Development of highly reliable contacts on p-type CdTe for radiation detectors

碲化镉（CdTe）是一种用于X射线和γ射线辐射探测器的有吸引力的半导体材料。CdTe的优点是它具有大的带隙能量（~ 1.6eV）和高的平均原子序数（Z_<cdTe>=50）。然而，由于CdTe中空穴的低迁移率和短寿命，大量的电荷损失导致探测器中能量分辨率的降低。为了完成电荷收集，必须在CdTe探测器中施加非常高的偏置电压。因此，肖特基接触，提供非常低的泄漏电流与高偏置电压，需要实现高分辨率的CdTe探测器。虽然传统的方法来制造肖特基接触的p型碲化镉涉及使用具有低功函数的金属，如铟（In），在器件操作过程中的检测性能的时间依赖性退化，称为“极化效应”，经常观察到的碲化镉探测器与肖特基接触。为了将CdTe应用于实际的研究， 关于我们 辐射探测器，必须开发具有低漏电流的高稳定肖特基接触。第一个目标是研制高可靠性的碲化镉辐射探测器肖特基铟接触。第二是通过X射线衍射（XRD）和透射电子显微镜（TEM）分析在不同衬底温度下沉积的In膜的界面微观结构来理解肖特基In接触的形成机制。这些研究结果将为我们开发用于辐射探测器的p型CdTe肖特基接触提供指导。在In沉积过程中对CdTe进行热处理显著降低了泄漏电流，提高了其稳定性。XRD分析表明，In原子与CdTe反应生成In_4Te_3或InTe，反应温度T_S&gt;200℃。采用较高的T_s淀积方法制备的InTe接触大大提高了探测性能的稳定性。TEM观察表明，CdTe辐射探测器的漏电流和稳定性与接触/CdTe界面的微观结构密切相关。少

Cadmium telluride (CdTe) is an attractive semiconductor material for X-ray and γ-ray radiation detectors. The advantages of CdTe are that it has a large bandgap energy (〜1.6eV) and a high average atomic number (Z_<cdTe>=50). However, due to the low mobility and short lifetime of holes in CdTe, a considerable amount of charge loss causes reduction of energy resolution in the detector. For a complete charge collection, very high bias voltage must be applied in the CdTe detectors. Thus, Schottky contacts, which provide very low leakage current with a high bias voltage, are required to achieve high resolution in CdTe detectors. Although the conventional approach to fabricate Schottky contacts for p-type CdTe involves the use of metals with low work function, such as indium (In), the time-dependent degradation of detection performance during device operation, known as "polarization effect", is often observed in the CdTe detectors with Schottky contacts. In order to apply CdTe to practical r … More adiation detector, highly stable Schottky contacts with low leakage current must be developed.The purpose of the present study is twofold. The first is to develop of highly reliable Schottky In contacts for CdTe radiation detectors. The second is to understand the Schottky In contact formation mechanism by analyzing interfacial micro structure of the In films which were deposited at various substrate temperatures using X-ray diffraction (XRD) and transmission electron microscopy (TEM). These studies will provide us a guideline for developing Schottky contacts for p-type CdTe which would be used hi the radiation detectors.The thermal treatment of the CdTe during the depositions of In remarkably decreased the leakage current and improved its stability. XRD analysis showed that In atoms reacted with CdTe forming In_4Te_3 or InTe during the depositions with T_S>200℃. The InTe contacts, which were prepared by the depositions with rather high T_s, drastically improved the stability of the detection performance. TEM observations revealed that the leakage current and the stability of the CdTe radiation detectors were strongly correlated with the micro structure of contact/CdTe interfaces. Less