Geant4 modeling of spectral performance and parameter effects in CdZnTe detectors

Cadmium Zinc Telluride (CdZnTe, CZT) detectors are widely used in the field of nuclear radiation detection due to their high intrinsic efficiency and excellent energy resolution. This study systematically investigates the energy spectrum response of planar CdZnTe (CZT) detectors by combining the Monte Carlo simulation tool GEANT4 with the analysis framework based on the Shockley-Ramo theorem and the Hecht equation. GEANT4 accurately simulates the interaction process of γ-rays within the detector and records the energy deposition locations, while the Hecht equation establishes a quantitative relationship between charge carrier transport parameters (such as carrier mobility-lifetime product (μτ), electric field strength, and drift distance) and charge collection efficiency. Using this coupled framework, the effects of key parameters-(μτ), bias voltage, and crystal thickness-on energy resolution and photopeak tailing are explored. The simulation results reveal that, under conditions of high electron collection efficiency, energy resolution is highly sensitive to the ratio of electron to hole μτ ((μτ)_e/(μτ)_h), with smaller ratios yielding improved resolution. Increasing the bias voltage enhances carrier collection and energy resolution, while a thicker detector reduces the contribution of holes to the total induced charge, thereby mitigating tailing and improving energy resolution. This study establishes a theoretical framework for deciphering spectral response mechanisms and guiding performance optimization in CZT detectors.