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

碲化镉(Cd Te)是一种极具吸引力的X射线和γ辐射探测器半导体材料。CdTe的优点是它具有大的带隙能(~1.6 eV)和高的平均原子序数(Z&lt；CdTe&Gt；=50)。然而，由于CdTe中空穴的迁移率低，寿命短，大量的电荷损失会降低探测器的能量分辨率。对于完整的电荷收集，必须在CdTe探测器中施加非常高的偏置电压。因此，需要肖特基接触在高偏置电压下提供非常低的泄漏电流，以便在CdTe探测器中实现高分辨率。尽管制备p型CdTe肖特基接触的传统方法涉及使用具有低功函数的金属，例如铟(In)，但在具有肖特基接触的CdTe探测器中，经常观察到在器件工作期间检测性能的随时间变化的退化，即所谓的“极化效应”。为了将碲化镉应用于实际的r-…必须开发更多的辐射探测器、高稳定的、低泄漏电流的肖特基接触。首先是研制高可靠性的肖特基In触头，用于镉镉辐射探测器。二是通过对不同衬底温度下沉积的In薄膜的界面微观结构的分析，了解肖特基接触形成的机理。这些研究将为研制用于辐射探测器的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，可以显著降低漏电流，提高其稳定性。X-射线衍射分析表明，在T_S&GT；200℃沉积过程中，In原子与Cd Te反应生成In4Te或InTe。用具有较高T_S的沉积层制备的INTE触点，大大提高了检测性能的稳定性。透射电子显微镜观察表明，漏电流和辐射探测器的稳定性与接触/CdTe界面的微观结构密切相关。较少

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