Scattering mechanisms in a high-mobility low-density carbon-doped (100) GaAs two-dimensional hole system

We report on a systematic study of the density dependence of mobility in a low-density carbon-doped (100) GaAs two-dimensional hole system (2DHS). At T=50 mK, a mobility of 2.6 × 106 cm2/Vs at a density p=6.2×1010 cm ^-2 was measured. This is the highest mobility reported for a 2DHS to date. Using a backgated sample geometry, the density dependence of mobility was studied from 2.8 × 1010 cm^-2 to 1 × 1011 cm^-2. The mobility vs density cannot be fit to a power law dependence of the form μ~pα using a single exponent α. Our data indicate a continuous evolution of the power law with α ranging from ~0.7 at high density and increasing to ~1.7 at the lowest densities measured. Calculations specific to our structure indicate a crossover of the dominant scattering mechanism from uniform background impurity scattering at high density to remote ionized impurity scattering at low densities. This is the first observation of a carrier density-induced transition from background impurity dominated to remote dopant dominated transport in a single sample.