Mean free drift length of holes in radiation damaged germanium detectors

For radiation damaged HPGe detectors, the mean free drift length of holes λ_h is a useful parameter to characterize the defect structures in the germanium crystal. λ_h depends on three parameters: temperature, electrical field strength, and internal hole current. Multiple measurements with different sets of parameters were carried out to study the functional dependence of λ_h on these parameters. Our data reveal that λ _h follows a square root function of the hole current. In respect to the magnitude of the electrical field E, λ_h possesses two components: one linear in E and the other rising as E^3/2. These dependencies of λ_h on hole current and temperature favor the defect model of Disordered Regions over Isolated Defects, while the dependence of λ_h on electric field strength is beyond these simplistic defect models