Xiaolong Song a, Xiaoyan Liang a, Jiahua Min a, Jijun Zhang a, Shize Li a, Panhui Qiu a, Chengjie Feng a, Chen Xie a, Lingen Dai a, Jun Chen a, Yue Shen a, Linjun Wang b
a School of Materials Science and Engineering, Shanghai University, Shanghai, 200444, China
b Zhejiang Institute of Advanced Materials, SHU, Jiashan, 314113, China
## Abstract
CdZnTe room temperature nuclear radiation detectors are widely used in the fields of homeland security, medical imaging and astrophysics. In the Cd1-xZnxTe radiation detector, the purpose of passivation is to reduce dark current and improve stability. In this study, CdZnTe etched by bromine-methanol (BM) was treated with standard H2O2 and NH4F passivation process. With the help of TEM and EDS measurement results, the thickness of the passivation layer ranges from 126 nm to 183 nm, and X-ray photoelectron spectroscopy (XPS) measurement results show that the TeO2 fraction can be increased on the passivated surface. The dispersion phenomenon on the capacitance-voltage and conductance-voltage curves indicates the existence of carrier trap states in the area near the interface. In order to determine the size of the trap state under this passivation method, an equivalent circuit model was constructed using the calculation method of electrical conductivity. Based on this model, when the voltage increases from 0 V to 1.4 V, the value of the trap state density obtained changes in between 1.07 × 1010 eV−1cm−2 and 5.85 × 1010 eV−1cm−2.
## Introduction
CdZnTe crystal has high atomic number, large forbidden bandwidth and high resistivity [1,2], and is an important material for the preparation of room temperature X-ray and γ-ray detectors [[3], [4], [5]].CdZnTe detectors are widely used in nuclear safety, environmental protection, medical imaging and astrophysics [6,7]. However, the surface characteristics of the crystal have a significant impact on the performance of the radiation detector, and the surface trap state is mainly caused by the dangling bonds on the crystal surface. They can change the periodic potential field on the crystal surface, causing the leakage current on the crystal surface to increase [8,9], and reduce the energy resolution of the detector [10,11]. At present, mechanical polishing, chemical etching and passivation are mainly used to reduce the trap state of the crystal surface [[12], [13], [14], [15]], thereby reducing leakage current and improving the stability of the detector [16,17]. In order to reduce leakage current and improve surface stability, various passivation methods have been proposed [12,18,19]. These methods have been proven to reduce the overall leakage current and improve the energy resolution of the detector. According to reports, NH4F solution can convert Te to TeO2 and form a stable TeO2 layer on the surface of CdZnTe wafers to reduce surface leakage current [20]. For CdZnTe detectors, previous works have mainly investigated the passivation layer from the perspective of dark (leakage) currents as a way to evaluate the effect of the passivation layer on the electrical properties of the detector [16,21]. In fact, the presence of an interfacial state between the TeO2 insulating layer and the CdZnTe semiconductor can also have an important effect on the device.
The study of interfacial states in metal oxide semiconductor structures has been of great interest in recent years. For example, Kun Peng et al. investigated the effect and origin of interfacial states between monolayer MoS2 and HfO2 high-k gate dielectrics [22]. However, no reports on the interfacial states present between CdZnTe and passivation layers have been seen so far [12,23,24].
In this work, we introduce interfacial states into the study of CdZnTe passivation layers. The main objective of the study is to calculate the density of trap states near the passivation region on the surface of CdZnTe crystals using the conductivity method, which is used to evaluate the interfacial condition of the crystals after passivation and to provide a basis for optimizing the crystal interfacial quality in the subsequent passivation work.
CdZnTe Association (CdZnTe.com)
https://www.cdznte.com/thesis/study-on-the-density-of-trap-states-between-cdznte-and-passivation-layer-based-on-mis-structure.html