Effect of interface states on capacitance-voltage characteristics of CdZnTe crystals after surface oxidation

Abstract

The interface states of TeO₂/CdZnTe affects the capacitance voltage characteristics of metal oxide semiconductor (MIS) structured CdZnTe devices. Based on numerical simulations, the interface states exhibit a capacitance hump in the depletion region of the CV curve, which is influenced by substrate doping concentration, frequency, interface state density, and energy level position. According to microstructure and component analysis by high resolution transmission electron microscope and energy dispersive spectroscopy (HRTEM-EDS), MIS-CdZnTe devices with TeO₂ passivation layer of 142–173 nm and limited oxygen diffusion region as interface layers were prepared by NH₄F/H₂O₂ passivation and CMP/NaClO oxidation, respectively, and then used for experimental capacitance characteristic measurement. The results show that the hump capacitance of MIS-CdZnTe prepared by passivation gradually decreases with increasing frequency, consistent with the simulation results, but presents relatively gentle due to the actual interface states with multiple energy levels. Moreover, the influence mechanism of interface traps on CV curve is analyzed using band plots. In addition, the interface state density of MIS-CdZnTe structure is calculated using conductance method, which indicates that the interface state density of MIS- CdZnTe structure prepared by CMP/NaClO method is less than 1/3 that of passivation method (2.11 × 10¹⁰ cm⁻² eV⁻¹), presenting no obvious hump capacitance was observed in its CV curves at low frequencies. Therefore, passivation forms an uneven thickness oxide interface layer between CdZnTe and TeO₂, resulting in a higher density of interface states. While CMP/NaClO treatment forms a limited oxygen diffusion zone and achieves a smooth and dense interface, which can reduce the interface recombination rate, leading to a smaller leakage current (0.067 nA/mm² @ 100 V) for MIS-CdZnTe device, and improving spectral performance of the energy resolution from 11.4 % to 7.7 %.