Phonon and charge signals from IR and X excitation in the SELENDIS Ge cryogenic detector

The aim of the SELENDIS project within the EDELWEISS collaboration is to observe single $e^- h^+$ pairs in lightweight (3.3 g) cryogenic germanium bolometers with charge and phonon readout at biases up to $\sim 100$ V. These devices are ideal to characterize in detail the mechanism of charge creation and collection in cryogenic germanium detectors. Electron-hole pairs are produced in the bulk of the detector either by the injection of pulsed IR laser or by neutron activation of germanium inducing the K, L and M lines from $^{71}$Ge electron capture decays. Low-energy laser pulses are also used to probe the single $e^- h^+$ pair sensitivity of Ge bolometers. Preliminary results are used to compare these two modes of charge creation, an important step toward a detailed characterization of Ge bolometers for their use in sub-MeV Dark Matter (DM) searches.