Progress in the Molecular Beam Epitaxy of HgCdTe on Large-Area Si and CdZnTe Substrates

This paper presents the progress in the molecular beam epitaxy (MBE) growth of HgCdTe on large-area Si and CdZnTe substrates at Raytheon Vision Systems. We report a very high-quality HgCdTe growth, for the first time, on an 8 cm × 8 cm CdZnTe substrate. This paper also describes the excellent HgCdTe growth repeatability on multiple 7 cm × 7 cm CdZnTe substrates. In order to study the percentage wafer area yield and its consistency from run to run, small lots of dual-band long-wave infrared/long-wave infrared triple-layer heterojunction (TLHJ) layers on 5 cm × 5 cm CdZnTe substrates and single-color double-layer heterojunction (DLHJ) layers on 6-inch Si substrates were grown and tested for cutoff wavelength uniformity and micro- and macrovoid defect density and uniformity. The results show that the entire lot of 12 DLHJ-HgCdTe layers on 6-inch Si wafers meet the testing criterion of cutoff wavelength within the range 4.76 ± 0.1 μm at 130 K and micro- and macrovoid defect density of ≤50 cm⁻² and 5 cm⁻², respectively. Likewise, five out of six dual-band TLHJ-HgCdTe layers on 5 cm × 5 cm CdZnTe substrates meet the testing criterion of cutoff wavelength within the range 6.3 ± 0.1 μm at 300 K and micro- and macrovoid defect density of ≤2000 cm⁻² and 500 cm⁻², respectively, on the entire wafer area. Overall we have found that scaling our HgCdTe MBE process to a 10-inch MBE system has provided significant benefits in terms of both wafer uniformity and quality.     

Characterization of HgCdTe Films Grown on Large-Area CdZnTe Substrates by Molecular Beam Epitaxy

Recent advances in growth of Hg_1?x Cd _x Te films on large-area (7 cm × 7.5 cm) CdZnTe (CZT) substrates is presented. Growth of Hg_1?x Cd _x Te with good uniformity on large-area wafers is achieved using a Riber 412 molecular beam epitaxy (MBE) tool designed for growth of Hg_1?x Cd _x Te compounds. The reactor is equipped with conventional CdTe, Te, and Hg sources for achieving uniform exposure of the wafer during growth. The composition of the Hg_1?x Cd _x Te compound is controlled in situ by employing a closed-loop spectral ellipsometry technique to achieve a cutoff wavelength (λ _co) of 14 μm at 78 K. We present data on the thickness and composition uniformity of films grown for large-format focal-plane array applications. The composition and thickness nonuniformity are determined to be <1% over the area of a 7 cm × 7.5 cm wafer. The films are further characterized by Fourier-transform infrared spectroscopy, optical microscopy, and Hall measurements. Additionally, defect maps show the spatial distribution of defects generated during the epitaxial growth of the Hg_1?x Cd _x Te films. Microdefect densities are in the low 10³ cm^?2 range, and void defects are below 500 cm^?2. Dislocation densities less than 5 × 10⁵ cm^?2 are routinely achieved for Hg_1?x Cd _x Te films grown on CZT substrates. HgCdTe 4k × 4k focal-plane arrays with 15 μm pitch for astronomical wide-area infrared imagers have been produced using the recently developed MBE growth process at Teledyne Imaging Sensors.     

Growth of GaN Layers on Si(111) Substrates by Plasma-Assisted Molecular Beam Epitaxy

Semiconductors - The studies of the growth kinetics of GaN layers grown on nitridated Si(111) substrates by plasmaassisted molecular beam epitaxy are presented. The nucleation and overgrowth of the...     

MBE Growth of HgCdTe on Large-Area Si and CdZnTe Wafers for SWIR,MWIR and LWIR Detection

Molecular beam epitaxy (MBE) growth of HgCdTe on large-size Si (211) and CdZnTe (211)B substrates is critical to meet the demands of extremely uniform and highly functional third-generation infrared (IR) focal-panel arrays (FPAs). We have described here the importance of wafer maps of HgCdTe thickness, composition, and the macrodefects across the wafer not only to qualify material properties against design specifications but also to diagnose and classify the MBE-growth-related issues on large-area wafers. The paper presents HgCdTe growth with exceptionally uniform composition and thickness and record low macrodefect density on large Si wafers up to 6-in in diameter for the detection of short-wave (SW), mid-wave (MW), and long-wave (LW) IR radiation. We have also proposed a cost-effective approach to use the growth of HgCdTe on low-cost Si substrates to isolate the growth- and substrate-related problems that one occasionally comes across with the CdZnTe substrates and tune the growth parameters such as growth rate, cutoff wavelength (λ _cutoff) and doping parameters before proceeding with the growth on costly large-area CdZnTe substrates. In this way, we demonstrated HgCdTe growth on large CdZnTe substrates of size 7 cm × 7 cm with excellent uniformity and low macrodefect density. Received December 7, 2007; accepted February 25, 2008     

HgCdTe Molecular Beam Epitaxy Growth Temperature Calibration Using Spectroscopic Ellipsometry

In this work, spectroscopic ellipsometry (SE) is demonstrated as a technique to calibrate growth temperature measurement devices (thermocouples and pyrometers) prior to real mercury cadmium telluride (HgCdTe) growth. A pyrometer is used to control the substrate temperature in molecular beam epitaxy (MBE) for the growth of HgCdTe-based material. It is known that a very narrow optimal growth temperature range exists for HgCdTe, typically ±5°C. A nonoptimal growth temperature will negatively impact on material quality by inducing growth defects, reducing composition uniformity, causing difficulty in controlling doping incorporation, promoting poor electronic properties, and having other adverse effects. Herein, we present a method for measuring and calibrating substrate temperature measurement equipment by using spectroscopic ellipsometry (SE) prior to real HgCdTe growth. This method is easy to implement, nondestructive, and reliable. The proposed method requires one substrate with a surface material with optical properties well known in the temperature range of interest, but not necessarily the same base material as the material to be grown. In the specific case of this work, we use epitaxial CdTe material on top of a Si substrate. This wafer was used to create a database of its optical properties as a function of temperature by using SE. From the collected optical parameters, a model is built and a fit is generated from the SE data collected. The temperature can then be determined by fitting the temperature-dependent SE measurements from this specific CdTe material. The angle offset and surface roughness parameters are also included in the model to account for changes in the average run-to-run angle variations and surface conditions over time. This work does not attempt to obtain an absolute temperature, but rather a reliable and repeatable relative temperature measurement.     

HgCdTe Research at FFI: Molecular Beam Epitaxy Growth and Characterization

This paper presents results from recent work on molecular beam epitaxy growth of HgCdTe at the Norwegian Defence Research Establishment (FFI), including studies of material properties and fabrication of photodiodes and nanostructures. Systematic studies of defect morphology in HgTe and Hg_1−x Cd _x Te have revealed that there is a minimum in the area covered by defects just below the onset of Te precipitation. The shape and density of microvoids in HgTe can be used to determine the deviation from the optimal growth temperature. This can be further related to the optimal growth temperature of Hg_1−x Cd _x Te with any Cd mole fraction by thermodynamic calculations. A mechanism for the formation of microvoids and needles has been presented. Photoluminescence (PL) has been used to study layers without doping and with Hg vacancy, Ag, and In doping. Planar photodiodes with high dynamic resistance and good quantum efficiency were fabricated by ion-milling vacancy-doped mid-wave and long-wave infrared layers. Quantum wells (QWs) with good crystallinity and high PL light output have been grown. Surface patterning has been found to enhance light emission from HgCdTe thin-film and QW samples by ∼30%. Single-crystal HgTe and segmented HgTe/Te nanowires have been grown, and the resistivity of the nanowires has been measured by conductive atomic force microscopy (AFM), where the AFM tip has been used as a mobile electrode.     

Influence of Substrate Orientation on the Growth of HgCdTe by Molecular Beam Epitaxy

An empirical study is reported, wherein HgCdTe was deposited simultaneously on multiple CdZnTe substrates of different orientations by molecular beam epitaxy. These orientations included the following vicinal surfaces: (115)B, (113)B, (112)B, and (552)B. Additionally, growth on (111)B was explored. Growth conditions found to be nearly optimalfor the standard (112)B orientation were selected. Through a series of growth runs, substrate temperature was varied, and the physical properties of the resulting HgCdTe epilayers were measured. These measurements included Nomarski microscopy, infrared transmission, x-ray diffraction, and defect decoration etching. The properties of HgCdTe epilayers as a function of temperature were roughly similar for all vicinal surfaces. Namely, as the temperature increased, the dislocation density decreased. At some critical temperature, the density of void defects increased dramatically. This critical temperature varied with orientation, the (115)B exhibiting the lowest critical temperature and the (112)B and (552)B exhibiting the highest. The (115)B, (113)B, and (112)B orientations exhibited “needlelike” defects on the as-grown HgCdTe surface. The density of these defects decreased with increasing temperature. The (552)B surface exhibited no such defects and growth behavior nearly identical to the (112)B growthsurface.     

CdZnTe Substrate Surface Preparation Technology at ASELSAN,Inc. for Molecular Beam Epitaxy Growth of High Quality HgCdTe Epilayers

High quality CdZnTe substrates with 4% ZnTe mole fraction are used for epitaxial growth of HgCdTe infrared detector layers. Molecular Beam Epitaxy (MBE) growth of HgCdTe epilayers requires high quality surface layer with sub-nanometer surface roughness values as well. We report on the development of a CdZnTe substrate surface preparation process for MBE growth of high quality HgCdTe epilayers. Surface preparation processes were performed on both commercially available CdZnTe substrates and substrates obtained from in-house grown CdZnTe boules. We developed a multi-step substrate surface processing flow to achieve sub-nanometer surface roughness, low total thickness variation (TTV), and wax or slurry residue free CdZnTe substrate surfaces. Each process step was optimized with the aim of removing the subsurface damage caused by the previous process step; so that we reduce the amount of damaged layer needed to be etched prior to epitaxy. Our developed surface preparation process can be applicable to commercially available CdZnTe substrates with high surface roughness and high TTV. This process was also optimized for as-cut CdZnTe slices. We are capable of processing typically 25 mm?×?25 mm CdZnTe substrates with achievable surface roughness values (R_rms) down to below 0.5 nm.     

InP基功率HEMT结构材料分子束外延生长研究

从 3个层面研究了分子束外延 Al0 .48In0 .52 As/ Ga0 .47In0 .53As/ In P功率 HEMT结构材料生长技术。首先 ,通过观察生长过程的高能电子衍射 (RHEED)图谱 ,确立了 Ga0 .47In0 .53As/ In P结构表面层的 MBE RHEED衍射工艺相图 ,据此生长的单层 Si-doped Ga0 .47In0 .53As(40 0 nm) / In P室温迁移率可达 6960 cm2 / V· s及电子浓度 1 .3 3 E1 7cm- 3。其次 ,经过优化结构参数 ,低噪声 Al0 .48In0 .52 As/ Ga0 .47In0 .53As/ In P HEMT结构材料的 Hall参数达到μ30 0 K≥ 1 0 0 0 0 cm2 / V· s、2 DEG≥ 2 .5 E1 2 cm- 2 。最后 ,在此基础之上 ,降低 spacer的厚度、在 Ga0 .47In0 .53As沟道内插入 Si平面掺杂层并增加势垒层的掺杂浓度获得了功率 Al0 .48In0 .52 As/ Ga0 .47In0 .53As/ In PHEMT结构材料 ,其 Hall参数达到μ30 0 K≥ 80 0 0 cm2 / V· s、2 DEG≥ 4 .0 E1 2 cm- 2 。     

低缺陷Si基碲镉汞分子束外延工艺研究

随着焦平面探测器向超大面阵、小像元方向发展,对盲元率尤其连续盲元、均匀性等要求越来越高。材料表面缺陷已经成为抑制Si基碲镉汞分子束外延(Molecular Beam Epitaxial, MBE)技术在更广范围内应用的一个重要因素。通过解决MBE系统束流稳定性、束流测量的精确性和生长温度控制的稳定性共3个MBE生长碲镉汞材料精确控制的关键问题,以及通过正交试验优化生长参数,将Si基碲镉汞材料缺陷密度控制在500 cm^-2以内,最优值达到57.83 cm^-2。     

Microstructure of Heteroepitaxial ZnTe Grown by Molecular Beam Epitaxy on Si(211) Substrates

The interface of ZnTe/Si(211) grown by molecular beam epitaxy was investigated by high-resolution transmission electron microscopy. Several types of defects such as misfit dislocations, stacking faults, agglomerations of vacancies, and precipitates were observed and studied by electron microscopy at the ZnTe/Si interface. The distribution of misfit dislocations at the interface was revealed with the assistance of the fast Fourier transformation filtering technique. A stick-and-ball interface model including misfit dislocation geometry is proposed. The possible origins of the stacking faults, vacancies, and precipitates are discussed.     

HgCdTe外延用的CdZnTe衬底研制

阐述了ＣｄＺｎＴｅ衬底在红外焦平面阵列探测器研究中的重要性;概括了ＣｄＺｎＴｅ晶体生长的方法、原理和工艺步骤;分析了影响晶体质量（单晶面积、组分及均匀性、结晶完整性、光电特性）的因素,并提出了与质量相关的控制技术;介绍了ＣｄＺｎＴｅ衬底制备过程中,晶片处理的工艺和步骤（晶锭的定向切割、单晶划片、极性鉴别、磨抛、腐蚀）;报道了目前ＣｄＺｎＴｅ晶体的性能水平,晶片处理结果和ＣｄＺｎＴｅ的应用情况。     

分子束外延In掺杂硅基碲镉汞研究

利用分子束外延(Molecular Beam Epitaxy, MBE)系统生长了In掺杂硅基碲镉汞(Mercury Cadmium Telluride, MCT)材料。通过控制In源温度获得了不同掺杂水平的高质量MCT外延片。二次离子质谱仪(Secondary Ion Mass Spectrometer, SIMS)测试结果表明,In掺杂浓度在1×10¹⁵～2×10¹⁶ cm^-3之间。表征了不同In掺杂浓度对MCT外延层位错的影响。发现位错腐蚀坑形态以三角形为主(沿<■>方向排列),且位错密度与未掺杂样品基本相当。对不同In掺杂浓度的材料进行汞饱和低温处理后,样品的电学性能均有所改善。结果表明,In掺杂能够提高材料的均匀性,从而获得较高的电子迁移率。     

Impact of CdZnTe Substrates on MBE HgCdTe Deposition

The highest sensitivity, lowest dark current infrared focal plane arrays (IRFPAs) are produced using HgCdTe on CdZnTe substrates. As-received state-of-the-art CdZnTe 6 × 6 and 7 × 7.5 cm substrates were analyzed using Nomarski phase contrast microscopy, Auger electron spectroscopy, scanning electron microscopy/energy dispersive spectroscopy, and scanning profilometry. On all CdZnTe substrates tested, we observed as-received large area macro-defect contamination. Using a defect specification limit of 50 contiguous defective pixels, we identified non-compliant 1280 × 720 12-μm pitch focal plane arrays due to as-received substrate macro-defect contamination. Using the above specification, up to 20% IRFPA wafer yield loss is due to state-of-the-art as-received CdZnTe substrate macro-contamination.     

Influences of Te-Rich and Cd-Rich Precipitates of CdZnTe Substrates on the Surface Defects of HgCdTe Liquid-Phase Epitaxy Materials

Influences of Te-rich and Cd-rich precipitates of CdZnTe substrates on the surface defects of HgCdTe epilayers grown by Te-rich liquid-phase epitaxy were investigated. The results show that HgCdTe surface defects are mainly attributable to precipitates on CdZnTe substrate surfaces. At the same time, the remelting of substrate surface layers during the liquid-phase epitaxial process also affects the number and morphology of HgCdTe surface defects. According to the morphological characteristics of surface defects, three types of surface defects were observed on the surfaces of HgCdTe epilayers. There are no obvious differences in the morphologies of the surface defects grown on Te-rich and Cd-rich substrates. However, the dislocation distributions around surface defects are different for HgCdTe epilayers grown on different substrates.     

用气态源分子束外延生长法制备Si/SiGe/Sinpn异质结双极晶体管

用气态源分子束外延法制备了Ｓｉ／ＳｉＧｅ／Ｓｉｎｐｎ异质结双极晶体管．晶体管基区Ｇｅ组分为０．１２,Ｂ掺杂浓度为１．５e１９ｃｍ－３,ＳｉＧｅ合金厚度约４５ｎｍ．直流特性测试表明,共发射极直流放大倍数约５０,击穿电压ＶＣＥ约９Ｖ;射频特性测试结果表明,晶体管的截止频率为７ＧＨｚ,最高振荡频率为２．５ＧＨｚ．     

用气态源分子束外延生长法制备Si/SiGe/Si nPn异质结双极晶体管

用气态源分子束外延法制备了Si/SiGe/Si npn异质结双极晶体管.晶体管基区Ge组分为0.12,B掺杂浓度为1.5×101 9cm-3, SiGe合金厚度约45nm.直流特性测试表明,共发射极直流放大倍数约50,击穿电压VCE约9V;射频特性测试结果表明,晶体管的截止频率为7GHz,最高振荡频率为2.5GHz.     

Surface Structure of Molecular Beam Epitaxy (211)B HgCdTe

The as-grown molecular beam epitaxy (MBE) (211)B HgCdTe surface has variable surface topography, which is primarily dependent on substrate temperature and substrate/epilayer mismatch. Nano-ripple formation and cross-hatch patterning are the predominant structural features observed. Nano-ripples preferentially form parallel to the \( [\bar {1}11] \) and are from 0 Å to 100 Å in height with a wavelength between 0.1 μm and 0.8 μm. Cross-hatch patterns result from slip dislocations in the three {111} planes intersecting the (211) growth surface. The cross-hatch step height is 4 ± 1 Å (limited data set). This indicates that only a bi-layer slip (Hg/Cd + Te) in the {111} slip plane occurs. For the deposition of MBE (211)B HgCdTe/CdTe/Si, the reorientation of multiple nano-ripples coalesced into “packets” forms cross-hatch patterns. The as-grown MBE (211)B CdTe/Si surface is highly variable but displays nano-ripples and no cross-hatch pattern. Three types of defects were observed by atomic force microscopy (AFM): needle, void/hillock, and voids.     

Terahertz Emission from GaAs Films on Si(100) and Si(111) Substrates Grown by Molecular Beam Epitaxy

We report on the terahertz emission from femtosecond-laser-irradiated GaAs layers grown on Si(100) and Si(111) substrates. The results show that the terahertz emission from GaAs on Si is stronger than that of a semi-insulating bulk GaAs crystal. This increase is attributed to the strain field at the GaAs/Si interface. In the GaAs of the Si(100) sample, the stronger terahertz emission is observed compared with GaAs on Si(111). Moreover, the effect of changing the doping type of the Si substrate from n-type to semi-insulating was also studied and it was found that the terahertz emission intensity of GaAs on semi-insulating Si(100) is stronger than that of GaAs on n-type Si(100). Finally, strong terahertz emission from GaAs on semi-insulating Si(100) was observed not only in the reflection geometry but also in the transmission geometry. These results hold promise for new applications of terahertz optoelectronics.