Fabrication of Li/In Double-Sided Diffusion Contacts in Planar High-Purity Germanium Detectors and Their Low-Temperature X-Ray Response

Li n+ and In p+ diffusion contacts were fabricated on p-type 12N high-purity germanium (HPGe) single crystals by vacuum evaporation of thin-film sources followed by solid-state thermal diffusion. The effects of diffusion temperature on the near-surface structure, morphology, impurity distribution, and device response were systematically investigated. XRD and Raman analyses show that Li diffusion at 100–300 °C and In diffusion at 600–800 °C preserve the bulk Ge crystal structure, whereas higher diffusion temperatures induce surface roughening, near-surface disordering, and interfacial reactions. SIMS depth profiles combined with diffusion simulations confirm effective inward diffusion of both Li and In, with low-concentration tailing that is consistent with defect-assisted diffusion or interfacial trapping. The sample diffused with Li at 200 °C exhibits the lowest dark current, 8.07 × 10−8 A at −10 V. The final HPGe device with Li/In diffusion contacts shows a stable synchrotron X-ray photoconductive response, and the net response current increases from 4.48 × 10−7 to 1.15 × 10−6 A as the incident photon flux increases. These results demonstrate that low-leakage HPGe diffusion contacts require a balance between diffusion-layer formation and near-surface/interface stability, rather than a simple increase in thermal budget.