Advancing HPGe Detector Architectures for Rare-Event Physics with USD-Grown Crystals

Rare-event searches (dark matter, CEνNS, neutrinoless double-β decay) require germanium detectors that couple ultralow noise and backgrounds with stable, scalable electrode geometries. Meeting these demands hinges on understanding and controlling contact physics. These include Li-diffused n+ layers, amorphous-Ge/metal p+ stacks, and sidewall passivation, which set leakage, capacitance, charge collection, and long-term stability. We report end-to-end progress at USD toward this goal, emphasizing (i) a hybrid planar device that integrates an in-house Li-diffused n+ backside with sputtered a-Ge/Al p+ signal contacts and a-Ge sidewall passivation, and (ii) the development of a ring-contact (GeRC) architecture employing fully a-Ge contacts to shape weighting fields for low-capacitance readout. Device simulations (depletion, capacitance, weighting fields) inform electrode design and biasing, while I–V/C–V, tagged-source spectroscopy, and narrowband phonon/charge calibrations are used to map contact-dependent response. A central objective is to verify and correlate detector performance with materials quality in USD-grown high-purity Ge crystals, establishing a reproducible path from crystal growth to instrument-grade devices. This program targets robust, scalable HPGe modules with the noise, stability, and field control needed for next-generation rare-event experiments.