碲锌镉探测器载流子屏蔽效应非线性变化研究

Pixellated CdZnTe Detector Based Investigation for Non-Linear Variation of Screening Effect Caused by Accumulated Carriers

搭建了基于像素阵列碲锌镉晶体的辐射成像探测系统，采用X射线源完成了不同管电压条件下的成像探测实验。实验结果表明，在保持较高辐照通量的条件下，管电压的增大会导致探测器出现范围逐渐扩大的无信号响应屏蔽区域，无响应区域边缘像素出现非线性信号变化。进一步通过建立探测器有限元模型，求解了第一类边界条件电势泊松方程，仿真模拟了不同特征光子能量及线性衰减系数条件下，碲锌镉晶体内部电势及电场分布。仿真结果表明，随着入射光子能量及线性衰减系数的变化，辐照中心的晶体内部出现相对高电势区域，造成电子载流子迁移路径出现扭曲而使得相应位置像素电极无法获得载流子感应电荷信号；而晶体内部相对高电势区域范围的非线性变化，是信号屏蔽区域边缘的像素单元信号随着入射光子能量的增加出现非线性变化的主要原因。

With different X-ray tube voltages the imaging screening effect of the pixellated CdZnTe detector is investigated under the ultrahigh irradiance. Moreover, a novel fluctuation process of the screening effect has been observed. Measurement results reveal that event counts of pixels which are distributed at the edge of the irradiated area experience a sudden increase followed by a continuous decrease when the tube voltage rises from 15 kV to 45 kV. Based on the Poisson equation, a theoretical model of the CdZnTe detector solved by the finite element method is developed which enables the penetrating investigation of the carrier collection in the CdZnTe crystal. A comparison between model simulations and test results shows that pixels in the central irradiated area are completely screened under increasing incident photon energy and linearity attenuation parameter. This is because the emergence of the relatively higher potential region, which is caused by the increasing of incident photon energy and linearity attenuation parameter, leads to the twist of the electron drift way. Furthermore, with the increase of the incident photon energy, the inconsecutive expansion of the accumulated carrier scope results in the fluctuation of the event counts of pixels distributed around the screening area. The imaging results deduced from the simulations are well consistent with the experimental data.