Detectors of the cryogenic dark matter search: Charge transport and phonon emission in Ge(100) crystals at 40 mK

The Cryogenic Dark Matter Search (CDMS) measures both the ionized charge and the energy in athermal phonons created by particle interactions in ultrapure germanium and silicon crystals at a temperature of 40 mK. Charge collection potentials must remain at only a few volts, else emitted phonons from drifted carriers will dominate the phonons of the original interaction. At these drift fields, there are practically no thermal phonons and carrier transport is determined by phonon emission. We present results for drift-limited carrier dynamics and rates of phonon emission in < 100 > germanium. As these transport conditions represent an extreme limit, a Monte Carlo technique was used to bypass analytical assumptions commonly used in solving the Boltzmann transport equation. This work will assist us in understanding phenomena found in our detectors.