  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, non-polar optical
phonons, and acoustic phonons are included. Using a Schrodinger/Poisson solver,
the heavy hole, light hole, and split-off bands are treated separately. To
compare the calculations with experimental data, Hall-effect structures were
fabricated and measured at temperatures ranging from 25 to 700 K, with hole
sheet densities ranging from 2 to 6$\times10^{12}\;\text{cm}^{-2}$ and typical
mobilities measured from 60 to 100 cm$^{2}$/(V$\cdot$s) at room temperature.
Existing data from literature was also used, which spans sheet densities above
1$\times10^{13}\;\text{cm}^{-2}$. 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 suggests that long-range potential fluctuations exist at the
diamond surface, and are particularly enhanced at lower sheet densities. Thus,
we propose a second type of surface impurity scattering which is caused by
disorder related to the C-H dipoles.
