Investigation of Cadmium Manganese Telluride Crystals for Room-Temperature Radiation Detection

Cadmium manganese telluride (CMT) has high potential as a material for room-temperature nuclear-radiation detectors. We investigated indium-doped CMT crystals taken from the stable growth region of the ingot and compared its characteristics with that from the last-to-freeze region. We employed different techniques, including synchrotron white-beam x-ray topography (SWBXT), current–voltage (I–V) measurement, and low-temperature photoluminescence spectra, and we also assessed their responses as detectors of radiation exposure. The crystal from the stable growth region proved to be superior to that from the last-to-freeze region; it is a single-grain crystal, free of twins, and displayed a resistivity higher by one order of magnitude. The segregation of indium dopant in the ingot might be responsible for its better resistivity. Furthermore, we recorded a good response in the detector fabricated from the crystal taken from the stable growth region; its (μτ)_e value was 2.6 × 10⁻³ cm²/V, which is acceptable for thin detectors, including their application in medicine.     

碲锌镉晶体中微观缺陷分析

碲锌镉晶体(CdZnTe)是一种性能优异的红外焦平面探测器衬底材料,其质量的优劣将直接影响外延层的结构与性能,而晶体中的微观缺陷常常是影响衬底材料质量的主要因素之一.本文采用红外透射显微镜、金相显微镜、X射线形貌仪、扫描电镜、白光干涉仪等仪器系统地检测和研究了碲锌镉晶体中存在的微观缺陷.研究发现碲锌镉晶体样品中主要存在层错、孪晶界和包裹物等微观缺陷,结合晶体缺陷理论详细地分析了碲锌镉晶体中微观缺陷的形成机制.     

Internal Electric Field Behavior of Cadmium Zinc Telluride Radiation Detectors Under High Carrier Injection

The behavior of the internal electric field of nuclear-radiation detectors substantially affects detector performance. We investigated the distribution of the internal field in cadmium zinc telluride (CZT) detectors under high carrier injection. We noted the build-up of a space-charge region near the cathode that produces a built-in field opposing the applied field. Its presence entails the collapse of the electric field in the rest of the detector, other than the portion near the cathode. Such a space-charge region originates from serious hole trapping in CZT. The device’s operating temperature greatly affects the width of the space-charge region. With increasing temperature from 5°C to 35°C, its width expanded from about one-sixth to one-half of the total depth of the detector.     

Vapor-Phase Growth of Bulk Crystals of Cadmium Telluride and Cadmium Zinc Telluride on Gallium Arsenide Seeds

The growth of large-area bulk crystals of cadmium telluride and cadmium zinc telluride has been demonstrated using the combination of a novel physical vapor transport growth system and heteroepitaxial seeding on GaAs wafers. X-ray diffraction studies show the resulting material to be of extremely high quality despite the large lattice mismatch between the seed and the grown crystal. This process should provide a reliable growth route for large-area large-volume single-crystal boules of cadmium telluride and cadmium zinc telluride.     

碲锌镉晶片退火的显微Raman光谱分析

测量了4块不同退火条件处理碲锌镉晶片的显微Raman光谱,观察到了与碲锌镉材料及材料中Te沉积晶格振动相对应的Raman散射峰,发现了位于327 cm-1/332 cm-1的新峰.通过对碲锌镉晶片进行退火处理,有效的消除了Te沉积,比较碲锌镉晶片退火前后的显微Raman光谱,指出327 cm-1/332 cm-1散射峰只可能由来源于类CdTe或类ZnTe的二级声子散射引起,与碲锌镉材料中的Te沉积无关.     

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。     

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45mm×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2×104cm-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0～1×103cm-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。     

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φ455mm×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2×104cm-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0～1×103 cm-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.     

Large-Format and Long-Wavelength Infrared Mercury Cadmium Telluride Detectors

Due to continuous improvement of traditional liquid-phase epitaxy n-on-p technology, excellent mid-wavelength infrared HgCdTe (MCT) detectors with 1280 × 1024 pixels and 15 μm pitch size have been produced at AIM. At an operating temperature (T _OP) of 80 K, a noise equivalent temperature difference (NETD) of 17.8 mK and an operability of 99.96% have been obtained. At T _OP = 130 K, the operability remains high at 99.58%. On the basis of these results, the sensitivity of this detector design has been extended into the long-wavelength infrared (LWIR) region, obtaining a detector with an NETD of 30.4 mK and an operability of 99.81% at T _OP = 80 K. In parallel, the growing maturity of molecular-beam epitaxy (MBE) growth of MCT on GaAs substrates has led to an improvement of the performance of the MWIR 640 × 512, 15-μm-pitch detector from an operability of 99.30% in 2011 to 99.83% recently.     

Effect of Colloidal Silver on Optical Transmittance Characteristics of Bulk Cadmium Zinc Telluride Crystals

Colloidal silver is observed to affect the transmittance of p-type Cd_1−y Zn _y Te (CZT) single-crystal substrate material at room temperature. The optical transmittance spectra have been analyzed in the near-infrared (NIR) and mid-infrared (MIR) regions. The transmittance characteristics of CZT showed significant reduction in absorption due to split-off valance band transitions in the NIR region and intervalence band absorption in the MIR region upon coating CZT substrates with silver paste. This reduction in absorption has been explained to be due to the compensation of the acceptor defects (native and foreign). Silver atoms incorporated from the silver coating help in compensation of these defects. A similar effect on transmittance characteristics of mercury cadmium telluride (MCT) epilayers grown on CZT substrates after coating silver paste on the CZT substrate side was also observed. An improvement in the transmittance of CZT substrates after the application of silver paste was observed. A similar improvement in transmittance is usually achieved by annealing the substrates in a Cd/Zn atmosphere. The results are explained by considering the formation of neutral complexes of acceptors (cadmium vacancies) and the interstitial silver. This study also points to the important conclusion that silver paste on CZT should be applied with caution for measurement purposes since it diffuses even at room temperature and modifies the optical characteristics.     

碲硒锌镉单晶体的垂直布里奇曼法生长与性能研究

碲锌镉(CdZnTe)是目前最重要的室温半导体核辐射探测器材料。而在CdZnTe晶格中以Se替位部分Te得到碲硒锌镉(CdZnTeSe),将使得晶格中离子键的成分增加,从而提高晶体的硬度,降低Cd空位和Te夹杂物缺陷浓度,提升材料质量。为了获得适宜于核辐射探测器制备的CdZnTeSe晶体,研究了富Te条件下CdZnTeSe晶体的垂直布里奇曼法生长,成功制备出直径为21 mm、长度超过70 mm的Cd_0.9Zn_0.1Te_0.97Se_0.03单晶锭。所得Cd_0.9Zn_0.1Te_0.97Se_0.03晶体的(110)面X射线衍射摇摆半峰宽达到0.104°,而Te夹杂相的尺寸小于5μm,表明晶体具有良好结晶性。Cd_0.9Zn_0.1Te_0.97Se_0.03晶锭尾部的能带隙和红外透过率均低于晶锭的头部和中部,这可归因于Cd_0.9<...     

甚长波碲镉汞红外探测器的发展

天基红外技术对于远程弹道导弹防御具有重要作用.当飞来的导弹位于地球阴影区域时,作为背阳的结果,空间温度很低,导弹呈现为一个微弱的冷目标,峰值波长在甚长波红外(VLWIR,大于14μm)波段,这时就需要VLWIR探测器.VLWIR对于大面阵碲镉汞焦平面(FPA)器件的设计来说是一种非常具有挑战性的波段.它要求高均匀性、低缺陷率、高量子效率、低暗电流和低噪声.主要通过对近年来刊发的部分有关英语文献资料的归纳分析,介绍了有关VLWIR/MCT技术的发展状况,其中一个发展趋势是从n-on-p空位掺杂器件结构转向非本征掺杂p-on-n器件结构.     

分子束外延碲镉汞探测器的变结面积I-V测试研究

碲镉汞红外探测器的表面钝化处理对器件暗电流有较大影响,决定了器件的探测性能。为了研究表面钝化层不同生长方式对暗电流的抑制效果,使用分子束外延(Molecular Beam Epitaxy, MBE)系统在Si基衬底上生长碲镉汞材料,分别通过磁控溅射和原位钝化方法生长CdTe/ZnS钝化膜层。采用半导体工艺在碲镉汞材料上制备了变面积光伏探测器。通过测试不同钝化膜层器件的暗电流,分析零偏电阻和面积乘积(R₀A)与周长面积之比(p/A)的关系。结果表明,磁控溅射生长钝化层的Si基碲镉汞器件存在较大的隧穿电流,而原位钝化生长钝化层的Si基碲镉汞器件能更有效地抑制表面漏电流。拟合器件R₀A因子随PN结面积的变化,得出原位生长钝化层的器件具有更好的钝化效果。变面积器件的制备和测试能够有效且直观地反映器件性能。     

碲锌镉晶体表面磨抛方法研究

碲锌镉是一种性能优异的Ⅱ-Ⅵ族化合物半导体材料。随锌含量不同,其禁带宽度可连续调节,是用于制备红外探测器的碲镉汞材料的优良衬底。介绍了多种碲锌镉晶体的磨抛方法,包括手工研磨、机械抛光、化学抛光和机械化学抛光。借助多种表征技术和改良手段,碲锌镉晶体的表面加工取得了显著进步。     

碲锌镉晶片的机械化学磨抛分析

对<111>方向的三块碲锌镉晶片进行了不同的机械磨抛、化学机械抛光、化学抛光,在相同的测量条件下用三维形貌干涉仪进行表面监测.比较了碲锌镉晶片不同的磨抛方法对碲锌镉晶片表面机械损伤的情况,开展了碲锌镉晶片不同的磨抛方法对损伤的去除程度的对比实验,进行了碲锌镉晶片表面粗糙度及平整度实现的研究.     

碲镉汞器件空间辐射损伤研究的进展

碲镉汞(MCT)红外探测器在天基平台中的应用正在逐渐增多,运行于空间辐射环境这一特点给其功能实现带来了挑战.MCT器件的独特性质要求人们对空间辐射效应给予特别考虑.目前,通过利用CdTe钝化MCT探测器技术,器件的总剂量脆弱性问题已经得到解决.随着材料质量的改进(例如通过降低原生缺陷浓度),MCT器件更容易受到位移损伤...     

碲锌镉晶体生长炉温度场的一阶仿真

介绍了一种碲锌镉晶体生长炉温度场一阶仿真的实用方法。该方法基于传热学原理,利用蒙特卡罗法计算没有解析表达式的角系数,利用MATLAB的矩阵计算功能实现多变量线性代数方程组的求解,具有简单、易用的特点。     

Component Overpressure Growth and Characterization of High-Resistivity CdTe Crystals for Radiation Detectors

Spectrometer-grade CdTe single crystals with resistivities higher than 10⁹ Ω cm have been grown by the modified Bridgman method using zone-refined precursor materials (Cd and Te) under a Cd overpressure. The grown CdTe crystals had good charge-transport properties (μτ _e = 2 × 10⁻³ cm² V⁻¹, μτ _h = 8 × 10⁻⁵ cm² V⁻¹) and significantly reduced Te precipitates compared with crystals grown without Cd overpressure. The crystal growth conditions for the Bridgman system were optimized by computer modeling and simulation, using modified MASTRAPP program, and applied to crystal diameters of 14 mm (0.55′′), 38 mm (1.5′′), and 76 mm (3′′). Details of the CdTe crystal growth operation, structural, electrical, and optical characterization measurements, detector fabrication, and testing using ²⁴¹Am (60 keV) and ¹³⁷Cs (662 keV) sources are presented.     

超大面阵碲镉汞探测器低应力设计及有限元分析

随着碲镉汞材料和器件技术的不断发展,满足大视场、超高分辨率应用需求的超大阵列规模的红外探测器逐步投入工程应用,超大面阵探测器芯片的低温可靠性成为封装技术的重点研究内容。以某超大面阵碲镉汞混成芯片为研究对象,采用有限元仿真分析法研究了冷头材料体系、冷台外径、冷台的结构形式等因素对混成芯片低温应力和芯片光敏面低温变形的影响规律,最终优化设计出一套可满足超大面阵芯片低温可靠性要求的冷头结构和材料体系。仿真结果显示,该冷头体系硅电路低温下最大应力约为70 MPa,碲镉汞光敏区在低温下的变形约为30■m。仿真结果能满足工程应用可靠性要求的经验仿真阈值,有效改进了超大面阵红外探测器的高可靠小型化封装技术。     

支撑结构对碲锌镉固液界面形状的影响

在晶体生长过程中,固液界面形状与界面附近热流的状态有关。影响固液界面附近热流方向的因素有外部温场分布和材料热导率等。总结了常用的固液界面控制方式,然后采用CGSim温场模拟软件对3种使用不同支撑结构的晶体的生长过程进行了模拟,并对籽晶区以及锥形区内部固液界面的形状进行了对比。结果显示,支撑结构对籽晶区及锥形区内部固液界面的控制影响较大;通过采用合适的支撑结构设计并选取合适材料,同时配合外部温场的调节,能够得到理想的凸形固液界面。