CdZnTe像素阵列探测器成像评价模型及实验

Carrier-trapping-based imaging evaluation model and experiment of pixellated CdZnTe detector

考虑载流子陷获效应建立了碲锌镉(CdZnTe)像素阵列探测器感应电荷分布模型,并从非平衡载流子连续方程出发,推导了晶体内部陷获载流子数密度分布,得到了CdZnTe探测器成像调制传递函数评价模型。数值计算结果表明:随入射光子能量的增加,探测器成像质量明显下降;当电子载流子与空穴载流子迁移寿命积范围分别为0.5×10-3～5.0×10-3 cm2/V,2.0×10-5～7.5×10-5 cm2/V时,电子载流子感应信号是探测器响应信号的主要来源,而空穴迁移寿命积变化对探测器成像性能的影响有限,所建立模型的载流子收集特性与实际探测器载流子收集特性相符。搭建了40mm×40mm的CdZnTe成像探测系统,探测并获得了系统预采样调制传递函数。实验结果表明:模型理论值与实验数据相符合,实际CdZnTe晶体中存在的固有深能级缺陷、实验所采用的非单色性X射线源及较大的实际像素间隙是造成理论值与实验结果存在一定偏差的主要原因。

A flexible induced charge model of CdZnTe pixellated detector is presented.This model takes into account the charge trapping effect in the detection process.The distribution of the trapped carriers in CdZnTe crystal is derived based on the continuity equations.In consequence,an evaluation model based on the presampling modulation transfer function（presampling MTF） is obtained.As shown through the numerical simulation,the detector imaging quality decreases obviously with the increase in incident photon energy.When the electron-and hole-mobility lifetime products are 0.5×10-3 to 5.0×10-3 cm2/V and 2.0×10-5 to 7.5×10-5 cm2/V,respectively,the model signal is almost due to the electron transport,and the hole transport contributes relatively little to the model signals.The carrier collection characteristics of the model correspond with the practical single polarity characteristics of the pixellated CdZnTe detector.Moreover,a 40 mm×40 mm CdZnTe imaging system has been established.The experimental data based on the obtained presampling MTF show that the simulation results are consistent with the experimental data well.The discrepancies between the simulated results and the experimental data are mainly attributed to the intrinsic deep level trapping centers,the poly-energetic X ray source that has been applied in the experiment and the practical pixel gap.