  We implement metallic layers of Si-doped (110) GaAs as modulation doping in
high mobility p-type heterostructures, changing to p-growth conditions for the
doping layer alone. The strongly auto-compensated doping is first characterized
in bulk samples, identifying the metal-insulator transition density and
confirming classic hopping conduction in the insulating regime. To overcome the
poor morphology inherent to Si p-type (110) growth, heterostructures are
fabricated with only the modulation doping layer grown under p-type conditions.
Such heterostructures show a hole mobility of 1.75x10^2 cm^2/Vs at density
p=2.4x10^11 cm^-2. We identify the zero field spin-splitting characteristic of
p-type heterostructures, but observe a remarkably isotropic mobility and a
persistent photoconductivity unusual for p-heterojunctions grown using other
doping techniques. This new modulated growth technique is particularly relevant
for p-type cleaved-edge overgrowth and for III-V growth chambers where Si is
the only dopant.
