Fabrication and characterization of p-type Inverted Coaxial Point Contact (ICPC) detectors with a-Ge dual-blocking contacts

Abstract We report the fabrication and characterization of two p-type inverted coaxial point contact (ICPC) high-purity germanium (HPGe) detectors, SAP16 and SAP17, produced from USD-grown crystals with net impurity concentrations of ∼ 3 × 10 10 cm -3 . Both devices employ thin amorphous-germanium (a-Ge) dual-blocking contacts, implemented here for the first time on ICPC detectors, to provide bipolar charge blocking while limiting dead-layer thickness. Electrical tests at 76 K demonstrate stable operation with picoampere-level leakage currents and sub-pF capacitance: SAP17 reached ∼ 4.62 pA at the maximum tested bias (500 V) and operated stably at 400 V with C ≃ 0.503 pF. Meanwhile , SAP16 achieved superior spectroscopic performance, with energy resolutions of 2.42% at 59.5 keV and 0.36% at 662 keV. Gamma-ray spectroscopy with 241 Am and 137 Cs shows that modest geometric differences lead to measurable changes in depletion behavior and charge-collection uniformity, consistent with electrostatic modeling. Angular-response measurements further reveal pronounced directional sensitivity at 59.5 keV, whereas the 662 keV response is essentially isotropic over the measured range. These results validate thin a-Ge dual-blocking contacts for ICPC HPGe detectors and highlight geometry-driven trade-offs among leakage current, depletion, and energy resolution relevant to low-background and low-threshold applications.