Analysis of mobility-limiting mechanisms of the two-dimensional hole gas on hydrogen-terminated diamond

Abstract

Here, we present an analysis of the mobility-limiting mechanisms of a two-dimensional hole gas on hydrogen-terminated diamond surfaces. The scattering rates of surface impurities, surface roughness, nonpolar optical phonons, and acoustic phonons are included. Using a Schr\"odinger/Poisson solver, the heavy-hole, light-hole, and split-off bands are treated separately. To compare the calculations with experimental data, Hall-effect devices were fabricated and measured at temperatures ranging from 25 to 700 K with hole sheet densities ranging from 2 to $6\ifmmode\times\else\texttimes\fi{}{10}^{12}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ and typical mobilities measured from 60 to $100\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ at room temperature. Existing data from literature were also used, which span sheet densities above $1\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$. Our analysis indicates that, for low sheet densities, surface impurity scattering by charged acceptors and surface roughness are not sufficient to account for the low mobility. Moreover, the experimental data suggest that long-range potential fluctuations exist at the diamond surface and are, particularly, enhanced at lower sheet densities. Thus, a second type of surface impurity scattering is proposed and is presumed to arise by disorder related to the carbon-hydrogen dipoles.