High purity germanium crystals operated at cryogenic temperatures (< 20mK) and low electric fi elds (< 1V/cm) are used in the direct dark matter search experiment EDELWEISS-III. The discrimination power of background events and dark matter candidates is strongly in influenced by
the charge collection efficiency in the germanium crystals. For the collection efficiency, surface and bulk trapping, intervalley scattering and the drift velocities of electrons and holes play the main role. As these properties determine the time dependence of the ionization signals, the rise time is a good parameter to study the quality of the detector performance.
In this talk I give an introduction to the EDELWEISS-III experiment and its background rejection methods. I explain how the charge migration can be simulated and compare the simulated time resolved ionization signals with results from measurements with a special EDELWEISS-type detector.
In addition, I show the setup for the time-resolved ionization signal read-out in the EDELWEISS-III experiment and first results from data taking in the underground laboratory of Modane.
