Observation of Time-Dependent Impact Ionization in a Large-Size Ge Detector Made from a Crystal Grown at USD

An experiment to understand the charge transport in a SuperCDMS-style Ge detector made from a crystal grown at USD was performed at the University of Minnesota. An Am-241 movable source was used to characterize the 59.54 keV peak in the energy spectra from each channel. This study will help to understand the charge transport, charge trapping, and charge generation processes inside the detector at a cryogenic temperature. We investigated the time-dependent impact ionization induced by holes at mK temperature and studied the charge breakdown. We observed time-dependent impact ionization, which is due to the creation of overcharged states in the detector. The binding energy of the overcharged states was determined using the data taken at different temperatures.