  We report on the transport properties of a high mobility two-dimensional hole
system (2DHS) confined in GaAs/AlGaAs quantum wells grown molecular-beam
epitaxy on the (100) surface of GaAs. The quantum wells are modulation-doped
with carbon utilizing a novel resistive filament source. At T=0.3K and carrier
density p=1x10^11cm^-2, a mobility of 10^6cm^2/Vs is achieved. At fixed carrier
density p=10^11cm^-2, the mobility is found to be a non-monotonic function of
the quantum well width. The mobility peaks at 10^6cm^2/Vs for a 15nm well and
is reduced for both smaller and larger well widths for these (100) samples. The
mobility anisotropy is found to be small. Mobility along (0\bar11) is
approximately 20% higher than along the (011) direction. In addition, the low
temperature carrier density is found to have low sensitivity to light. The hole
density increases by only ~10% after exposure to red light at T=4.2K. In
structures designed for a lower carrier density of 3.6x10^10cm^-2, a mobility
of 800,000cm^2/Vs is achieved at T=15mK.
