  The doping of semiconductor materials is a fundamental part of modern
technology, but the classical approaches have in many cases reached their
limits both in regard to achievable charge carrier density, as well as
mobility. Modulation doping, a mechanism that exploits the energy band
alignment at an interface between two materials to induce free charge carriers
in one of them, has been shown to circumvent the mobility restriction. Due to
an alignment of doping limits by intrinsic defects, however, the carrier
density limit cannot be lifted using this approach. Here we present a novel
doping strategy using defects in a wide band gap material to dope the surface
of a second semiconductor layer of dissimilar nature. We show that by
depositing an insulator on a semiconductor material, the conductivity of the
layer stack can be increased by seven orders of magnitude, without the
necessity of high temperature processes or epitaxial growth. This approach has
the potential to circumvent limits to both carrier mobility and density,
opening up new possibilities in semiconductor device fabrication, particularly
for the emerging field of oxide thin film electronics.
