Grain boundary limits the performance and application of CdZnTe nuclear radiation detectors. In order to explore the influence of grain boundary in CdZnTe crystals on device performance, the space charge distribution and internal electric field distribution of CdZnTe crystals containing grain boundary were simulated by Silvaco TCAD technique. The simulation results demonstrated that the energy bands at the CdZnTe grain boundary were bent upward in the thermal equilibrium state, forming a back-to-back Schottky barrier. When the applied bias voltage was increased, the overall energy band structure of the Au/CdZnTe/Au tended to tilt from the cathode to the anode and the internal electric field increased with the increase of the applied bias voltage. The dead zone in the crystal gradually decreased and the internal electric field was linearly distributed, which helped to improve the carrier collection efficiency in the device. In addition, the grain boundary defect concentration can regulate the internal electric field distribution of CdZnTe, thus affecting the carrier transport properties.
The effects of temperature on the distribution of space charge and internal electric field in CdZnTe detectors were theoretically simulated by TCAD software. The mechanisms of space charge distribution in CdZnTe detectors at different temperatures and how to manipulate the internal electric field to achieve good detector performance were discussed in this study. The results demonstrated that an uneven internal electric filed distribution was obtained in low temperature. With increasing temperature, the ionized deep levels tended to capture electrons while unionized deep levels to emit electrons. The sub-bandgap light with a wavelength of 850nm and light intensity of 8×10-8W/cm2 were utilized to manipulate space charge distribution by enhancing optical excitation of electrons from the valence band into the ionized deep donor levels. Thus, a flatter internal electric field were achieved, which greatly reduces the probability of carriers being trapped or recombined by defect levels during charge transport processes and then significantly improves the charge collection efficiency of detectors in low temperatures. This simulation results provide a theoretical basis for the application of CdZnTe detectors in astronomical field.
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