2025/11/25 by Budhathoki, Narayan, Mei, Dongming, Bhattarai, Sanjay +5
#Applied Physics (physics.app-ph) #FOS: Physical sciences
paper · doi:10.48550/arxiv.2511.20842
Understanding how charge-carrier mobility evolves as high-purity germanium (HPGe) is thinned from bulk to micrometer scale is essential for optimizing advanced radiation detectors, thin-body Ge electronics, and emerging quantum devices. We report, to our knowledge, the first systematic thickness-dependent mobility study on bulk-grown, detector-grade HPGe, performing Hall-effect measurements on n- and p-type samples thinned from 2.7~mm down to 7~μm at room temperature. The mobility follows an extended-exponential dependence μ(t) = μ0 [ 1 - exp( - (t/τ)β ) ] with characteristic electrostatic lengths τ= 6--50~μm. Comparison with boundary-scattering and depletion-based models shows that mobility degradation is dominated not by Fuchs--Sondheimer surface scattering but by electrostatic depletion that reduces the effective conducting channel thickness. Across all samples, the hierarchy λD < τ\lesssim W0 identifies long-range screening and near-surface electric fields as the primary mechanisms governing the mobility crossover. This connection provides a simple device-level design rule: maintaining t \gtrsim 3τ preserves most of the bulk mobility, while thinner devices enter a depletion-controlled regime with sharply reduced transport. The extracted parameters thus supply quantitative benchmarks for mobility engineering in ultrathin HPGe and a predictive framework for Ge-on-insulator structures, fully depleted channels, and future Ge-based quantum and electronic technologies.