Temperature-Dependent Drift Mobility in USD-Grown HPGe for Ultra-Low-Threshold Detectors

We report a systematic investigation of the drift-mobility of USD-grown high-purity germanium (HPGe) between 2–300 K, measured via the four-probe techniques. Self-consistent analyses of the temperature (T) dependence of the longitudinal resistivity (ρ(T)) and Hall coefficient (R_H(T)) distinguish a phonon-limited regime above ∼50 K from ionized-impurity scattering and carrier freeze-out below ∼10 K, yielding temperature-dependent mobility for both electrons (μ_e(T)) and holes (μ_h(T)). The resulting μ_e(T) and μ_h(T) curves provide quantitative inputs—mobility scaling, freeze-out onsets, and impurity-limited floors—needed to set bias fields, geometry, and operating temperatures in next-generation HPGe devices. In particular, the data calibrates operating windows for Germanium Internal Charge Amplification (GeICA), where high fields exploit impact ionization to enhance charge collection and push energy thresholds to the sub-eV scale. Together, these measurements establish a materials-anchored foundation for ultra-low-threshold rare-event and quantum-sensing detectors based on modern HPGe.