Effects of GaAs buffer layer and lattice-matching on deep levels in Zn(S)Se/GaAs heterostructures

The effects of GaAs buffer layer and lattice-matching on the nature of deep levels involved in Zn(S)Se/GaAs heterostructures are investigated by means of deeplevel transient spectroscopy (DLTS). The heterojunction diodes (HDs) where nZn(S)Se is grown on p⁺-GaAs by metalorganic vapor phase epitaxy are used as a test structure. The DLTS measurement reveals that when ZnSe is directly grown on a GaAs substrate, there exist five electron traps A-E at activation energies of 0.20, 0.23, 0.25, 0.37, and 0.53 eV, respectively. Either GaAs buffer layer and lattice-matching may reduce the incorporation of traps C, D, and E, implying that these traps are ascribed to surface treatment of GaAs substrate and to lattice relaxation. Concentration of trap B, which is the most dominant level, is proportional to the donor concentration. However, in the ZnSSe/GaAs sub. HD, another trap level, instead of trap B, locates at the almost same position as that of trap B, and it shows anomalous behavior that the DLTS peak amplitude changes drastically as changing the rate windows. This is explained by the defect generation through the interaction between sulfide and a GaAs substrate surface. For the trap A, the concentration is a function of donor concentration and lattice mismatch, and the origin is attributed to a complex of donor induced defects and dislocations.     

Interface trap and interface depletion in lattice-mismatched GaInAs/GaAs heterostructures

The effects of lattice mismatch on the deep traps and interface depletion have been studied for the Ga_0.92In_0.08As(p⁺)/GaAs(N) and Ga_0.92In_0.08As(n)/GaAs(SI) heterostructures grown by molecular beam epitaxy. We have used deep level transient spectroscopy (DLTS) and admittance spectroscopy (AS) and observed two hole traps, one at an energy ranging from 0.1 to 0.4 eV and the other at 0.64 eV, and two electron traps at 0.49 and 0.83 eV in the GalnAs/GaAsp ⁺-N junction sample. The hole trap appeared as a broad peak in the DLTS data and its energy distribution (0.1 ∼ 0.4 eV) was obtained by a simulation fitting of the peak. Concentration of this distributed hole trap increased as the in-plane mismatch increased, suggesting its relation to defects induced by lattice relaxation, whereas the other traps are from the bulk. The misfit dislocations are believed to be responsible for the interface trap. For the Ga_0.92In_0.08As(n)/GaAs(SI) samples, Hall effect measurements showed an increased interface depletion width of about 0.14 Μm for the 0.5 Μm thick layer and about 0.12 /gmm for the 0.25 Μm thick layer, while a corresponding GaAs/GaAs sample had only 0.088 Μm for the interface depletion width.     

Role of interface chemistry and growing surface stoichiometry on the generation of stacking faults in ZnSe/GaAs

The existence of Zn-As and vacancy-contained Ga-Se interfacial layers are suggested by transmission electron microscopy of Zn-and Se-exposed (or - reacted) ZnSe/GaAs interfaces, respectively. A very low density of faulted defects in the range of ∼10⁴cm² was obtained in samples with Zn passivation on an Asstabilized GaAs-(2 × 4). However, the density of As precipitates increases as the surface coverage of c(4 × 4) reconstruction increased on the Zn-exposed Asstabilized GaAs-(2 × 4) surface and this is associated with an increase of the density of extrinsic-type stacking faults bound by partial edge dislocations with a core structure terminated on additional cations. On the other hand, densities of extrinsic Shockley-and intrinsic Frank-type stacking faults are of ∼5 × 10⁷/cm² in samples grown on Se-exposed Ga-rich GaAs-(4 × 6) surfaces. Annealing on this Se-exposed Ga-rich GaAs-(4 × 6) generated a high density of vacancy loops (1 × 10⁹/cm²) and an increase of the densities of both Shockley-and Frank-type stacking faults (>5 × 10⁸/cm²) after the growth of the films. Furthermore, we have studied the dependence of the generation and structure of Shockley-type stacking faults on the beam flux ratios in samples grown on Zn-exposed As-stabilized GaAs-(2 × 4) surfaces. Cation-and anion-terminated extrinsic-type partial edge dislocations were generated in samples grown under Zn-and Se-rich conditions, respectively. However, an asymmetric distribution on defect density under varied beam flux ratios (0.3 ≤ P_Se/P_Zn ≤ 10) is obtained.     

InGaAs／GaAs异质结构材料及器件应用

概述了ＩｎＧａＡｓ／ＧａＡｓ异质结构材料用于制作微波器件的优越性，叙述了材料的ＭＢＥ生长、输运特性和掺杂分布，以及用于制作Ｋｕ波段低噪声高增益ＨＦＥＴ的结果：栅长０．５μｍ，１２ＧＨｚ下噪声系数０．９３ｄＢ，相关增益９ｄＢ。     

Reversible electrical properties of LEC GaAs

Undoped, low-pressure, liquid-encapsulated Czochralski GaAs can be reversibly changed from conducting (ρ ∼ 1Ω-cm) to semi-insulating (ρ ∼ 10⁷Ω-cm) by either slow or fast cooling, respectively, after a 5 hr, 950° C soak in an evacuated quartz ampoule. The semi-insulating wafers are very uniform and lead to tight threshold-voltage control in direct-implant MESFET’s. We have studied crystals in both states by temperature-dependent Hall effect, photoluminescence, IR absorption, mass spectroscopy, and DLTS. It is shown that donor and acceptor concentrations are typically more than an order of magnitude greater than the C and Si concentrations, which are both less than 3 × 10¹⁴ cm⁻³. The EL2 concentration remains relatively constant at about 1.0 × 10¹⁶ cm⁻³. Thus, the normal EL2-Si-C compensation model does not apply. The most likely explanation for the reversibility involves a delicate balance between native-defect donors and acceptors in equilibrium at 950° C, but with the donors dominating after a slow cool, and the acceptors after a fast cool. A consistent model includes a dominant donor at E_c 0.13eV, probably V_As – As_Ga, and a dominant acceptor at E_v + 0.07eV, probably V_Ga Ga_As. In this model, vacancy motion is very important during the slow cool. Such processes must be strongly considered in the growth of bulk, high-purity GaAs.     

Surface treatment of znse substrate and homoepitaxy of znse

High quality ZnSe(100) substrates have been used for homoepitaxial growth by molecular beam epitaxy. A chemical pretreatment suitable for ZnSe substrate preparation is determined from x-ray photoemission spectroscopy studies. Thermal cleaning processes for the ZnSe(100) surface were investigated by insitu reflection high energy electron diffraction and the surface phase diagram for ZnSe(100) was obtained for the first time. The low temperature photoluminescence spectra recorded from homoepitaxial layers exhibit unsplit free and bound exciton transitions with strong intensities. The full widths at half maximum of the (400) x-ray diffraction spectra for ZnSe homoepitaxial layer were 17≈31 arcsec.     

Influence of Ga vs As prelayers on GaAs/Ge growth morphology

The surface morphology of GaAs films grown on Ge substrates is studied by scanning force microscopy. We find a dramatic difference arising from Ga as opposed to As prelayers in the formation of anti-phase boundaries (APBs), surface features near threading dislocations, and surface roughness, for films as thick as 1 μm. Ga prelayer samples are smooth; thin films display some APBs with predominantly one growth domain while the 1 μm thick film displays the morphology of a homoepitaxial GaAs film. In contrast, As prelayer samples are rough with complicated APB structures, which can be attributed to the increase in single steps during As₂ deposition.     

Cathodoluminescence spectroscopy of deep defect levels at the ZnSe/GaAs interface with a composition-control interface layer

In this work we investigate ZnSe/GaAs heterostructures with an additional 2 nm controlled interfacial layer (CIL) of Se- or Zn-rich composition to modify the band offset. The samples are analyzed as a function of annealing temperature by cathodoluminescence spectroscopy. The as-prepared samples show defect luminescence at ∼ 0.9 eV. With staged annealing at increasing temperatures, both the Zn-rich as well as the Se-rich interfacial layer exhibits luminescence at ∼ 1.9 eV, indicative of defect formation with an onset temperature of ∼400°C. Excitation-dependent spectroscopy provides evidence for defect formation near the interface, which extends into the ZnSe epilayer at higher temperatures. Compared to earlier work, where the threshold temperature for defect formation in bulk samples fabricated under Se-rich growth conditions occurs at temperatures as low as 325°C, the resistance to defect formation has now been improved to that of stoichiometric ZnSe. These results demonstrate that epitaxially grown CILs provide a means to alter ZnSe/GaAs band offsets without degrading the heterojunction’s resistance to defect formation at elevated temperatures.     

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.     

MBE CdTe／GaAs光致发光研究

在１０Ｋ低温下对分子束外延（ＭＢＥ）生长的ＣｄＴｅ（１１１）Ｂ／ＧａＡｓ（１００）／ＣｄＴｅ（２１１）Ｂ／ＧａＡｓ（２１１）Ｂ外延膜进行了光致发光（ＰＬ）测量，得到了ＰＬ谱和带边激子辐射的精细结构．计算得到束缚激子的半峰宽（ＦＷＨＭ）分别为０．２～０．ｓｍｅＶ和１～２ｍｅＶ．实验结果表明外廷膜的质量和生长工艺均良好．     

Optical properties of Cl-doped ZnSe epilayers grown on GaAs substrates

We have determined the optical properties of a series of Cl-doped ZnSe epilayers grown on GaAs substrates using ellipsometry and prism coupling. Initially, the carrier concentrations were determined using Hall measurements for samples between 6.30×10¹⁶ cm⁻³ and 9.50×10¹⁸ cm⁻³. Using a variable angle spectroscopic ellipsometer in the energy range between 0.7 eV and 6.5 eV, we then obtained experimental spectra for each of the samples. By incorporating a three-layer model to simulate the experimental data, we determined the complex dielectric functions for these Cl-doped ZnSe epilayers. In order to facilitate this modeling procedure, we have complemented the ellipsometric results with prism coupling experiments that measured the film thickness and the index of refraction (at discrete wavelengths) very precisely. For the fundamental band gap, we observe a blue shift with respect to the doping concentration, which can be explained by the Burstein-Moss effect. In addition, we have determined the critical point parameters related to these specimens by fitting the second derivatives of both the real and the imaginary parts of the dielectric functions. Similar to several doped III-V semiconductors reported thus far, we find that in Cl-doped ZnSe epilayers, both E₁ and E₁ + Δ ₁ red shift, as well as a broadening with respect to the doping concentration.     

Ni-Au/AlN/Si器件的深能级瞬态谱研究

对GaN器件制备过程中AlN缓冲层相关的电活性缺陷进行了C-V和深能级瞬态谱(DLTS)研究。C-V研究结果表明,制备态Ni-Au/AlN/Si MIS器件中,靠近AlN/Si界面处的掺杂浓度为4.4×10¹⁷cm-3,明显高于Si衬底的1.4×10¹⁶cm-3,意味着制备态样品中Al原子已经向衬底硅中扩散。采用退火工艺研究了GaN器件制备过程中的热影响以及热处理前后电活性缺陷在硅衬底中的演变情况,发现退火处理后,Al原子进一步向衬底硅中更深处扩散,扩散深度由制备态的500nm左右深入到1μm附近。DLTS研究结果发现,在Si衬底中与Al原子扩散相关的缺陷为Al-O配合物点缺陷。DLTS脉冲时间扫描表明,相比于制备态样品,退火态样品中出现了部分空穴俘获时间常数更大的缺陷,退火处理造成了点缺陷聚集,缺陷类型由点缺陷逐渐向扩展态缺陷发展。     

Compositional inhomogeneity at the epitaxial layer and substrate interface of AlGaAs/GaAs heterostructures

Carrier concentration spikes at the epilayer/substrate interface were observed in some two-dimensional electron gas AIGaAs/GaAs structures grown by low pressure organometallic vapor phase epitaxy. Using secondary ion mass spectroscopy, the carrier spikes were correlated with indium. Under certain growth conditions an anomalous interfacial layer, which is compositionally inhomogeneous, is formed producing an enhanced carrier density. Procedures are described which reduce the presence of indium at the epilayer/substrate interface and eliminate the carrier spike.     

Znse/GaAs超晶格的电子态和芯态激子

本文用半经验紧束缚法计算了ZnSe/GaAs(001)超晶格的能带结构,研究了其能隙与有效质量随层厚的变化.计算了(ZnSe)_5/(GaAs)_5超晶格中与杂质有关的芯态激子,其结果能说明相应异质结中束缚在Ga上的激子峰.本文还提出了该材料中导带底存在界面态.     

Electrical properties and spectra of deep centers in GaN p-i-n rectifier structures

GaN p-i-n rectifiers with 4 μm thick i-layers show typical reverse breakdown voltages of 100–600 V. We have studied the temperature dependence of current-voltage characteristics in these diodes, along with hole diffusion lengths and the deep level defects present. Generally we find that i-layer background doping varies significantly (from <10¹⁴ cm⁻³ to 2–3×10¹⁶), which influences the current conduction mechanisms. The hole diffusion lengths were in the range 0.6–0.8 μm, while deep level concentrations were ∼10¹⁶ cm⁻³.     

C_(70)/GaAs异质结的电学性质

在高真空系统中 ,将 C70 膜淀积在 n-和 p- Ga As(10 0 )衬底上 ,制成 C70 / n- Ga As和 C70 / p- Ga As两种接触 ,并对它们的电学性质作了研究 .结果发现两种接触均为强整流结 ,在偏压为± 1V时 ,C70 / n- Ga As和 C70 / p- Ga As接触的整流比分别大于 10 6 和 10 4,并且它们的理想因子都接近于 1.当正向偏压固定时 ,它们的电流均是温度倒数的指数函数 ,从中确定两种异质结的有效势垒高度分别为 0 .784和 0 .5 31e V .用深能级瞬态谱 (DL TS)在 C70 / Ga As界面上观察到电子陷阱 E(0 .6 40 e V )和空穴陷阱 H3(0 .82 2 e V) ,以及用电容 -时间 (C- t)     

MBE生长InGaAs／GaAs应变层单量子阱激光器结构材料的研究

采用ＶａｒｉａｎＧｅｎⅡＭＢＥ生长系统研究了ＩｎＧａＡｓ／ＧａＡｓ应变层单量子阶（ＳＳＱＷ）激光器结构材料。通过ＭＢＥ生长实验，探索了Ｉｎ＿ｘＧａ＿（１－ｘ）ｔＡｓ／ＧａＡｓＳＳＱＷ激光器发射波长（λ）与Ｉｎ组分（ｘ）和阱宽（Ｌ＿ｚ）的关系，并与理论计算作了比较，两者符合得很好。还研究了材料生长参数对器件性能的影响，主要包括：Ⅴ／Ⅲ束流比，量子阱结构的生长温度Ｔ＿ｇ（ＱＷ），生长速率和掺杂浓度对激光器波长、阈值电流密度、微分量子效率和器件串联电阻的影响。以此为基础，通过优化器件结构和ＭＢＥ生长条件，获得了性能优异的Ｉｎ＿（０．２）Ｇａ＿（０．８）Ａｓ／ＧａＡｓ应变层单量子阱激光器：其次长为９６３ｎｍ，阈值电流密度为１３５Ａ／ｃｍ￣２，微分量子效率为３５．１％。     

分子束外延生长InGaAs/GaAs异质结及其在独特场效应晶体管中的应用

用分子束外延技术生长了ＩｎＧａＡｓ／ＧａＡｓ异质结材料,并用ＨＡＬＬ效应法和电化学Ｃ－Ｖ分布研究其特性。讨论了ＩｎＧａＡｓ／ＧａＡｓ宜质结杨效应晶体管（ＨＦＥＴ）的优越性。和ＧａＡｓ ＭＥＳＦＥＴＳ或ＨＥＭＴ相比,由于ＨＦＥＴ没有Ａｌ组份,具有低温特性好,低噪声和高增益等特点。本文研究了具有ＩｎＧａＡｓ／ＧａＡｓ双沟道和独特掺杂分布的低噪声高增益ＨＦＥＴ。     

Annealing behavior of undoped bulk GaAs

Heat treatments of bulk undoped GaAs in a sealed ampoule (800° C, 0.5 or 1 h) and in a covered LPE boat under H₂ (695° C, 51 h) were performed with different surface conditions,i.e., exposed surface, proximate surface and a Ga(As) solution covered surface. Four characterization techniques, namely Polaron profile, secondary ion mass spectroscopy (SIMS), photoluminescence (PL) and deep level transient spectroscopy (DLTS), were used to detect the changes in impurities and defects in the surface region of the samples. The carrier concentration profiles, the accumulation of impurities (such as C, Si, Mn and Cu), the PL features and the PL profiles of Mn and Cu related emissions, as well as the trap profiles of EL6 and EL2 for the different surface conditions all demonstrate the important role of both impurities and native defects in surface degradation and the influence of native defects on impurity incorporation.