Low-resistance Ohmic contacts on n-type Ge enabled by AgSb-induced self-doping

Low-resistance electron injection into lightly doped n-type Ge is hindered by strong Fermi-level pinning and the resulting wide depletion region. Here we demonstrate an implant-free, lithography-compatible route to ohmic contacts on n-Ge (Nd ≈ 3 × 1015 cm 3) based on AgSb (99:1) alloy metallization and rapid thermal annealing. Circular transfer length method (CTLM) patterns reveal a reproducible transition from rectifying to ohmic behavior above ~400 ◦C, consistent with Sb out-diffusion from the metal and near-interface donor activation that narrows the barrier and promotes tunneling-assisted transport. The specific contact resistivity reaches a minimum of ρc = (1.67 ± 0.05) × 10 3 Ω⋅cm2 at 420 ◦C, with LT ≈ 76 μm and Rs ≈ 29 Ω/sq. The non-monotonic temperature dependence indicates an optimal process window where dopant activation dominates over high- temperature interfacial degradation. This self-doping contact scheme provides a scalable pathway to low- background-doped Ge platforms relevant to Ge-based electronics, integrated photodetectors and quantum de- vices, while remaining compatible with standard microfabrication methodologies.