Sacrificial etching of Al<Subscript>x</Subscript>Ga<Subscript>1-x</Subscript>As for III–V MEMS surface micromachining

A study of Al_xGa_1-xAs as a sacrificial film for surface micromachining is presented. Al_xGa_1-xAs etch rate and selectivity are measured over a range of aluminum mole fractions and HF etchant concentrations during the release of structural features up to 500 μm in width. The etch process is found to be diffusion limited, with an inverse power law relationship between etch depth and etch rate. Excellent selectivity greater than 10⁵ is achieved between sacrificial AlAs and structural GaAs, even for long etches up to 250 μm in length. Compared with previous studies of Al_xGa_1-xAs etching for epitaxial liftoff processing, measured etch rates for surface micromachining are approximately an order of magnitude lower, primarily due to the longer effective etch lengths required. However, unlike epitaxial liftoff, Al_xGa_1-xAs surface micromachining is compatible with higher HF concentrations which can provide comparable overall etch rates, with important implications for AlGaAs MEMS fabrication. PACS 81.05.Ea; 85.85.+j     

Preparation and study of p-n junction structures based on solid solutions AlxGa1-xSb

Layers of the solid solutions Al_xGa_1-xSb and p-n junctions based on these materials are prepared on gallium antimonide substrates by liquid epitaxy methods. Electrical characteristics of structures with AlSb content in the junction region up to 57 mol. % are evaluated. It is shown that reverse current in such structures decreases with increase in AlSb content. Photosensitivity spectra for p-n junctions with various Al_xGa_1-xSb compositions are presented.     

用肖特基电容电压特性数值模拟法确定调制掺杂AlxGa1-xN/GaN异质结中的极化电荷

研究发展了用肖特基电容电压特性数值模拟确定调制掺杂Al_xGa_1-xN/GaN异质结中极化电荷的方法.在调制掺杂的Al_0.22Ga_0.78N/GaN异质结上制备了Pt肖特基接触,并对其进行了C-V测量.采用三维费米模型对调制掺杂的Al_0.22Ga_0.78N/GaN异质结上肖特基接触的C-V特性进行了数值模拟,分析了改变样品参数对C-V特性的影响.利用改变极化电荷、n-AlGaN 关键词： xGa_1-xN/GaN异质结')" href="#">Al_xGa_1-xN/GaN异质结 极化电荷 电容电压特性 数值模拟     

Hot electron energy and momentum relaxation in GaAs/AlAs and GaAs/Ga1-xAlxAs multiple quantum wells

Experimental results on high electric field longitudinal transport in GaAs/AlAs and GaAs/Ga_1-xAl_xAs multiple quantum wells (MQW) are presented and compared with the prediction of a dielectric continuum model. We draw from our experiments the following four conclusions.(i) In GaAs/Ga_1-xAl_xAs systems the dominant energy and momentum relaxation mechanism is through scattering with GaAs -modes.(ii) However, in GaAs/AlAs systems the AlAs interface mode is dominant in relaxing the energy and momentum of the quantum well electrons.(iii) The hot electron momentum relaxation as obtained from the high-field drift velocity experiments is strongly affected by the production of hot phonons as expected from a model involving a non-drifting hot phonon distribution.(iv) The importance of the AlAs interface mode in GaAs/Ga_1-xAl_xAs MQW is not the result of the intrinsic scattering rate but related to its shorter lifetime, compared to GaAs modes.     

高组份Al值的AlxGa1-x As和AlxGa1-x As/GaAs/AlxGa1-xAs/GaAs多层结构的MOCVD生长

用自制常压MOCVD系统,在半绝缘GaAs衬底上生长高Al组份Al_xGa_1-xAs（其x值达0.83）,和Al_xGa_1-xAs/GaAs/Al_xGa_1-xAs/GaAs多层结构,表面镜面光亮。生长层厚度从几十到十几μm可控,测试表明外延层晶格结构完整,x值调节范围宽,非有意掺杂低,高纯GaAs外延层载流子浓度n_300K=1.7×10¹⁵cm^-3,n_77K=1.4×10¹⁵cm^-3,迁移率μ_300K=5900cmcm²/V.S,μ_77K=55500cm²/V.S。用电子探针,俄歇能谱仪测不出非有意掺杂的杂质,各层间界面清晰平直。 对GaAs,AlGaAs生长层表面缺陷,衬底偏角生长温度及其它生长条件也进行了初步探讨。     

Photoluminescence and persistent photoconductivity of Al<Subscript>x</Subscript>Ga<Subscript>1-x</Subscript>N/GaN heterostructures

We have investigated the optical properties of Al_xGa_1-xN/GaN heterostructures (x=0.08, 0.15, 0.33) grown by metal organic chemical vapor deposition on sapphire using photoluminescence (PL) and persistent photoconductivity (PPC) measurements. For the Al_xGa_1-xN/GaN heterostructures (HS) containing high Al composition, we observed an anomalous temperature-dependent photoluminescence and persistent photoconductivity effects. These results show a strong dependence of the physical properties of Al_xGa_1-xN/GaN HS on the Al content and layer thickness. The anomalous temperature-dependent PL is usually attributed to the presence of carrier localization states. These phenomena are explained based on the alloy compositional fluctuations in the Al_xGa_1-xN/GaN HS. From the PPC measurements, the photocurrent (PC) quenching was observed for Al_xGa_1-xN/GaN HS and it is explained by the metastable states formed in the underlying GaN layer. Also, the mechanisms behind the PC quenching and PPC phenomena are explained in detail. PACS 72.20.Jv; 72.40.+w; 78.55.Cr     

Light scattering in GaAs parabolic quantum wells

We report the observation of electronic light scattering in photoexcited parabolic GaAsAl_xGa_1-xAs quantum wells. The spectra show sharp peaks corresponding to transitions between sublevels in the conduction band. The precision of the measurements allows a test of the simple harmonic oscillator model for the energy level structure. The energy gap and alloy composition of the Al_xGa_1-xAs layers are determined from resonance Raman scattering by optical phonons. We use these results to calculate the conduction band offset Q_e. We obtain Q_e ∼ 0.7, in agreement with recent experiments in square quantum wells.     

Si(111)衬底上生长有多缓冲层的六方GaN晶格常数计算和应变分析

利用卢瑟福背散射/沟道技术和高分辨率X射线衍射技术对在Si(111)衬底上利用金属有机化合物气相外延技术(MOVPE)生长有多缓冲层的六方GaN外延膜进行结晶品质计算、晶格常数计算和应变分析. 实验结果表明：GaN外延膜的结晶品质为χ_min=1.54%，已达到完美晶体的结晶品质(χ_min=1%—2%)；GaN外延膜的水平方向和垂直方向晶格常数分别为：a_epi＝0.31903nm，c_epi=0.51837nm，基本达到G 关键词： GaN 高分辨X射线衍射 卢瑟福背散射/沟道 弹性应变     

Tight-binding studies of the electronic band structure of GaAlN and GaInN alloys

The semi-empirical tight-binding (TB) approach with an sp³s^* orbital basis is used to investigate the electronic band structure of cubic Ga_1-xAl_xN and Ga_1-xIn_xN alloys. The spin–orbit splitting in the Hamiltonian and first- and second-neighbour interactions are considered to explore the gap evolution as a function of the concentration x. The TB parameters used in the studies were obtained within the virtual crystal approximation using those of the binary compounds AlN, GaN, and InN. The binary parameters are calculated by applying an empirical TB Hamiltonian taking into account first- and second-neighbour interactions. A direct to indirect gap transition is obtained for Ga_1-xAl_xN at x=0.60. In contrast, the Ga_1-xIn_xN alloys exhibit direct-gap characteristics as a consequence of being formed by the direct-gap binary compounds GaN and InN. PACS 71.20.Nr; 71.23.-k; 71.55.Eq     

Effect of oxidation on the optical and surface properties of AlGaN

The chemical properties of Al_xGa_1−xN surfaces exposed to air for different time periods are investigated by atomic force microscopy (AFM), photoluminescence (PL) measurement and X-ray photoelectron spectroscopy (XPS). PL and AFM results show that Al_xGa_1−xN samples exhibit different surface characteristics for different air-exposure times and Al contents. The XPS spectra of the Al 2p and Ga 2p core levels indicate that the peaks shifted slightly, from an AlN to an AlO bond and from a GaN to a GaO bond. All of these results show that the epilayer surface contains a large amount of Ga and Al oxides.     

GaAlAs低温液相外延研究

本文概述了GaAlAs低温液相外延技术在制作超薄外延层,包括量子阶材料中的工作;报道了在700℃和600℃下用液相外延技术生长的GaAlAs层厚度与生长时间的关系,以及在600℃下Ga_1-xAl_xAs外延层中工值与液相中Al含量的关系的实验结果;并且用扫描电镜测得在600℃下10s时间生长的Ga_0.9Al_0.1As层厚为30nm.     

Hydrogen sulphide doping of GaAs and AlxGa1−xAs grown by molecular beam epitaxy (MBE)

H₂S gas has been used during molecular beam epitaxy (MBE) growth of GaAs and Al _x Ga_1–x As as sulphur vector forn-type doping. Doping efficiencies are less than 10^–3 at usual growth temperatures, and are limited by an incorporation competitive surface process, probably 2Ga+H₂SGa₂S+H₂. In Al_xGa_1–x As forx0.2 the doping efficiency is further reduced by carrier freeze-out at deep levels. Measured thermal activation energies depend on growth conditions and remain relatively low even up to the direct-indirect bandgap crossover for substrate temperatures in the 585–645 C range.     

Gd3Al2-xGax合金的磁熵研究

用磁控电弧炉在氩气气氛中熔炼了Gd₃Al_2-xGax(x=0,0.1,0.3,0.5)系列合金.通过X射线粉末衍射和振动样品磁强计研究了样品的结构和磁熵.发现样品都是由Zr₃Al₂相组成的,且GdAlGa系列合金的ΔS_m要比Gd₃Al₂的大,峰值在室温附近,温区较宽,是一种较好的磁致冷材料. 关键词：     

Effects of a cap layer on built-in electric fields of AlxGa1-xN/GaN heterostructures non-destructively probed by Franz-Keldysh oscillations

We have investigated electric field strengths in the Al_xGa_1-xN layer, F_AlGaN's, of Al_xGa_1-xN/GaN heterostructures with and without a GaN cap layer using photoreflectance (PR) spectroscopy. Franz-Keldysh oscillations (FKOs) from the Al_xGa_1-xN layer are clearly observed in the PR spectra. It is found from analysis of the FKOs that stacking of the cap layer causes a remarkable enhancement of F_AlGaN. This fact demonstrates that the FKO profile is a non-destructive probe for a change of built-in electric field strength induced by a cap layer. Numerical calculations of F_AlGaN based on a Schr?dinger-Poisson equation clarify that the magnitude of the enhancement of F_AlGaN is dominated by the cap-layer thickness.     

稳定自然对流下的温度梯度液相外延

介绍了稳定自然对流下的温度梯度液相外延,稳定自然对流由加在溶液上的水平温差产生,用简化模式计算了该生长的生长速率,计算给出:该生长的生长速率与水平温差的平方根成比例;具体对Ga_0.85Al_0.15AS生长,在本工作给定的条件下,生长速率为稳态扩散理论预示生长速率的1124倍,在大部份生长面积内,外延层的厚度变化小于平均厚度的±10％,设计了稳定自然对流下的温度梯度液相外延装置,用该装置生长了厚Ga_1-xAl_xAs层,实 关键词：     

Strain-confined wires and dots at a GaAs/AlxGa1-xAs interface

We have observed lateral exciton confinement at the GaAs/Al_xGa_1-xAs interface. The confinement is achieved in both the growth and lateral directions by the strain potential under an amorphous carbon stressor. The potential welt varies from 15 meV to 40 meV for different stressor sizes. We have also made transient measurements on this structure, which show efficient exciton transfer from the bulk GaAs to the confined region.     

Maskless photoassisted etching of N-type Ga0.47In0.53As in basic solutions

The maskless photoassisted etching of n-type Ga_0.47In_0.53As is examined for basic KOH solutions in comparison with GaAs and InP material. The etch rate increases with laser intensity and with carrier concentration up to a saturation value. The best etch rate is obtained with molar KOH in ethyl alcohol (7 ms^–1 for laser intensity 10⁴ W cm^–2). Selective etching have been realized on heterojunction in order to isolate p-n junctions without the help of masks.     

热应力作用降低LPE层中的位错

提出由温差造成热剪切应力,引起衬底穿线位错滑移,形成<110>界面位错,从而降低LPE层中位错的模型。稳定自然对流下的温度梯度液相外延,存在衬底厚度方向的温差,能在边缘固定的衬底中造成热剪切应力。生长了厚GaAs和Ga_1-xAl_xAs层(x<0.3),估算的热剪切应力大于产生<110>暗线缺陷的临界剪切应力。表面腐蚀坑观察表明,外延层位错密度下降,或无位错。界面蚀槽和阴极荧光观察表明,衬底穿线位错在界面弯曲成<110>界面位错。透射电子显微镜观察表明,界面位错多 关键词：     

X-ray diagnostics of semiconductor heterostructures: Some achievements and perspectives for development

Possibilities of new approaches for the interpretation of X-ray scattering data to characterize heterostructures with nanosized layers are demonstrated. These approaches are based on both simultaneous mathematical analysis of the experimental data of X-ray rocking curves from several crystallographic planes of the sample and joint processing of the experimental data of X-ray diffraction and reflectometry. Measurements are taken using the same device with the advanced technique of experiments. In the approaches proposed, the volume of the experimental information on one sought parameter increases significantly, which provides a greater reliability of reconstructing the structural parameters of the object under study. A mathematical apparatus is developed along with the software to solve the inverse problem with a large amount of input data and sought parameters. The proposed approaches are tested on nanosized Al_xGa_1-xAs/In_yGa_1-yAs and In_xAl_1-xAs/In_yGa_1-yAs heterostructures grown on GaAs and InP substrates, respectively. It is shown that the complex X-ray method allows a reliable determination of relationships between the real structure and electrophysical properties, and thus an improvement of the technology for producing these objects with predicted properties.     

AlxGa1-xAs俄歇灵敏度因子的测定

利用PHI610俄歇谱仪测定了Al,Ga和As的俄歇灵敏度因子。对6种不同x值的Al_xGa_1-xAs样品进行俄歇定量分析。结果与X射线双晶衍射测量值非常一致。结果表明,利用自身谱仪测定的俄歇灵敏度因子进行的定量分析结果,与目前通常使用的手册或内标法提供的元素相对灵敏度因子的定量分析结果相比,测量精度得到大大提高。 关键词：