Comparison of InGaSb/InAs superlattice structures grown by MBE on GaSb, GaAs, and compliant GaAs substrates

This paper contains the characterization results for indium arsenide/indium gallium antimonide (InAs/InGaSb) superlattices (SL) that were grown by molecular beam epitaxy (MBE) on standard gallium arsenide (GaAs), standard GaSb, and compliant GaAs substrates. The atomic force microscopy (AFM) images, peak to valley (P-V) measurement, and surface roughness (RMS) measurements are reported for each sample. For the 5 μm×5 μm images, the P-V heights and RMS measurements were 37 ? and 17 ?, 12 ? and 2 ?, and 10 ? and 1.8 ? for the standard GaAs, standard GaSb, and compliant GaAs respectively. The high resolution x-ray diffraction (HRXRD) analysis found different 0^th order SL peak to GaSb peak spacings for the structures grown on the different substrates. These peak separations are consistent with different residual strain states within the SL structures. Depending on the constants used to determine the relative shift of the valance and conduction bands as a function of strain for the individual layers, the change in the InAs conduction band to InGaSb valance band spacing could range from +7 meV to −47 meV for a lattice constant of 6.1532 ?. The cutoff wavelength for the SL structure on the compliant GaAs, control GaSb, and control GaAs was 13.9 μm, 11 μm, and no significant response, respectively. This difference in cutoff wavelength corresponds to approximately a −23 meV change in the optical gap of the SL on the compliant GaAs substrate compared to the same SL on the control GaSb substrate.     

用液相外延法生长3～7μm波段InAs/InAs1-ySby及其光学和电学性质

用液相外延(LPE)法在InAs衬底上生长了3～7μm波段的InAs1-ySby外延层,研究了外延多层的组份与禁带宽度和晶格常数的关系。用光学显微镜、傅立叶变换红外(FTIR)透射、光荧光(PL)谱测试以及偏振光椭圆仪研究了外延材料的光学特性。电学性质是将计算值与实测有效霍尔(Hall)参数的厚度关系拟合得到的。结果表明,本文生长的材料在中红外光伏型探测器上具有良好的应用前景。     

Modulation spectroscopy study of a strained layer GaAs/GaAsP multiple quantum well structure

Using contactless electroreflectance (CER) and piezoreflectance at 300 K we have characterized a GaAs/GaAs_1?xP_x multiple quantum well (MQW) structure, “GaAs” (nominal) and GaAsP epilayers grown by chloride transport chemical vapor deposition on GaAs (001) substrates. From a detailed lineshape fit to the CER data from the epilayers we have determined the energies of the fundamental band gap and hence the phosphorous composition. The nominal “GaAs” epilayers were found to have phosphorous compositions of about 2.5–3.2%, a result of the phosphorous diffusion between growth chambers in the reactor. The GaAs_1?xP_x epilayer had x=0.29. For the GaAs_0.97P_0.03/GaAs_0.71P_0.29MQW comparison between the experimentally observed energies of a number of quantum transitions with a theoretical envelope function calculation, including the effects of strain in the barriers, made it possible to evaluate the unstrained conduction band offset parameter Q_c=0.50±0.05. Our value for this parameter is discussed in relation to other works. Atomic force microscopy was employed to investigate the surface morphology of the 230 Å GaAsP top layer of the MQW in addition to a 2000 Å GaAsP epilayer. From the absence of any cross-hatch pattern associated with misfit dislocations on the former we concluded that the GaAsP in the MQW is pseudomorphic. On the other hand the 2000 Å epilayer exhibited signs of strain relaxation.     

Large-area uniform OMVPE growth for GaAs/AIGaAs quantum-well diode lasers with controlled emission wavelength

The properties of GaAs and AlGaAs epilayers grown in a vertical rotating-disk OMVPE reactor operated at reduced pressure (0.2 atm) are extremely uniform. For substrate rotation at 500 rpm, the thickness uniformity is ±1% for thick epilayers and ±2% for quantum wells 3−10 nm thick. The coefficient of variation in aluminum composition is 1.8 × 10⁻³ or less. For broad-area GRIN-SCH diode lasers containing a single-quantumwell active layer, the threshold current density and differential quantum efficiency are highly uniform. The laser emission wavelength is precisely controlled by adjusting the active layer thickness and composition. For 175 devices distributed over a 16-cm² wafer containing a 10-nm-thick Al_0.07Ga_0.93As active layer, the total variation in emission wavelength is 3.0 nm. For all of these devices and for test devices from nine additional wafers, the wavelengths range from 803.5 to 807.4 nm.     

An AlGaAs-GaAs dual-wavelength photodetector with 500 Å resolution

An Au-(N)Al_0.07Ga_0.93As-(n)GaAs Schottky barrier dual-wavelength photodetector with 500 Å resolution has been developed. By varying the reverse bias, the photothreshold of the detector can be changed from 0.82 to 0.87 μm. The diode can thus be applied to demultiplex two optical signals with respective wavelengths of 0.8 and 0.85 μm. This provides a useful detector for use in a dual-channel optical communication system. The principle is based on the band readjustment effect which is due to the interaction of the closely-spaced Au-AlGaAs Schottky barrier and the AlGaAs-GaAs heterojunction.     

On the conduction-band structure of bismuth telluride: optical absorption data

The optical absorption spectra of n-Bi₂Te₃ in the range 40–300 meV are studied at room temperature in relation to the electron concentration and sample thickness in order to determine the parameters of the additional subband in the conduction band of Bi₂Te₃ and to clarify the possible effect of this subband on charge-carrier transport. It is shown that bismuth telluride is a direct-gap semiconductor with an additional subband in the conduction band. These data are consistent with the results of studies of quantum oscillations in n-Bi₂Te₃ in high magnetic fields at temperatures below 20 K.     

室温InAsSb长波红外探测器的研制

用熔体外延法(ME)生长出厚度达到100μm的InAsSb外延层,截止波长进入8～12μm波段。测量结果表明,InAsSb材料具有良好的单晶取向和结晶质量,位错密度达到104cm-2量级。室温下,霍尔测量得到的载流子浓度为1～3×1016cm-3,电子迁移率大于5×104cm2/Vs。用此材料制得了2～9μm波段的高灵敏度In-AsSb室温红外探测器。该探测器为浸没型光导元件,安装了镀有SiO或ZnS增透膜的单晶Si光学透镜。在黑体温度为500K、黑体调制频率为800 Hz和外加偏置电流为10 mA的测试条件下,测得293K下该探测器的最高黑体响应度达到168V/W,黑体探测率为2～6×108cm·Hz1/2·W-1,峰值探测率大于1×109cm·Hz1/2·W-1。     

Optically stimulated intersubband absorption in undoped amorphous Si/SiO2 qiantum well

Intersubband absorption has been observed in undoped amorphous multiple-quantum-well (MQW) strucctures under interband excitation. The transitions take place between the first and second subbands of the conduction band and involve non-equilibrium electrons excited into the first subband by optical pumping. The absorption band FWHM of 0.1 eV is much larger than for crystalline MQWs, a fact which reflects the relaxation of the electron momentum conservation in the QW plane. The high joint density of states and oscillator strength for the intersubband transitions in amorphous QWs allow one to observe the absorption at low electron concentrations (N_e ≈ 10¹³ cm^?3) in the ground conduction subband.     

长波InAsSb材料的结构特性研究

用熔体外延(ME)法在InAs衬底上生长了InAsSb外延层,用扫描电子显微镜(SEM)观察了样品的横截面,并测量出外延层的厚度达到100μm,用X-射线衍射(XRD)谱研究了InAsSb外延层的结构性质。测量结果表明,InAs/InAs0.023Sb0.977单晶具有相当完美的晶体取向结构及良好的结晶质量,这可能得益于100μm的外延层厚度基本消除了外延层与衬底之间晶格失配的影响。电子探针微分析(EPMA)测量的元素分布图像显示,Sb(锑)元素在外延层中的分布相当均匀。     

Spin-orbit splitting dependent resonant third-order nonlinear optical susceptibility in InGaN/GaN multiple quantum wells

For the transition between valence band and conduction band, the third-order nonlinear optical susceptibility χ⁽³⁾ for degenerated four-wave mixing in In_xGa_1−xN/GaN multiple quantum wells (MQWs) has been calculated. The contributions of spin-orbit split-off energy to the resonant third-order nonlinear optical susceptibility of the modes, whose polarization is vertical to the [0 0 1] direction of the MQWs, are discussed in detail. The correlations between the peaks of χ⁽³⁾, which are due to the transitions from the spin-orbit split-off energy level to first conduction subband, and the width of the quantum well and the constituents of the semiconductor material are obtained.     

Comparison of normal and inverted band structure HgTe/CdTe superlattices for very long wavelength infrared detectors

The type III band alignment of HgTe/CdTe superlattices leads to the interesting possibility of achieving very long wavelength infrared (VLWIR) (15 μm and longer) cutoff wavelengths with either normal (HgTe layer thickness less than about 70 ? for CdTe layer thickness of 50 ?) or inverted (HgTe thickness greater than about 70 ?) band structures. The inverted band structure superlattices promise even greater cutoff wavelength control than the normal band structure ones. However, the electronic band gaps of inverted band structure superlattices are substantially less than their optical band gaps, leading to large thermal carrier concentrations even at temperature as low as 40 K. These high carrier concentrations in turn give rise to more rapid Auger recombination than normal band structure superlattices with the same cutoff wavelengths. We conclude that the highest performance is expected from VLWIR HgTe/CdTe superlattice-based detectors with normal band structure absorber layers.     

InAsSb/InAsSbP diode lasers with separate electrical and optical confinement, emitting at 3–4 µm

Diode lasers based on InAsSb/InAsSbP with separate electrical and optical confinement, emitting in the wavelength interval 3–4 μm, are investigated. The lasers attain a higher operating temperature when electrical confinement is created by means of type-II heterojunctions. Interface Auger recombination is suppressed in lasers of this type, and the experimental current density is close to the theoretically calculated value for the case of predominant volume Auger recombination at a temperature of 180–220 K. Fiz. Tekh. Poluprovodn. 31, 976–979 (August 1997)     

The quantum Hall effect in a wide p-Ge1−x Six/Ge/p-Ge1−x Six potential well

Quantum magnetotransport is investigated in a series of selectively doped p-type (Ge_1?x Si_x/Ge)×N multilayered structures with Ge layer widths from 100 to 250 Å in fields up to 35 T at 1.5–4.2 K. The plots of the magnetic-field dependence of the longitudinal (ρ _xx) and Hall (ρ _xy) magnetoresistance, as well as the ratio between the oscillation periods in strong and weak fields, vary significantly in samples with wide Ge layers and (or) with a high density of the two-dimensional gas. These features can be attributed to the participation of an additional subband in carrier transport. It follows from calculations of the structure of the Ge valence band under the conditions of size quantization and quantization by a magnetic field (performed in the approximation of an infinite rectangular potential well) that the additional subband can be the second heavy-hole quantum-well subband. Estimates of its population correlate with the experimental manifestations of the participation of the additional subband in galvanomagnetic phenomena.     

Single-mode InAsSb/InAsSbP laser (λ≈3.2 μm) Tunable over 100 Å

A report is presented on the development of a single-mode laser based on the InAsSb/InAsSbP double heterostructure and operating at wavelengths of 3.2–3.3 μm in a temperature range of 12–90 K. The single-mode regime is assumed to be realized due to a smooth optical waveguide formed across the laser cavity in which the radiation flux oscillates and maintains its oscillations and intensity. An analysis is made of the effect of the current-induced shifts of the lasing frequency and the peak of the gain spectrum on the probability of single-mode lasing. Experiments were made on the scanning of OCS, NH₃, CH₃Cl, and H₂O gas media with radiation of the given laser in the frequency range with a record width of 10 cm⁻¹ (104 ?). __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 2, 2000, pp. 243–248. Original Russian Text Copyright ? 2000 by Danilova, Imenkov, Kolchanova, Civis, Sherstnev, Yakovlev.     

A small-molecule organic semiconductor

The electrical conductivity and optical properties of bis-diethylaminokumarin have been investigated. The electrical conductivity of the compound exhibited three-dimensional hopping conduction in the temperature range 295–321 K. The compound shows a typical semiconductor property, and its semiconducting property results from delocalization of the π-electrons in the structure. To determine the optical band gap of the compound, an optical absorption study was made in the wavelength range 250–600 nm. The optical study revealed that the optical transition is the allowed indirect one. The electronic parameters, such as the electrical conductivity at room temperature σ₂₅, activation energy E, and optical band gap E_g of the compound are 1.46×10^?5 S/cm, 0.42 eV, and 2.46 eV, respectively. These values are in agreement with electronic parameters of organic semiconductors.     

Mechanism of the subband excitation of photoluminescence from erbium ions in silicon under high-intensity optical pumping

The photoluminescence (PL) excitation spectra of erbium and band-to-band silicon in Si:Er/Si epitaxial structures under high-intensity pulsed optical excitation are studied. It is shown that the nonmonotonic dependence of the PL intensity on the excitation wavelength ??_ex near the absorption edge of silicon is due to inhomogeneity in the optical excitation of the Si:Er active layer. The sharp rise in the erbium PL intensity in the spectral range ??_ex = 980?1030 nm is due to an increase in the excited part of the Si:Er emitting layer on passing to subband light pumping (??_ex > 980 nm) with a low absorption coefficient in silicon because of the effective propagation of the excitation light in the bulk of the structures under study. It is shown that, under the subband optical pumping of Si:Er/Si structures, as also in the case of interband pumping, the exciton mechanism of erbium ion excitation is operative. Excitons are generated under the specified conditions as a result of a two-stage absorption process involving impurity states in the band gap of silicon.     

非制冷型中长波铟砷锑探测器

工作在中、长波红外波段(波长5~12μm)的红外探测器在红外制导、红外成像、环境监测及资源探测等方面有着重要而广阔的应用前景。目前中国军用和民用对这一波段的非制冷型、快速响应的光子型红外探测器有迫切需求。文中用熔体外延(ME)法在InAs(砷化铟)衬底上生长的InAs0.05Sb0.95(铟砷锑)厚膜单晶,制作了高灵敏度、非制冷型、中长波光导型探测器,探测器上安装了Ge(锗)浸没透镜。傅里叶变换红外(FTIR)吸收光谱显示InAsSb材料的本征吸收边出现在波长8μm以后。InAs0.05Sb0.95探测器的光谱响应波长范围为2~9μm。室温下,在波长6.5μm处的峰值探测率Dλp*达到5.4×109 cm·Hz1/2·W-1,在波长8.0μm和9.0μm处的探测率D*分别为9.3×108和1.3×108 cm·Hz1/2·W-1,显示了InAsSb探测器的优越性能及对红外探测和成像的应用前景。     

OMVPE regrowth of CH3I-vapor-etched GaAs

In experiments on the interrupted growth of GaAs by organometallic vapor phase epitaxy (OMVPE), we have compared the properties of two types of epilayers: those grown on CH₃I-vapor-etched first epilayers and those grown on first epilayers that were either untreated or etched with H₂SO₄. The OMVPE growth and CH₃I etching were performed in two different reactors, and each sample was briefly exposed to air immediately before being placed in the OMVPE reactor for growth of the second epilayer. For CH₃I etch temperatures below 500° C, the two types of second epilayers are comparable in surface morphology, as characterized by Nomarski interference microscopy, and in optical quality, as characterized by low-temperature photoluminescence measurements. Electrical characterization by C-V depth profiling shows that electron accumulation at the regrowth interface is increased very little by CH₃I etching. Such etching prior to regrowth eliminates most of the electron accumulation resulting from H₂SO₄ etching of the first epilayer.     

Electronic band structure and optoelectronic properties of double perovskite Sr2MgMoO6 through modified Becke-Johnson potential

The crystal structure, electronic and optical properties of double perovskite Sr₂MgMoO₆ have been calculated by using the full-potential linear augmented plane wave (FP-LAPW) method. The band structure and density of states (DOS) were carried out by the modified Becke–Johnson (mBJ) exchange potential approximation based on the density functional theory (DFT). The calculated band structure shows a direct band gap (Γ–Γ) of 2.663 eV for Sr₂MgMoO₆. The compound Sr₂MgMoO₆ has a triclinic structure with the space group I-1, the lattice parameters a=5.5666 Å, b=5.5661 Å and c=7.9191 Å, which are used in our calculations. The optical parameters, like dielectric constant, refractive index, reflectivity and energy loss function were also calculated and analyzed. This work provides the first quantitative theoretical prediction of the optical properties and electronic structure for the triclinic phase of Sr₂MgMoO₆.