Study on the density of trap states between CdZnTe and passivation layer based on MIS structure

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.