分子束外延CdTe（211）B／GaAs（211）B的特性研究

ＣｄＴｅ／ＧａＡｓ是ＨｇＣｄＴｅ分子束外延的重要替代衬底材料。用Ｘ双晶衍射和光致发光测试研究了分子束外延生长的ＣｄＴｅ（２１１）Ｂ／ｇＡｓ（２１１）Ｂ的晶体结构质量，表明外延膜昌体结构完整，具有很高的质量。用高分辨率的透射电镜研究其界面特性，观察到ＣｄＴｅ（２１１）Ｂ相对于ＧａＡｓ（２１１）Ｂ向着（１１１）方向倾斜一个小角度，界面的四面体键网发生扭曲，由于晶格失配，在界面存在很高的失配位错密度。     

HgCdTe分子束外延的初步研究

ＨｇＣｄＴｅ分子束外延的初步研究何先忠，陈世达，林立（华北光电技术研究所北京１０００１５）ＨｇＣｄＴｅ单晶薄膜材料是下一代红外焦平面器件的首选材料。本文作者报道了在（２１１）ＢＧａＡｓ衬底上成功地外延生长出高质量的ＨｇＣｄＴｅ外延膜。得到了组分为０．...     

Hg1—xCdxTe多层薄膜材料结构缺陷的透射电子显微镜测定

用透射电镜对Ｈｇ１－ｘＣｄＴｅ／ＣｄＴｅ和ＣｄＴｅ／ＧａＡｓ两种异质结的横截面进行了观测分析，对异质结附近的某些结构缺陷，如微孪晶的尺寸，几何形态、层错、界面失配位错的组态特征进行了研究，并对多层膜之间的取向差进行了分析，说明在ＧａＡｓ衬底上用分子束外延法制备的Ｈｇ１－ｘＣｄｘＴｅ／ＣｄＴｅ／ＧａＡｓ多层膜，就大量结构缺陷而言，ＣｄＴｅ缓冲层对Ｈｇ１－ｘＣｄｘＴｅ外延层起到了屏障作用，在Ｈｇ１－ｘ     

分子束外延HgCdTe薄膜位错密度的研究

本文报道在晶格失配ＧａＡｓ衬底上分子束外延ＨｇＣｄＴｅ薄膜的位错密度研究结果．用位错腐蚀坑密度（ＥＰＤ）、Ｘ射线双晶衍射以及透射电子显微镜方法,对ＣｄＴｅ缓冲层以及ＨｇＣｄＴｅ薄膜的位错密度、其纵向分布及与工艺条件的相关关系进行了评价、分析．研究发现退火可以有效地降低ＨｇＣｄＴｅ薄膜的位错密度．     

MBE生长的p－Hg_（1－x）Cd_xTe外延薄膜变磁场下的Hall系数及电导率

本文报道了利用分子束外延技术在ＧａＡｓ（２１１）Ｂ衬底上生长Ｈｇ１－ｘＣｄｘＴｅ／ＣｄＴｅ异质结，并通过ＶａｎｄｅｒＰａｕｗ（ＶｄＰ）方法测量Ｐ－Ｈｇ１－ｘＣｄｘＴｅ外延薄膜在不同温度及磁场下Ｈａｌｌ系数和电导率，采用最小二乘法对实验数据下行拟合，得到了混合导电机制下电子、重空穴和轻空穴的迁移率及载流子浓度．     

P型长波Hg_（1－x）Cd_xTe材料MBE生长技术研究

用分子束外延的方法在ＧａＡｓ（２１１）Ｂ衬底上研制了Ｐ型长波ＨｇＣｄＴｅ材料，及３２×３２小规模长波混成红外焦平面列阵，其材料的均匀性以及生长材料的参数的可重复性良好．在适当的热处理条件下，材料Ｐ型电学参数达到了较高水平，并具有良好的可重复性     

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．     

分子束外延碲镉汞薄中VODI缺陷的研究

ＨｇＣｄＴｅ薄膜中的Ｖｏｉｄ缺陷严重影响面阵器件的有效元数。对用分子束外延法在ＧａＡｓ衬底上生长的ＨｇＣｄＴｅ薄膜中的Ｖｏｉｄ缺陷进行了 形貌，剖面观测和能谱分析。     

利用CBE技术在Si衬底上生长GaAs薄膜

采用化学束外延（ＣＢＥ）技术，以三乙基镓（ＴＥＧ）和砷烷（ＡｓＨ３）为源，在Ｓｉ（００１）衬底上生长ＧａＡｓ薄膜．利用Ｈａｌｌ效应、卢瑟福背散射（ＲＢＳ）和高分辨率透射电子显微镜（ＨＲＴＥＭ）检测了外延层的质量．结果表明，ＧａＡｓ薄膜具有ｎ型导电性，载流子浓度为１．３×１０１５ｃｍ－３，其杂质估计是Ｓｉ，它来自衬底的自扩散．外延层的质量随着膜厚的增加而得到明显的改善．在ＧａＡｓ／Ｓｉ界面及其附近，存在高密度的结构缺陷，包括失配位错、堆垛层错和孪晶．这些缺陷完全缓解了ＧａＡｓ外延层和Ｓｉ衬底之间因晶格失配引     

GaAs上热壁外延Cd_（0．96）Zn_（0．04）Te薄膜

国内首次报道用热壁外延（ＨＷＥ）技术在（１００）ＧａＡｓ衬底上生长出Ｃｄ＿（０．９６）Ｚｎ＿（０．０４）Ｔｅ（１１１）薄膜。结果表明，薄膜在１５～２０μｍ厚时Ｘ射线双晶衍射回摆曲线半高宽在１００弧秒以下，其位错腐蚀坑密度等于甚至小于１０￣３ｃｍ￣（－２）薄膜组分、层厚均匀，表面光亮如镜，质量达到国际先进水平，优于国内Ｃｄ＿（０．９６）Ｚｎ＿（０．０４）Ｔｅ块晶，是外延生长ＨｇＣｄＴｅ的理想替代式衬底。文章强调了生长前ＧａＡｓ衬底，多晶源预处理的重要性。     

Correlation of CdZnTe(211)B substrate surface morphology and HgCdTe(211)B epilayer defects

We present results on the surface morphology and recombination lifetimes of molecular-beam epitaxy (MBE)-grown HgCdTe (211)B epilayers and correlate them with the roughness of the CdZnTe substrate surfaces. The substrate surface quality was monitored by in-situ spectroscopic ellipsometry (SE) and reflection high-energy electron diffraction (RHEED). The SE roughness of the substrate was measured after oxide desorption in the growth chamber. The RHEED patterns collected show a strong correlation with the SE roughness. This proves that SE is a valuable CdZnTe prescreening tool. We also found a correlation between the substrate roughness and the epilayer morphologies. They are characterized by a high density of thin elongated defects, “needle defects,” which appear on most samples regardless of growth conditions. The HgCdTe epilayers grown on these substrates were characterized by temperature-dependent, photoconductive decay-lifetime data. Fits to the data indicate the presence of mid-gap recombination centers, which were not removed by 250°C/24-h annealing under a Hg-rich atmosphere. These centers are believed to originate from bulk defects rather than Hg vacancies. We show that Te annealing and CdTe growth on the CdZnTe substrates smooth the surface and lower substantially the density of needle defects. Additionally, a variety of interfacial layers were also introduced to reduce the defect density and improve the overall quality of the epilayer, even in the presence of less than perfect substrates. Both the perfection of the substrate surface and that of its crystalline structure are essential for the growth of high-quality material. Thus, CdZnTe surface polishing procedures and growth techniques are crucial issues.     

High-Quality (211)B CdTe on (211)Si Substrates Using Metalorganic Vapor-Phase Epitaxy

High-quality (211)B CdTe buffer layers are required during Hg_1−x Cd _x Te heteroepitaxy on Si substrates. In this study, direct metalorganic vapor-phase epitaxy (MOVPE) of (211)B CdTe on Si, as well as CdTe on Si using intermediate Ge and ZnTe layers, has been achieved. Tertiary butyl arsine was used as a precursor to enable As surfactant action during CdTe MOVPE on Si. The grown CdTe/Si films display a best x-ray diffraction rocking-curve full-width at half-maximum of 64 arc-s and a best Everson etch pit density of 3 × 10⁵ cm⁻². These values are the best reported for MOVPE-grown (211)B CdTe/Si and match state-of-the-art material grown using molecular-beam epitaxy.     

Anisotropic Surface Roughness in Molecular-Beam Epitaxy CdTe (211)B/Ge(211)

We characterize the surface of molecular-beam epitaxy (MBE)-grown CdTe(211)B/Ge(211) by atomic-force microscopy (AFM), optical interference microscopy, and generalized ellipsometry (GE). We find that, for substrate temperatures above 300°C, the surface is rough and hazy; the AFM root-mean-square roughness is of the order of 150 Å. It appears from GE that the optical response is anisotropic, the principal axes of anisotropy being along the $ [\overline{1} 11] We characterize the surface of molecular-beam epitaxy (MBE)-grown CdTe(211)B/Ge(211) by atomic-force microscopy (AFM), optical interference microscopy, and generalized ellipsometry (GE). We find that, for substrate temperatures above 300°C, the surface is rough and hazy; the AFM root-mean-square roughness is of the order of 150 ?. It appears from GE that the optical response is anisotropic, the principal axes of anisotropy being along the and directions. For a substrate temperature of approximately 300°C, the surface is smooth and mirror-like and the AFM roughness is as low as 45 ?. The sample is still anisotropic, even though the magnitude of the cross-polarized reflection coefficients are very small in this case. It appears that the anisotropy originates from the surface roughness, not the bulk.     

In-situ ellipsometry studies of adsorption of Hg on CdTe(211)B/Si(211) and molecular beam epitaxy growth of HgCdTe(211)B

We study the adsorption of Hg on CdTe(211)B using an 88-wavelength spectroscopic ellipsometer mounted on a commercial, molecular beam epitaxy (MBE) chamber. A detailed analysis of the pseudo-dielectric function shows that Hg is present at the surface both in chemisorbed and physisorbed form. Effective medium models for a mixture of chemisorbed and physisorbed Hg on the microscopically rough CdTe surface could not fit our data. However, a proposed model in which a partial layer of physisorbed Hg sits on top of a partial layer of chemisorbed Hg fits the measured pseudo-dielectric function well and yields precise values for the thicknesses of the chemisorbed and the physisorbed Hg layers. These values change in the expected manner as a function of Hg flux, temperature, and Te coverage. An analysis of the uncertainty in the measured thicknesses is carried out in detail, and a study of the limitations of the ellipsometer used for this study is presented. The effects of these limitations on the precision and accuracy of in-situ data are enumerated.     

Lattice Relaxation and Dislocation Reduction in MBE CdTe(211)B/Ge(211)

We have used x-ray diffraction to assess the thickness dependence of strain in molecular-beam epitaxial (MBE) CdTe(211)/Ge(211). For 25-nm-thick layers, we find tensile stress of 100 MPa and in-plane strain of ~1.5 × 10⁻³. This stress relaxes during growth and becomes zero beyond 1 μm. We use the Dunn and Koch formula to estimate the threading dislocation density from the full-width at half-maximum of the (224) rocking curve. We then estimate the annihilation radius of MBE-grown CdTe(211)B/Ge(211) to be ~10 nm. Our layers have etch pit densities between 5 × 10⁷ cm⁻² and 5 × 10⁶ cm⁻² for a thickness of 10 μm. The lowest densities were obtained by periodic annealing epitaxy. We discuss mechanisms for the saturation of the dislocation density.     

Surface structure of plasma-etched (211)B HgCdTe

The surface of (211)B HgCdTe has been studied by reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM). RHEED analysis of the as-grown Hg-rich molecular beam epitaxy (MBE) (211)B HgCdTe suggests the surface reconstructs by additional Hg incorporation. The plasma-etched (211)B HgCdTe surface is crystalline but stepped and facetted. RHEED analysis indicates asymmetric pyramids (base dimensions ≈0.5×1.1 nm) are formed to minimize surface Hg concentration. The AFM examination of plasma-etched (211)B HgCdTe reveals oriented mesoscopic features.     

Helium-Plasma-Prepared (111)A HgCdTe and (211)B InSb

Brief low-energy helium plasma exposure of mercury cadmium telluride and indium antimonide results in oxide- and elemental-component-free, nearly stoichiometric surfaces. In these initial experiments, the only remaining residue is a topmost trace layer of carbon similar to that present on wet etched and reduced surfaces. The nature of these surfaces was determined by in situ Auger electron spectroscopy, monochromatic X-ray photoelectron, and ion scattering spectroscopy, and compared with established wet chemical and hydrogen argon plasma preparations.     

Cyclic Annealing During Metalorganic Vapor-Phase Epitaxial Growth of (211)B CdTe on (211) Si Substrates

High-quality (211)B CdTe buffer layers on Si substrates are required to enable Hg_1–x Cd _x Te growth and device fabrication on lattice-mismatched Si substrates. Metalorganic vapor-phase epitaxy (MOVPE) of (211)B CdTe on Si substrates using Ge and ZnTe interlayers has been achieved. Cyclic annealing has been used during growth of thick CdTe layers in order to improve crystal quality. The best (211)B CdTe/Si films grown in this study display a low x-ray diffraction (XRD) rocking-curve full-width at half-maximum (FWHM) of 85 arcsec and etch pit density (EPD) of 2 × 10⁶ cm⁻². These values are the best reported for MOVPE-grown (211) CdTe/Si and are comparable to those for state-of-the-art molecular beam epitaxy (MBE)-grown CdTe/Si.     

Metalorganic Vapor-Phase Epitaxial Growth of (211)B CdTe on (211) Si Using Ge Interfacial Layer

We have achieved metalorganic vapor-phase epitaxial growth of (211)B CdTe on Si without the requirement of a pregrowth high-temperature oxide desorption step. This was achieved by growing a thin Ge film on the starting (211) Si substrates. To get (211)B CdTe orientation, the Ge surface was exposed to As prior to the start of CdTe growth. A thin ZnTe interlayer between Ge and CdTe has been shown to improve the CdTe surface morphology.     

分子束外延用碲锌镉(211)B衬底表面预处理技术

本文主要分析了作为分子束外延碲镉汞的碲锌镉衬底的表面预处理工艺。湿化学处理工艺主要目的是去除衬底表面损伤层,0.5%溴甲醇溶液的腐蚀速率为7 nm/s,但腐蚀的同时会形成表面富Te层和氧化层,氧化层的厚度随溴甲醇的浓度增加而增加;高温热处理工艺主要是消除湿化学腐蚀形成的富Te层和氧化层,340℃的高温处理可去除表面氧化层;也可以直接通过回旋共振等离子体处理衬底表面,形成化学计量比正常的干净表面。