Thermally-Stimulated Current Investigation of Dopant-Related D~(-) and A~(+) Trap Centers in Germanium for Cryogenic Detector Applications

摘要

Thermally-stimulated current measurements provide a sensitive tool to characterize carrier traps in germanium detectors for direct dark matter search. Using this technique at cryogenic temperatures, very shallow traps have been detected with binding energies of a fraction of a meV, associated with the dopant species in the D~(-)(A~(+)) charge states. A positive identification of these traps is achieved through an analysis of the field dependence of the carrier emission rates, which demonstrates a potential well for the trapped carriers in the form of a polarization well in r~(-4), consistent with Lax's model for carrier trapping by a neutral center. The density of these traps is assessed, and implications for the space-charge cancellation procedure in cryogenic Ge detectors are discussed.