未掺杂CdZnTe与掺铟CdZnTe晶体的热处理

对于未掺杂Cd0.9Zn0.1Te晶片,采用在Cd/Zn气氛下,以In作为气相掺杂源进行热处理;而对于低阻In-Cd0.9Zn0.1Te晶片,则采用在Te气氛下进行热处理.分别研究了不同的热处理条件,包括温度、时间、pIn或pTe等对晶片电学性能、红外透过率以及Te夹杂/沉淀相的影响.结果表明,在Cd/Zn气氛下适当的掺In热处理和在Te气氛下适当的热处理均有效地提高了晶片的电阻率,分别达到2.3×1010和5.7×109Ω·cm,同时晶片的其他性能也得到明显改善.     

未掺杂CdZnTe与掺铟CdZnTe晶体的热处理

对于未掺杂Cd0.9Zn0.1Te晶片,采用在Cd/Zn气氛下,以In作为气相掺杂源进行热处理;而对于低阻In-Cd0.9Zn0.1Te晶片,则采用在Te气氛下进行热处理.分别研究了不同的热处理条件,包括温度、时间、pIn或pTe等对晶片电学性能、红外透过率以及Te夹杂/沉淀相的影响.结果表明,在Cd/Zn气氛下适当的掺In热处理和在Te气氛下适当的热处理均有效地提高了晶片的电阻率,分别达到2.3×1010和5.7×109Ω·cm,同时晶片的其他性能也得到明显改善.     

CdZnTe材料的表面钝化新工艺

研究了一种新的钝化CdZnTe(CZT)器件表面的工艺,即先采用KOH-KCl溶液对CZT表面进行处理,再用NH4F/H2O2溶液对其进行表面氧化的二步法钝化工艺.并借助俄歇电子能谱(AES)、微电流测试仪等手段对其表面钝化层的质量进行了鉴别,同时与KOH-KCl和NH4F/H2O2两种工艺进行了比较.AES能谱分析表明,采用二步法工艺钝化,既可获得化学计量比较好的CZT表面,又可在表面形成一层起保护作用的氧化层.I-Ⅴ特性曲线显示,两步法钝化后CZT器件的漏电流与KOH-KCl和NH4F/H2O2钝化相比都有一定程度的下降.说明文中提出的新工艺在CZT器件制备方面具有良好的应用前景.     

CdZnTe材料的表面钝化新工艺

研究了一种新的钝化CdZnTe(CZT)器件表面的工艺,即先采用KOHKCl溶液对CZT表面进行处理,再用NH4F/H2O2溶液对其进行表面氧化的二步法钝化工艺．并借助俄歇电子能谱（AES）、微电流测试仪等手段对其表面钝化层的质量进行了鉴别,同时与KOH KCl和NH4F/H2O2两种工艺进行了比较．AES能谱分析表明,采用二步法工艺钝化,既可获得化学计量比较好的CZT表面,又可在表面形成一层起保护作用的氧化层．I-V特性曲线显示,两步法钝化后CZT器件的漏电流与KOH KCl和NH4F/H2O2钝化相比都有一定程度的下降．说明文中提出的新工艺在CZT器件制备方面具有良好的应用前景．     

光诱导化学汽相淀积（LCVD）技术的研究进展

光诱导化学汽相淀(?)(LCVD)技术是一种新的低温化薄膜制备技术.本文首先评述了LCVD技术的特点、原理和装置,然后着重讨论了利用这种技术制备金属、半导体与化合物和介质薄膜以及一些淀积规律,最后指出了LCVD技术尚待解决的若干问题.     

CdZnTe晶片的红外透过率研究

测试了多个性能各异的Cd0.9Zn0.1Te晶片的红外透过率。研究表明,红外透过率与晶片的性能有着密切的联系,即红外透过率的大小及红外透过率图谱的形状可反映晶片的成分分布、位错密度以及杂质含量的情况。从晶片对红外光的吸收机理出发,对这些联系进行了详细的分析。     

Effect of constrained growth on defect structures in microgravity grown CdZnTe boules

In a microgravity environment obtainable in an orbiting space shuttle, it is possible to virtually eliminate gravity related effects such as buoyancy driven convection and hydrostatic forces thus providing an ideal environment for diffusion-controlled, containerless crystal growth processes. Under such conditions, it is possible to investigate the effects of gravity independent growth parameters on crystal growth. Studies of CdZnTe boules grown on space shuttle mission USML-1 revealed that regions of the boules grown with wall contact were associated with a higher defect density than regions grown with partial or no wall contact. Defect densities in certain regions grown without wall contact were as low as 5 × 10²/cm² to 1.2 × 10³/cm². More detailed studies on the effects of wall contact were sought in the USML-2 mission. Two CdZnTe boules (GCRC-1 and GCRC-2) were grown by the seeded Bridgman-Stockbarger method. Boule GCRC-1 was grown under constrained conditions to force full wall contact while boule GCRC-2 had a tapered geometry designed to minimize wall contact. Defect distributions in the boules were investigated by synchrotron white beam x-ray topography. The sample GCRC-1 was characterized by the presence of large inhomogeneous strains, numerous grains and twins, all of which are caused by effects related to wall contact. On the other hand, a part of the boule GCRC-2 that grew free from wall contact revealed minimum surface strains, the absence of twins and a very high structural uniformity. Results clearly verify that ampoule wall contact plays an important role in determining the incidence of crystal imperfections.     

Metalorganic vapor phase epitaxy of (100) CdZnTe layers using diisopropylzinc source

Growth characteristics of (100) Cd_1−xZn_xTe (CZT) have been studied using metalorganic vapor phase epitaxy. CZT layers were grown on (100) GaAs substrates using diisopropylzinc (DiPZn), dimethylcadmiun (DMCd), and diethyltelluride (DETe) as precursors. Growths were carried out in the temperature range from 375 to 450°C. Since DiPZn has lower vapor pressure than DMCd, CZT layers with Zn composition below 0.06 were grown with good compositional control. Layers with uniform Zn composition and thickness over an area of 10 × 15 mm² were grown. Enhancement of CZT growth rate was observed when a small amount of DiPZn is introduced under fixed flows of DMCd and DETe. Zn composition increases abruptly for further increase of DiPZn flow rate, where growth rate decreases. Growth mechanisms for the above growth conditions were also discussed.     

Growth characteristics of CdZnTe layers grown by metalorganic vapor phase epitaxy using dimethylzinc, dimethylcadmium, diethyltelluride, and dimethyltelluride as precursors

Growth characteristics of (100)-oriented CdZnTe layers grown by atmospheric-pressure metalorganic vapor phase epitaxy have been studied using dimethylzinc (DMZn), dimethylcadmium (DMCd), diethyltelluride (DETe), and dimethyltelluride (DMTe) as precursors. Variations of Zn composition and layer growth rate were examined by changing the DMZn supply ratio, defined as DMZn/(DMCd+DMZn), where the precursors are expressed in appropriate units of flow rate, from 0 (no DMZn) to 1.0 (no DMCd), while keeping the total group II supply rate constant. The growth rate of CdZnTe layers was found to decrease monotonically with increase of the DMZn supply ratio. On the other hand, the Zn composition x of grown layers increased gradually up to x=0.04 with increase of the DMZn supply ratio from 0 to 0.8, beyond which the Zn composition increased abruptly to ZnTe. The abrupt transition of Zn composition was suppressed by increasing the VI/II ratio. The growth mechanism of CdZnTe layers was studied based on the observed growth characteristics of CdTe and ZnTe. A higher desorption rate from the growth surface for Zn species than for Cd species, and a higher rate of CdTe formation than ZnTe formation are believed to cause the observed growth characteristics. CdZnTe layers with high crystal quality were grown in a wide range of Zn compositions. The full-width at half-maximum values for x-ray double-crystal rocking-curve measurements were lower than 320 arc-sec for x<0.3 and x>0.75.     

碲锌镉籽晶定向熔接技术研究

应用CdZnTe晶体作为衬底材料时,其晶向非常关键。CdZnTe晶体籽晶引晶定向生长技术能够有效提高晶体利用率。但是,受碲锌镉晶体生长方法限制,CdZnTe籽晶引晶技术成功率并不高。本文即通过一系列实验研究了籽晶熔接过程升温方式以及籽晶晶向对碲锌镉籽晶熔接成功率的影响,并确定了升温方式是籽晶熔接的关键工艺所在。后续籽晶引晶生长晶向能否持续与籽晶选择晶向有关。通过显著提升初始熔体过热度可以促进<111>籽晶引晶晶向的保持。     

Development of inclusion-free CdZnTe substrates from crystals grown by the vertical-gradient freeze method

With the aim of fabrication of (111) and (211) CdZnTe inclusion-free substrates for molecular-beam epitaxy (MBE) and liquid-phase epitaxy (LPE) growth of mercury cadmium telluride (MCT), we focused on fundamental research of the process of crystallization and cooling to room temperature. Based on the study of inclusion formation in dependence of Cd overpressure above the melt, an optimized process of crystal solidification was established. A key result of this study is the position of the Cd pressure, where inclusion-free crystals were fabricated without post-growth annealing. The crystals with a diameter of 100 mm and a height 40–50 mm were fabricated by the vertical-gradient freeze method (VGFM). The resulting ingots exhibit very good crystallographic quality, with a single-crystalline part filling 60–80% of the crystal volume. Substrates with orientation (111) and (211) and dimensions up to 4 × 4 cm were fabricated.     

A new growth method for CdTe: A breakthrough toward large areas

CdTe and CdZnTe are well-investigated II-VI semiconductors, mainly used as substrates for the HgCdTe-IR detection and as detectors for x-ray and γ-ray detection. For both applications, the demand is toward larger and larger dimensions to make larger infrared (IR) and x-ray and γ-ray arrays. This paper presents a new method to grow large dimension CdTe (or CdZnTe), mainly devoted to x-ray and γ-ray detection. This method is based on solvent evaporation from Te-rich solution made of cadmium and tellurium (optionally zinc); it operates in an open tube, and growth proceeds in a crucible maintained at a constant temperature. At the end of growth, a disc of CdTe (or CdZnTe) is obtained, the thickness of which is in the range 1–10 mm. The 65-mm-diameter discs appear as polycrystals with large grains. The electrical properties strongly depend on the presence of voluntarily introduced dopants to obtain high-resistivity material. Two different impurities are commonly used to obtain resistivity in the 10¹⁰ Ωcm range: aluminum and chlorine. Characterization of both doped materials and results of detectors under x-ray and γ-ray illumination will be given; spectrometric grade performance has been obtained and will be presented. The originally 65-mm-diameter crucible can be scaled up to 300 mm in diameter; this will be discussed in the paper.     

Uniformity and reproducibility studies of low-pressure-grown Cd<Subscript>0.90</Subscript>Zn<Subscript>0.10</Subscript>Te crystalline materials for radiation detectors

A large number of room-temperature detectors have been produced from CdZnTe crystals grown with 10% Zn and 1.5% excess tellurium by the low-pressure, vertical-Bridgman technique. Radiation spectra obtained by these crystals using a ²⁴¹Am source reveal the characteristic 59.5-keV line as well as the six low-energy peaks, which include the Cd and Te escape peaks. Similarly, ⁵⁷Co spectra obtained also show a very well-defined 122-keV peak with a 3:1 peak-to-valley ratio. Seven CdZnTe crystals have been grown for reproducibility studies. Four of these crystals have resistivities over 1E9 Ω-cm. Considering that the indiumdoping level is on the order of 2E15 cm⁻³, the reproducibility is excellent. The theoretical basis of the high-resistivity phenomenon in CdZnTe is discussed in reference to a previous paper. The uniformity of these 6-in.-long CdZnTe crystals is studied, and various measurements are carried out, both laterally and vertically, along the boule. It is determined that, in general, roughly a 3.5-in. section near the middle of the 6-in. boule has sufficient resistivity for producing radiation detectors. This nonuniformity along the vertical direction is caused mostly by the composition change of Cd, Zn, Te, and In-doping level in the growth melt caused by differences in the segregation coefficients of these elements. Although, variations in resistivity are seen across some of the wafer slices, most show very good uniformity with high breakdown voltage. Some of the variations are attributed to the different grains within the boule. Similar results are seen in the measured radiation spectra obtain on 4 mm × 4 mm × 2 mm samples from different locations across the wafer, where some samples show well-resolved secondary peaks, while others display only the primary spectral lines.     

Vapor phase equilibria in the Cd1−xZnxTe alloy system

Cd_1−xZn_xTe compounds of different compositions have been prepared at temperatures ranging from 400 to 1000°C by annealing elemental Te in sealed quartz ampoules, in an atmosphere comprising vapors of Cd and Zn whose partial pressures were varied by varying the composition of the binary Cd_1−yZn_y alloys which provided the Cd and Zn vapors in these annealing experiments. The chemical compositions of the resulting Cd_1−xZn_xTe compounds have been analyzed using electron probe microanalytical techniques. Results indicate that presence of a 0.5%Zn along with Cd in a closed or semi-closed system may prove to be beneficial in preventing decomposition and/or formation of a metal/non metal phase during annealing of Cd_0.96Zn_0.04 Te substrates. Using the thermodynamic data in the literature for the binary Cd_1−yZn_y alloys and with the assumption that the activities of the Cd and Zn components are weakly dependent on temperature, the partial pressures of Cd and Zn in equilibrium with the Cd_1−xZn_xTe compounds at various temperatures have been evaluated.     

采用不同材料坩埚对碲锌镉晶体质量的影响

文中采用热解氮化硼（pBN）坩埚生长Cd0．96Zn0．04Te单晶体，并与采用内壁涂碳的石英坩埚生长的晶体进行了对比分析。本文获得的晶体尺寸为φ45mm×110mm，（111）衬底晶片面积最大可达40mm×30mm，测试分析结果显示：Everson腐蚀坑密度小于2×10^4cm^-2，且分布均匀，无网络状分布结构，与石英熏碳坩埚相比，结构质量有了明显提高；第二相夹杂物尺寸小于2μm，密度为0～1×10^3cm^-3；（111）B晶片的X—ray反射貌相图显示，晶体的结构均匀，完整性较好。上述晶体质量评价指标均优于采用石英熏碳坩埚生长获得的晶体，而且更为重要的是，上述各项指标在同一晶锭的各晶片上基本重复，这说明了单晶具有良好的均匀性，有利于生长均匀的碲镉汞外延层。