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arXiv · 2609.01522

Fabrication and characterization of lithium-diffused inverted coaxial point-contact HPGe detectors

Anupama Karki·Kunming Dong·Dongming Mei
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Abstract

High-purity germanium (HPGe) detectors with low capacitance, low electronic noise, and stable high-voltage operation are important for high-resolution gamma-ray spectroscopy and rare-event searches. We report the fabrication and characterization of two compact p-type inverted coaxial point-contact (ICPC) HPGe detectors, AK01 and AK02, produced from crystals grown at the University of South Dakota. Both devices use lithium-diffused $n^{+}$ outer contacts together with amorphous-Ge/Al point-contact electrodes. The principal advance is the implementation of this hybrid contact process on two independently fabricated USD-grown ICPC prototypes and the demonstration of stable electrical and spectroscopic operation. Both detectors exhibited picoampere-level leakage currents, operational depletion-voltage ranges of approximately 200--250~V (AK01) and 240--260~V (AK02), and estimated effective plateau capacitances of approximately 0.84 and 0.87~pF, respectively. Measurements with a $^{137}$Cs source yielded archived full-energy-peak FWHM values of 1.71 and 1.62~keV near 662~keV for AK01 and AK02, while AK02 yielded 1.04~keV FWHM at 59.5~keV with $^{241}$Am. Electric-field calculations reproduce the expected ICPC field configuration for the measured detector geometry. A Geant4 model of AK02 is used as a qualitative response study; its 0.8-mm Li-diffused inactive layer is an illustrative model assumption rather than a measured thickness, and its Gaussian broadening is constrained by the experimental resolution. The work therefore establishes the fabrication and operation of compact lithium-diffused ICPC prototypes while identifying quantitative inactive-layer characterization as an important next step.

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Anupama Karki, Kunming Dong, Dongming Mei. 2026-09-01. Fabrication and characterization of lithium-diffused inverted coaxial point-contact HPGe detectors. https://arxiv.org/abs/2609.01522

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