Surface trapping and detector degradation in Ge bolometers for the EDELWEISS Dark Matter search: experiment and simulation

Surface charging effects are investigated in a germanium ionization-heat detector operated at cryogenic temperatures. Under properly defined biasing conditions, carriers of one type only (either electrons or holes) are driven in a controlled manner into the free surfaces of the detector where they become trapped. Computer simulations allow to determine the surface densities of trapped carriers, and to reconstruct the scatter plot of γ-events in the degraded state. They allow one in particular to define several event populations with respect to detector degradation, attributed to different areas of energy deposition.