CdZnTe晶片的性能测试

测试了多个Cd0．9Zn0．1Te晶片的性能，包括红外透过率、成分分布、位错密度、Te沉淀／夹杂密度以及电阻率。研究表明，红外透过率与性能有着密切的联系：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、位错密度以及电阻率的情况。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。     

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。     

Cd气氛退火对CdZnTe晶片质量影响

在CdZnTe晶体生长时,有时会产生大颗粒的沉积相,严重的影响了CdZnTe晶片的质量,通过电子探针测试证明其为Cd沉积相。采用Cd气氛退火来消除Cd沉积相,可以改善CdZnTe晶片的质量。实验发现：在较高的温度（600℃）条件下,退火可以有效的消除大颗粒（〉5μm）的Cd沉积相,改善CdZnTe晶片红外透过率、X射线双晶回摆曲线半峰宽（FWHM）和腐蚀坑密度（EPD）。在此条件下对CdZnTe晶片进行退火,有助于提高CdZnTe晶片的性能。     

紫外探测器用CdS晶片制备工艺研究

介绍了叠层紫外/红外双色探测器结构特点、工作原理及选择CdS晶体材料制作紫外探测器光敏元的理论依据。阐述了CdS晶片制备及表面抛光质量的重要性和必要性。针对磨抛工艺对CdS紫外探测器性能的影响进行了研究。对比了几种抛光液对晶片表面的抛光效果,并进行了扫描电镜、红外透过率和表面粗糙度分析,得到了抛光后晶片表面的扫描电子显微镜(SEM)照片和CdS晶片厚度与红外透过率的关系曲线及CdS晶片厚度与振动噪声的关系。通过理论和实践的结合,确定了最佳抛光材料及最佳晶片厚度,研制出了完全能满足紫外探测器工艺要求的CdS探测器晶片。     

PBN坩埚生长碲锌镉单晶的性能与缺陷研究

采用垂直布里奇曼法,利用热解氮化硼(PBN)坩埚生长碲锌镉单晶(CdZnTe),并对晶体进行定向、切割与磨抛制成(111)面碲锌镉晶片。采用傅里叶红外透过光谱仪、红外透射显微镜、金相显微镜、X射线形貌仪、X射线衍射仪和X射线双晶衍射仪等仪器系统地检测和研究了碲锌镉晶体的性能与缺陷。研究发现:相比于石英坩埚,采用PBN坩埚生长的碲锌镉晶体单晶率和出片率均大幅增加,孪晶、小角晶界和位错密度明显减少。     

表面处理对Au-CdZnTe电极接触性能的影响

碲锌镉(CdZnTe)是制备X射线、γ射线探测器的一种理想半导体材料。CdZnTe欧姆接触电极是制备CdZnTe核辐射探测器的关键技术之一。表面加工状态是影响欧姆接触性能的重要因素,文中研究了4种表面处理工艺对Au-CdZnTe电极接触性能的影响。研究发现对晶片表面进行溴甲醇腐蚀处理和机械化学抛光均有助于提升Au-CdZnTe电极欧姆接触性能。对晶片进行机械化学抛光后再进行溴甲醇腐蚀处理,使用这种晶片所制备的电极具有更加优良的综合电学性能。     

退火对CdZnTe晶体质量的影响

我们用红外透射光谱和X射线双晶衍射等，研究了退火对CdZnTe晶体质量的影响．结果表明，在Cd气氛中，700℃，退火5小时以上，能大量地去除晶片中的Te沉淀，提高其红外透射比；同时，退火也导致了晶片表面的损伤，损伤层为50～130μm．表面结构损伤的原因是，（1）Cd气氛中退火，CdZnTe晶体表面的Zn损失；（2）退火过程中，吸附在沉淀物周围的杂质，尤其是快扩散杂质，将随着沉淀相的消失而迁移到晶体的表面，从而破坏了表面的晶体结构．退火后，磨去损伤层，可将聚集在表面的这些杂质除去，更有利于外延生长或器件制备．     

高阻CdZnTe晶体的退火处理

获得高电阻率的、完整性好的CdZnTe晶体是研制高性能的CdZnTe γ射线探测器的关键.运用热力学关系估算了Cd1-xZnx熔体平衡分压,尝试以Cd1-xZnx合金源替代Cd源进行Cd0.8Zn0.2Te晶片的热处理,研究了退火对Cd0.8Zn0.2Te晶片质量的影响.结果表明：在1069K下用Cd0.8Zn0.2合金源（PZn=0.122×105Pa和PCd=1.20×105Pa）对Cd0.8Zn0.2Te晶片退火5天以上,可提高晶体电阻率一个数量级和晶体红外透过率10%以上,并可消除或减小晶片中的Te沉淀,同时避免了Zn的损失,改善Zn的径向分布.可见,采用Cd1-xZnx合金源代替Cd源控制进行CZT退火处理优于仅采用Cd源控制的退火处理.     

Cd1-xMnxTe晶体衬底的红外透过性能

研究了生长态和退火后Cd1-xMnxTe晶片的吸收边和红外透过性能.Cd1-xMnxTe晶体采用垂直Bridgman法生长,获得面积为30 mm×40 mm的(111)面Cd1-xMnxTe单晶片;晶片在Cd气氛下退火.近红外光谱表明,吸收边的截止波长反映晶片的Mn含量范围为0.1887≤x≤0.2039,其中轴向成分波动差值约为0.0152,径向成分波动差值约为0.0013;x=0.2的Cd1-xMnxTe晶体吸收边的吸收系数变化范围为2.5～55 cm-1;退火后,晶体的吸收边位置没有变化,表明晶片中Mn含量未受到退火的影响.傅里叶变换红外透射光谱表明,晶片在红外光波数为4000～500 cm-1范围的红外透过率为45%～55%;退火后,晶片的红外透过率提高到61%以上,接近理论值65%.     

CdZnTe晶体生长条件的选取

本文通过理论分析和计算,给出了生长CdZnTe晶体的优选生长条件,实验结果表明,用该生长条件制备出质量较好的CdZnTe晶体,晶锭表面光亮,无孔洞气泡等宏观缺陷,含单晶率≥30％,位错密度≤10~4cm~(-2),最大红外透过率～65％。     

Cd1-xZnxTe合金的退火研究

用红外透射谱和喇曼散射谱研究了退火对 Cd1 - x Znx Te晶片中 Te沉淀的影响 .研究结果表明 ,红外透射谱只对大尺寸的 Te沉淀较为敏感 ,而喇曼散射谱却能够探测到样品中小尺寸的 Te沉淀 ,两者互为补充 .在 Cd气氛下对晶片进行退火处理 ,选择合适的退火温度和退火时间 ,可以有效地消除晶片中大尺寸的 Te沉淀 ,却难以消除晶片中小尺寸的微量 Te沉淀     

Infrared absorption behavior in CdZnTe substrates

Infrared (IR) optical transmission measurements of polished CdZnTe wafers can provide useful information about excess impurities, stoichiometry, and inhomogeneities (precipitates and inclusions). We have investigated the IR transmission behavior of Cd_0.96Zn_0.04Te between 8 m and 20 m at room temperature. The measurements were made before and after thermal treatments involving control of the Cd and Zn overpressures, which served to minimize the Cd (cation) vacancy population. Our results support the polar optical phonon scattering theory of Jensen, according to which the absorption in donor dominated CdZnTe varies as^m with m=3. For material dominated by acceptors, we show that the theoretical absorption by inter-valence band transitions can be approximated by a similar power law with exponent m=1, and that Cd-vacancy dominated wafers are in reasonable agreement with this. We find some wafers in which the asgrown condition exhibits partial compensation of impurity donors by Cd vacancy acceptors, and demonstrate removal of the compensation by annealing to fill the vacancies. In a separate group of wafers, we find that an observed increase in absorption occurring during growth of a HgCdTe layer by liquid phase epitaxy can be explained in terms of an increase in Cd vacancies caused by diffusion of Cd to Te precipitates. This effect can be reversed by annealing in Cd−Zn vapor, which fills vacancies and eliminates some precipitates. Impurity concentrations were measured by glow discharge mass spectrometry (GDMS).     

Thermomigration of Te precipitates and improvement of (Cd,Zn)Te substrate characteristics for the fabrication of LWIR (Hg,Cd)Te photodiodes

(Cd,Zn)Te wafers containing Te precipitates have been annealed under well defined thermodynamic conditions at temperatures below and above the melting of Te. Results of the examination of the wafers with infrared microscopy before and after the anneals indicate a substantial reduction of the Te precipitates in wafers annealed at temperatures in excess of the melting point of Te compared with those annealed at temperatures below the melting point of Te. These results confirm the thermomigration of liquid Te precipitates to be the principally operative mechanism during annealing in the elimination of these precipitates in (Cd,Zn)Te wafers. The occurrence of Te precipitates in (Hg,Cd)Te epitaxial layers grown on (Cd,Zn)Te substrates containing Te precipitates is also explained on the basis of thermomigration of these precipitates during LPE growth from the substrates to the epilayers. Absence of occurrence of Te precipitates in (Hg,Cd)Te epilayers grown on annealed (Cd,Zn)Te substrates with negligible Te precipitates is also confirmed. Usefulness of annealing (Cd,Zn)Te substrates—to eliminate Te precipitates—prior to epilayer growth is confirmed via demonstration of improved long wavelength infrared (Hg,Cd)Te device array performance uniformity in epitaxial layers grown on (Cd,Zn)Te substrates with negligible Te precipitates after annealing.     

Advancements in THM-Grown CdZnTe for Use as Substrates for HgCdTe

The focus of this work is to evaluate the suitability and substrate potential of Cd_0.9Zn_0.1Te and Cd_0.96Zn_0.04Te crystals grown by the traveling heater method (THM). THM-grown Cd_0.9Zn_0.1Te crystals used for gamma spectroscopy have shown very good spectral performance owing partly to the very low concentration of Te inclusions and precipitates. Inspection in the infrared (IR) of annealed THM-grown CdZnTe wafers reveals no inclusions >3 μm, and Fourier-transform infrared measurements show IR transmission values in excess of 60%. Wafer etch pit density values are typically less than 4 × 10^?4 pits/cm², and double-crystal x-ray rocking-curve measurements show full-width at half-maximum values approaching 40 arcsec. 〈211〉 wafers have been produced with off orientation within 0.3°. (111)-Oriented, seeded THM growth runs have the ability to provide 10 60 mm × 60 mm × 2 mm wafers from a 75-mm-diameter boule or 20 90 mm × 90 mm × 2 mm wafers from a 100-mm-diameter boule.     

CdZnTe晶片中沉积相分布特性的研究

利用红外显微镜分别对富Cd和富Te配料生长的两组碲锌镉晶片的沉积相进行观察,对观察结果做统计分析,发现两组晶片中的沉积相在形状和分布情况方面有很大差别,采用数据拟合的方法发现两组CdZnTe晶片中不同尺寸的沉积相颗粒的密度满足指数分布.     

Reduction of CdZnTe substrate defects and relation to epitaxial HgCdTe quality

We have conducted annealing experiments on CdZnTe wafers to restore stoichiometry, eliminate or reduce second-phase (Cd or Te) inclusions, and investigate effects on the quality of epitaxial HgCdTe grown on the thermally treated substrates. Two categories of second phase features were revealed in these materials. Category 1 has a star-like shape with sixfold symmetry (as seen by infrared transmission microscopy) and a central core consisting of cadmium. These stars were observed only in the more stoichiometric materials (having good infrared transmission characteristics). Category 2 consists of triangular, hexagonal, and irregular shaped tellurium inclusions which are present in the off-stoichiometry materials (which exhibit strong IR absorption). Substrates were annealed at temperatures ranging from 500 to 700°C for one to seven days, in vapor derived from elemental Cd or Cd_1-xZn_x alloy (x = 0.005). These anneals were able to eliminate the excess IR absorption and decrease the apparent sizes of both categories of second-phase features. It was found that pinhole-like morphological defects on the surface of a HgCdTe layer grown by liquid phase epitaxy can be caused by Cd and Te inclusions located within the CdZnTe substrate near the interface. Additionally, measurement and spatial mapping of copper concentration by sputter initiated resonance ionization spectroscopy showed 10 to 100 times higher Cu concentration in the inclusions than in the surrounding matrix areas.     

固液界面附近CdZnTe晶体组份分布及X-Ray测试

利用对垂直布里奇曼Bridgman法生长中的Cd1-xZnxTe晶体停电自然降温的方法获得了具有不同凝固速率的同一块单晶样品.通过红外透射光谱测量方法对停电自然降温前后的单晶区域进行比较,结果显示：停电自然降温后,在固液界面附近存在一个明显的组份过度区,正常凝固的晶体组份分布比较均匀,而快速凝固的结晶区域轴向组份分布梯度较大,同时,通过X-Ray测试结果进一步准确判断固液界面的位置.