Characterizing the Temperature Dependence of Charge Trapping Effects in HPGe Detectors for use in Neutrinoless Double-Beta Decay Experiments

An effect which can have a significant impact on charge collection and signal readout in semiconductor detectors is `charge trapping,' whereby defects in the crystal (e.g. dopant impurities or dislocations in the lattice) cause localized electronic states in the band-gap which can cause charge carriers to weakly bind to them, temporarily trapping them until they are released back into the conduction band. The characteristic trap time, τ<sub>ct</sub>, depends on the effective `depth' of the trap and the temperature of the system; at low temperatures, these release times can become long compared to the signal collection time, leading to degraded signal amplitude and an inability to reconstruct the `true' energy of the initial event.

For germanium-based 0νββ experiments such as LEGEND (the Large Germanium Experiment for Neutrinoless double-beta Decay), understanding the nature and origin of these trapping sites in HPGe detectors is critical, as they require the ability to reconstruct the energy deposition and the topology of particle interactions in their detectors to an extreme degree. This talk will present an overview of an experimental test stand being developed at Los Alamos National Laboratory to identify the nature of the charge trapping sites in the HPGe crystals using temperature-dependent measurements of the defect-specific characteristic release times τ_ct.