Characterization of large volume HPGe detectors. Part I: Electron and hole mobility parameterization

An analytical model for the hole mobility in a Ge crystal lattice was developed to describe the hole drift anisotropy with experimental velocity values along the crystal axis as parameters. The new model is based on the drifted Maxwellian hole distribution in Ge. It is verified by reproducing experimental longitudinal hole anisotropy data with high accuracy. A comparison between electron and hole mobility shows large differences for the longitudinal and tangential velocity anisotropy as a function of the electrical field orientation with respect to the crystal orientation. The anisotropic mobility causes measurable differences on rise times and pulse shapes which vary with the location where the charge carriers are created in the Ge crystal. These effects are relevant for position determination and γ -ray tracking.