Effects of Surface Processing on the Response of CZT Gamma Detectors: Studies with a Collimated Synchrotron X-Ray Beam

Using a microscale X-ray mapping technique incorporating a synchrotron beam, we are able to reveal the fine details of the surface properties in cadmium zinc telluride (CZT) semiconductor detectors. A detector, with various degrees of surface roughness, was irradiated by a high-spatial-resolution X-ray beam. The detector’s response was analyzed and displayed as a two-dimensional (2-D) map, and the charge collection was obtained from the peak positions in the spectra versus the beam’s location, which reflects the local material properties. We noted the correlation between the 2-D image and the spectral response of the charge collection at different locations on the surface area, which indicates that a rough surface tends to contain trapping centers, thereby enhancing leakage current and distorting the signal. We also discuss our observations on the transition effect at the boundary area of a rough and a smooth surface under identical conditions.     

Compensation and trapping in CdZnTe radiation detectors studied by thermoelectric emission spectroscopy, thermally stimulated conductivity, and current-voltage measurements

The thermal ionization energies of traps and their types, whether electron or hole traps, were measured in commercial CdZnTe crystals for radiation detectors. The measurements were done between 20 and 400K using thermoelectric emission spectroscopy (TEES) and thermally stimulated conductivity (TSC). For reliable results, indium ohmic contacts had to be used instead of gold Schottky contacts. For filling of the traps, photoexcitation was done at zero bias, at 20K, and at wavelengths which gave the maximum bulk photoexcitation. In agreement with theory, the TSC current was found to be on the order of times or even larger than the TEES current, where V is the applied bias in TSC and ΔT is the applied temperature difference in TEES. Large concentrations of hole traps at 0.1 and 0.6 eV were observed and a smaller concentration of electron traps at 0.4 eV was seen. The deep traps cause compensation in the material, which is desirable, but they also cause carrier trapping that degrades the spectral response of radiation detectors made from the material.     

Cd在Cd0．9Zn0．1Te晶体中的有效扩散系数与扩散激活能

为了计算Cd在Cd0.9Zn0.1Te(CZT)晶体中的有效扩散系数DCd与扩散激活能QCd,利用Cd在CZT晶体中的扩散特性,设计了在不同Cd压下对CZT的退火实验,推导出了晶体电阻率与Cd有效扩散系数之间的函数关系,经过计算,首次获得了在1073 K,973 K和873 K温度时Cd原子在CZT晶体中的有效扩散系数DCd,分别为1.464×10-10cm2/s,1.085×10-11cm2/s和4.167×10-13cm2/s.将扩散数据经过拟合后得到了Cd原子在CZT晶片中有效扩散系数的表达式2.33×exp(-2.38 eV/kT)(873 K～1073 K),其中扩散激活能QCd为2.38 eV.     

指数法拟合CZT探测器时间响应曲线

为探讨CZT探测器时间响应特性规律,采用指数拟合法分析CZT探测器对快脉冲X射线响应曲线下降沿衰减规律,并分析该衰减常数与电压、灵敏面积之间的关系。结果表明:10 mm×10 mm×2 mm与5 mm×5 mm×2 mm单晶CZT探测器对纳秒级脉冲X射线时间响应曲线下降沿均遵循单指数衰减规律,衰减常数为10~(-8)s数量级。随着电压升高,不同灵敏面积CZT探测器响应曲线衰减常数的差值降低。该结论可为揭示贯穿辐射条件下CZT晶体内部载流子输运规律提供依据。     

碲锌镉晶体生长全局热传递模拟模型准确度研究

在碲锌镉晶体生长技术开发方面,数值模拟软件发挥着越来越重要的作用。以全局热传递模型为基础进行晶体生长模拟能够极大的提高模拟结果的实用性,缩短晶体生长设备及生长工艺的开发周期。但其前提是采用的全局热传递模型的准确度较高。因此,本文主要研究了几何模型、物性参数、边界控温条件等对模型准确度的影响,并根据模型计算值与炉体中心测温比较结果,修正了上述模型各参数,获得了在多种温度设定条件下,计算结果都能与实际过程很好的吻合的全局热传递模型。采用修正后的模型应用于碲锌镉晶体生长过程模拟,最终晶体生长模拟结果的温度与实际监测温度差距在2 ℃以内。     

Surface passivation of cadmium zinc telluride radiation detectors by potassium hydroxide solution

The spectral resolution of cadmium zinc telluride (CZT) room temperature nuclear radiation detectors is often limited by the presence of conducting surface species that increase the surface leakage current. Surface passivation plays an important role in reducing this surface leakage current and thereby decreasing the noise of the detectors and improving the spectral energy resolution. Chemical etching with a Br-MeOH solution leaves CZT surfaces rich in Te and is considered as one of the primary causes of the increased surface leakage current. Previous studies have shown that hydrogen peroxide (H₂O₂) forms oxides of tellurium on the CZT surface and thus acts as a good passivating agent. In this study we will present results on the use of potassium hydroxide (KOH) as an alternative passivating agent. The KOH aqueous solution leaves a more stoichiometric (evaluated from the trends in the surface Cd:Te ratio) and smoother CZT surface. The passivation effects of KOH solution on the surface of the CZT have been characterized by current-voltage measurements for different KOH concentrations and etching times for both parallel strip electrodes as well as a metal-semiconductor-metal configuration. The surface chemical composition and its morphology were studied by scanning x-ray photoelectron spectroscopy and atomic force microscopy. The comparison and demonstration of improvements in the spectral resolution of the CZT detectors (based on ²⁴¹Am spectra) with and without the KOH treatment are presented.     

基于单脉冲雷达和差通道多普勒估计的前视成像

单脉冲测角技术用于扫描雷达前视成像可有效提高图像的清晰度,但单个脉冲对同分辨单元多目标测角时会发生角闪烁现象,造成图像模糊.该文提出了一种基于单脉冲雷达和差通道多普勒估计的前视成像算法,利用目标和平台之间相对运动引起的多普勒梯度差异实现同分辨单元内不同方向目标的分离,然后在多普勒域采用和差比幅测角(SDAC)技术测量目...     

Templated growth of cadmium zinc telluride (CZT) nanowires using pulsed-potentials in hot non-aqueous solution

A single step non-aqueous electrodeposition of cadmium zinc telluride (CZT) nanowires on nanoporous TiO₂ substrate was investigated under pulsed-potential conditions. Propylene carbonate was used as the non-aqueous medium. Cyclic voltammogram studies were carried out to understand the growth mechanism of CZT. EDAX and XRD measurements indicated formation of a compound semiconductor with a stoichiometry of Cd_1−xZn_xTe, where x varied between 0.04 and 0.2. Variation of the pulsed-cathodic potentials could modulate the composition of the CZT. More negative cathodic potentials resulted in increased Zn content. The nanowires showed an electronic band gap of about 1.6 eV. Mott-Schottky analyses indicated p-type semiconductor properties of both as-deposited and annealed CZT materials. Increase in Zn content increased the charge carrier density. Annealing of the deposits resulted in lower charge carrier densities, in the order of 10¹⁵ cm⁻³.     

用于CZT探测器信号读出的低噪声电荷灵敏前放A250

本文测量和分析了电荷灵敏前放A250的电子学噪声对CZT探测器能谱展宽的影响.在成形时间下1 μs下A250的零电容噪声为104.8 e,噪声电容斜率为4.18 e/pF.测得241Am 59.5 kev全能峰能量分辨率为4.08%.     

基于不同方法的飞机舱音背景声频谱特征的获取与分析

由于飞机事故的舱音样本不宜对外公布、同一机型的异常舱音背景声也不易在飞行过程中测录到,且基于舱音译码辨听和音频分析的传统方法难以准确获得舱音背景声的频谱特征。因此,获取、检验和比较已获舱音背景声的频谱特征的正确性十分必要。为解决此问题,以测录到的飞机超速音频警告声为研究对象,首先基于小波变换的多尺度分析获取该舱音背景声的频谱特征,然后提出基于线性调频Z变换方法和相关分析方法对该警告声的主要频谱计算比较。结果及应用表明：小波变换、线性调频Z变换（CZT）和相关分析三种不同理论方法的尝试为调查分析飞机事故原因提供了可供比较的、有效的新途径。