  Carrier-type reversal to enable the formation of semiconductor p-n junctions
is a prerequisite for many electronic applications. Chalcogenide glasses are
p-type semiconductors and their applications have been limited by the
extraordinary difficulty in obtaining n-type conductivity. The ability to form
chalcogenide glass p-n junctions could improve the performance of phase-change
memory and thermoelectric devices and allow the direct electronic control of
nonlinear optical devices. Previously, carrier-type reversal has been
restricted to the GeCh (Ch=S, Se, Te) family of glasses, with very high Bi or
Pb doping concentrations (5 to 11 at.%) incorporated during high-temperature
glass melting. Here we report the first n-type doping of chalcogenide glasses
by ion implantation of Bi into GeTe and GaLaSO amorphous films, demonstrating
rectification and photocurrent in a Bi-implanted GaLaSO device. The electrical
doping effect of Bi is observed at a 100 times lower concentration than for Bi
melt-doped GeCh glasses.
