Study of micro-germanium pixel detector under a moderate cryogenic condition

锗探测器由于具有较高的能量分辨率和探测效率，被广泛用于探测高能x射线光子。但实际应用中，锗探测器的特征能量较低（0.67 eV），必须在液氮温度下工作。众所周知，给定锗探测器的暗电流图由大电流和表面漏电流组成。另一方面，电离粒子产生的电子-空穴对的密度数与探测体积无关，随着电离粒子能量的增加而增加，并局限在几百μm以内。此外，对于本研究中假设的像素尺寸（100 μm×100 μm）的电极，由于噪声电流与每个像素电极覆盖的半导体体积成正比，因此噪声电流应降低到每个像素小于100 nA。我们已经证实，在一个体积为1 mm×1 mm×1 mm的微小锗探测器中，噪声电流在室温下已经降低到10 μA。在这项研究中，我们研究了一个像素为60×97，尺寸为172 μm×172 μm的像素化锗传感器。该结果在2005年10月23-29日于波多黎各举行的IEEE会议上以“锗探测器的像素化效应及其温度依赖性”为题进行了讨论。

Germanium detectors are widely in use for detecting high energy X-ray photons, both because of the high energy resolution and because of high detection efficiency. However, it is a disadvantage in practice that Germanium detectors have to be operated at liquid nitrogen temperature due to the low characteristic energy (0.67 eV). It is well known that the dark current drawing in a given Germanium detector consists of the bulk current and the surface leakage one. The number of density of electron-hole pairs generated by ionizing particles is, on the other hand, independent from the detection volume, increases with the energy of ionization particles, and localized within a few hundreds μm. With an electrode as small as the pixel size assumed in the present work (100 μm×100 μm), furthermore, the noise current should be reduced less than 100 nA per pixel, since it is proportional to the volume of the semiconductor each pixel electrode covers.We have confirmed that the noise current is already reduced to 10 μA at room temperature in a tiny germanium detector with a volume of 1 mm×1 mm×1 mm. In this study, we have investigated a pixilated Germanium sensor with 60×97 pixels of size 172 μm×172 μm. The result was talked as the title "Pixilation Effect on Germanium Detectors and Their Temperature Dependencies" in the IEEE conference : the Nuclear Science & Symposium & Medical Imaging Conference, Puerto Rico, October 23-29,2005.