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

碲化镉（CdTe）是一种有吸引力的x射线和γ射线辐射探测器的半导体材料。CdTe的优点是具有较大的带隙能量（~ 1.6eV）和较高的平均原子序数（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的能量分辨率降低。为了完成电荷收集，必须在CdTe探测器上施加非常高的偏置电压。因此，肖特基触点可以在高偏置电压下提供非常低的漏电流，因此需要在CdTe探测器中实现高分辨率。尽管制造p型CdTe肖特基触点的传统方法涉及使用具有低功函数的金属，如铟（In），但在器件运行期间检测性能的时间依赖性退化，称为“极化效应”，经常在具有肖特基触点的CdTe探测器中观察到。为了将碲化镉应用到实际的高辐射探测器中，必须开发出高稳定、低泄漏电流的肖特基触点。本研究的目的是双重的。首先是为CdTe辐射探测器开发高可靠的肖特基接触。二是利用x射线衍射仪（XRD）和透射电镜（TEM）分析不同衬底温度下沉积的In膜的界面微观结构，了解Schottky In接触形成机理。这些研究将为开发p型碲化镉的肖特基触点提供指导，该触点将用于辐射探测器。在沉积铟的过程中对碲化镉进行热处理，可以显著降低漏电流，提高其稳定性。XRD分析表明，在200℃的T_S沉淀过程中，In原子与CdTe反应生成In_4Te_3或InTe。通过高T_s沉积制备的InTe触点，极大地提高了检测性能的稳定性。透射电镜观察表明，CdTe辐射探测器的泄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