulus of In_xAl_1???xAs_ySb_1???y.     

Thickness study of Al:ZnO film for application as a window layer in Cu(In1−xGax)Se2 thin film solar cell

Structural, electrical and optical properties of Al doped ZnO (Al:ZnO) thin film of various thicknesses, grown by radio-frequency magnetron sputtering system were studied in relation to the application as a window layer in Cu(In_1−xGa_x)Se₂ (CIGS) thin film solar cell. It was found that the electrical and structural properties of Al:ZnO film improved with increasing its thickness, however, the optical properties degraded. The short circuit current density, J_sc of the fabricated CIGS based solar cells was significantly influenced by the variation of the Al:ZnO window layer thickness. Best efficiency was obtained when CIGS solar cell was fabricated with electrically and optically optimized Al:ZnO window layer.     

A simple model for optimization design of high performance In1−x−y Ga y Al x As strained MQW DFB lasers

It is well known that complex rate equations and the couple wave equation have to be solved by the method of iteration in the simulation of multi-quantum well (MQW) distributed feedback Bragg (DFB) lasers, and a long CPU time is needed. In this paper, from the oscillation condition of lasers, we propose a simple and fast model for optimization of In_1–x–y Ga _y Al _x As strained MQW DFB lasers. The well number and the cavity length of 1.55 m wavelength In_1–x–y Ga _y Al _x As MQW DFB lasers are optimized using the model. As a result, the simple model gives almost the same results as the complex one, but 90% CPU time can be saved. In addition, a low threshold, high maximum operating temperature of 550–560 K, and high relaxation oscillation frequency of over 30 GHz MQW DFB laser is presented.     

Effect of pressure on the properties of DH diode lasers in AlxGa1-xAsySb1-y/GaSb system

Abstract

A helium pressure appparatus for diode laser studies up to 1.4 GPa at 77–300 K has been developed. DH lasers with Al_xGa_1-xAs_ySb_1-y active layers (x=0-0.05) lattice-matched to GaSb substrates have been investigated. It has been shown that in lasers with x,y=0 pressure dependences of the threshold current density (J_th) and the average electron lifetime at the threshold (τ) measured at 80 K depend strongly on the quadratic recombination of L^c ₆ electrons, the characteristic coefficient being 1.5×10^?11 cm³s^?1. The pressure-composition equivalence coefficient dx/dP=2.2×10^?10 Pa^?1 has been obtained for the lowest temperatures used.     

共轭低聚物中光生分子间电荷转移态的第一性原理研究

本文基于第一性原理中的Heyd-Scuseria-Ernzerh方法研究了单层In_1-xGa_xN的电子结构和光学性质.计算得到单层In_1-xGa_xN的能带结构和态密度（DOS）,发现随着掺杂比例的变化,体系带隙的变化范围是1.8~3.8 eV,表明通过Ga的掺杂可以实现体系带隙值的调节.并且还研究了单层In_1-xGa_xN的介电函数,折射率和吸收系数等光学性质,结果表明随着Ga掺杂浓度的增加,介电函数谱的主峰和吸收谱发生了显著的蓝移.此外,基于能带结构和态密度图谱,对单层In_1-xGa_xN的光学性质进行分析,预测这种材料独特的光学性质在纳米电子学和光学器件中会有广泛的应用.     

Fermi edge singularity evidence from photoluminescence spectroscopy of AlGaAs/InGaAs/GaAs pseudomorphic HEMTs grown on (3 1 1)A GaAs substrates

InGaAs/AlGaAs/GaAs pseudomorphic high electron mobility transistor (P-HEMT) structures were grown by Molecular Beam Epitaxy (MBE) on (3 1 1)A GaAs substrates with different well widths, and studied by photoluminescence (PL) spectroscopy as a function of temperature and excitation density.The PL spectra are dominated by one or two spectral bands, corresponding, respectively, to one or two populated electron sub-bands in the InGaAs quantum well. An enhancement of PL intensity at the Fermi level energy (E_F) in the high-energy tail of the PL peak is clearly observed and associated with the Fermi edge singularity (FES). This is practically detected at the same energy for all samples, in contrast with energy transitions in the InGaAs channel, which are shifted to lower energy with increasing channel thickness. PL spectra at low temperature and low excitation density are used to optically determine the density of the two-dimensional electron gas (2DEG) in the InGaAs channel for different thicknesses. The results show an enhancement of the 2DEG density when the well width increases, in good agreement with our previous theoretical study.     

Exciton and polaron properties in GaxIn1−xAs ternary mixed crystals

Based on the pseudopotential method under the virtual crystal approximation that takes into account the effect of compositional disorder, the electron and heavy-hole effective masses and the dielectric constants in Ga_xIn_1−xAs (0≤x≤1) have been calculated. The results are firstly used in the Wannier equation, which allowed the determination of the exciton reduced mass, binding energy and Bohr radius; then, the polaron properties have been investigated. In this respect, the Fröhlich coupling parameter, Debye temperature and polaron effective mass are calculated and their dependence on the Ga concentration is examined. For InAs and GaAs, our results are generally in reasonable agreement with the known data in the literature, while for compositions x in the range 0-1, our treatment represents the first theoretical predictions. It is found that the exciton and polaron properties for compositions 0<x<1 differ from those of the parent compounds suggesting thus more diverse opportunities to describe most exciton and polaron properties in ternary mixed crystals of interest.     

Observation of sequential excited-to-excited states resonant tunneling in weakly coupled superlattices with wide quantum wells

The sequential excited-to-excited state resonant tunneling effect was observed in weakly coupled long-period superlattices resulting in additional negative differential conductivity resonances in multistable current–voltage characteristics. The results obtained show the evidence of the highly nonequilibrium distribution of carriers over subbands with energies below the optical phonon energy in superlattices. A new type of electric field domains, due to resonant tunneling between excited subbands in adjacent wells, is considered, and experimental evidencies of such a domain's existence are given.     

InGaN薄膜的紫外共振喇曼散射

利用325nm紫外光激发,对不同组分的In_xGa_1-xN薄膜的喇曼散射谱进行了研究.在光子能量大于带隙的情况下,观察到显著增强的二阶A₁(LO)声子散射峰.二阶LO声子峰都从一阶LO声子的二倍处向高能方向移动,移动量随样品In组分的增加而增大,认为是带内Frhlich相互作用决定的多共振效应引起的.分析了一阶LO声子散射频率和峰型与In组分的关系.在喇曼谱中观察到样品存在相分离现象,并与X射线衍射的实验结果进行 关键词： xGa_1-xN合金')" href="#">In_xGa_1-xN合金 紫外共振喇曼散射 二阶声子 相分离     

Electrodeposition of BixSb2−xTey thermoelectric thin films from nitric acid and hydrochloric acid systems

The electrochemical behaviors of Bi^III, Te^IV and Sb^III single ions and their mixtures were investigated in nitric acid and hydrochloric acid system separately. Based on which, Bi_xSb_2−xTe_y thermoelectric films were prepared by potentiostatic electrodeposition from the solutions with different concentrations of Bi^III, Te^IV and Sb^III in the two acid systems. The morphologies, compositions, structures, Seebeck coefficients and resistivities of the deposited thin films were characterized and compared by ESEM (or FESEM), EDS, XRD, Seebeck coefficient measurement system and four-probe resistivity measuring device respectively. The results show that although Bi_xSb_2−xTe_y thermoelectric thin film which structure is consistent with the standard pattern of Bi_0.5Sb_1.5Te₃ can be gained in both of the two acid solutions by adjusting the deposition potential, their morphologies and thermoelectric properties have big differences in different acid solutions.     

Optical and physical properties of different composition of InxSe1−x thin films

Thin film binary alloys of In_xSe_1−x (0.05?x?0.30) have been prepared by the thermal evaporation technique. The optical transmission and reflection spectrum of these films were measured in the range 300-1100 nm. Both refractive index, n and extinction coefficient k have been determined from transmission and reflection measurements in terms of Murmann's equations. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple-DiDomenico model. The width of band tail is determined and the optical absorption edge is described using the ‘non-direct transition’ model proposed by Tauc. Finally, the relationship between the optical gap and chemical composition in In_xSe_1−x amorphous system is discussed in terms of the average heat of atomization H_s and average coordination number N_c. The results of these calculations can be used rationalize the observed optical properties of these materials. Finally, the chemical bond approach has been also applied to interpret the decrease of the glass optical gap with increasing In content.     

Dispersive optical constants of a-Se100−xSbx films

Thin films of amorphous Se_100−xSb_x (x=5,10 and 20 at%) system are deposited on a silicon substrate at room temperature (300 K) by thermal evaporation technique. The optical constant such as refractive index (n) has been determined by a method based on the envelope curves of the optical transmission spectrum at normal incidence by a Swanpoel method. The oscillator energy (E_o), dispersion energy (E_d) and other parameters have been determined by the Wemple–DiDomenico method. The absorption coefficient (α) has been determined from the reflectivity and transmitivity spectrum in the range 300–2500 nm. The optical-absorption data indicate that the absorption mechanism is a non-direct transition. We found that the optical band gap, E_g^opt, decreases from 1.66±0.01 to 1.35±0.01 eV with increase Sb content.     

Theoretical research on optical properties and quantum efficiency of Ga1−xAlxN photocathodes

In order to design the optimal component structure of transmission-mode (t-mode) Ga_1−xAl_xN photocathode, the optical properties and quantum efficiency of Ga_1−xAl_xN photocathodes are simulated. Based on thin film principle, optical model of t-mode Ga_1−xAl_xN photocathodes is built. And the quantum efficiency formula is put forward. Results show that Ga_1−xAl_xN photocathodes can satisfy the need of detectors with “solar blind” property when the Al component is bigger than 0.375. There is an optimal thickness of Ga_1−xAl_xN layer to get highest quantum efficiency, and the optimal thickness is 0.3 μm. There is close relation between absorptivity and quantum efficiency, which is in good agreement with the “three-step” model. This work gives a reference for the experimental research on the Ga_1−xAl_xN photocathodes.     

Compare of the electronic structures of F- and Ir-doped SmFeAsO

The electronic structures of Fe-based superconductor SmFeAsO_1−xF_x and SmFe_1−yIr_yAsO are compared through X-ray photoemission spectroscopy in this study. With fluorine or iridium doping, the electronic structure and chemical environment of the SmFeAsO system were changed. The fluorine was doped at an oxygen site which introduced electrons to a reservoir Sm–O layer. The iridium was doped at an Fe site which introduced electrons to a conduction Fe–As layer directly. In a parent material SmFeAsO, the magnetic ordering corresponding to Fe3d in the low-spin state is suppressed by both fluorine and iridium doping through suppressing the magnetism of 3d itinerant electrons. Compared to fluorine doping, iridium doping affected superconductivity more significantly due to an iridium-induced disorder in FeAs layers.     

Short-range order analysis and some physical properties of InxSe1−x glasses

Bulk In_xSe_1−x (with x=5-25 at%) glasses were prepared using the melt-quench technique. Short range order(SRO) was examined by the X-ray diffraction using Cu(k_α) radiation in the wave vector interval 0.28≤k≤6.5 A⁰⁻¹.The SRO parameters have been obtained from the radial distribution function. The inter-atomic distance obtained from the first and second peak are r₁=0.263 and r₂=0.460 nm, which is equivalent In-Se and Se-Se bond length. The fundamental structural unit for the studied glasses is In₂Se₃ pyramid. Using the differential scanning calorimetry (DSC), the crystallization mechanism of In_xSe_1−x chalcogenide glass has been studied. The glass transition activation energy (E_g) is 289±0.3 kj/mol.There is a correlation amongst the glass forming ability, bond strength and the number of lone pair electrons. The utility of the Gibbs-Di Marzio relation was achieved by estimating T_g theoretically.     

Electrical resistivity study on SmSe1−x As x under pressure

Electrical resistivity measurements under pressure and lattice parameter study on SmSe_1−x As _x are reported here. The estimate d lattice parameter and valence is calculated for the same and they are found to be in good agreement with the experimental data. The electrical conductivity increases with the increase of As concentration. An erratum to this article is available at .     

Electronic structure of Ga1−xCrxN investigated by photoemission spectroscopy

We have obtained the Cr 3d-like energy states, which located in the band gap of GaN by means of resonant photoemission spectroscopy. In the difference spectrum between the valence band photoemission spectra of non-doped GaN and that of the Ga_0.937Cr_0.063N, we observed the new energy state, in band gap, consists of Cr 3d-like and N 2p-like component by strong hybridization.     

InAs/GaAs和InAs/InxGa1-xAs/GaAs纳米线异质结构的生长研究

利用金辅助金属有机化学气相沉淀法(MOCVD)在GaAs(111)B衬底上分别制备了InAs/GaAs和InAs/In _{x Ga1-xAs/GaAs(0≤x≤1)纳米线异质结构.实验结果显示,直接生长在GaAs纳米线上的InAs纳米线生长方向杂乱或者沿着GaAs纳米线侧壁向衬底方向生长,生长的含有In x Ga1-xAs组分渐变缓冲段的InAs/In x Ga1-x关键词： 纳米线异质结构 xGa1-xAs')" href="#">InxGa1-xAs 组分渐变缓冲层 金属有机化学气相沉淀法}