Space-Charge Manipulation Under Sub-bandgap Illumination in Detector-Grade CdZnTe

The effects of sub-bandgap illumination on the charge transport process and detector performance were experimentally studied in detector-grade CdZnTe. Based on the resulting bulk resistivity and photocurrent response under sub-bandgap illumination, the variation of the deep-level occupation fraction was identified according to a modified Shockley–Read–Hall model. From laser-beam-induced transient current measurements, a decrease of negative space-charge density and consequently flattening of the electric field distribution were found under external sub-bandgap illumination, demonstrating a reduction of the active trap concentration. Furthermore, ²⁴¹Am gamma-ray spectroscopy response measurements confirmed that simultaneous incidence of sub-bandgap light could significantly improve CdZnTe detector energy resolution and charge collection efficiency.