  In many semiconductors, compensating defects set doping limits, decrease
carrier mobility, and reduce minority carrier lifetime thus limiting their
utility in devices. Native defects are responsible in many cases, but extrinsic
dopants may also act as their own compensation when occupying an alternate
lattice site. Suppressing the concentrations of compensating defects during
processing close to thermal equilibrium is difficult because formation
enthalpies are lowered as the Fermi level moves towards the majority band edge.
Excess carriers, introduced for example by photogeneration, modify the
formation enthalpy of semiconductor defects and thus can be harnessed during
crystal growth or annealing to suppress such defect populations. Herein we
develop a rigorous and general model for defect formation in the presence of
steady-state excess carrier concentrations by combining the standard
quasi-chemical formalism with a detailed-balance description that is applicable
for any defect state in the bandgap. Considering the quasi-Fermi levels as
chemical potentials, we demonstrate that increasing the minority carrier
concentration increases the formation enthalpy for typical compensating
centers, thus suppressing their formation. This effect is illustrated for the
specific example of native GaSb antisite acceptors in nominally un-doped and
extrinsically n-type doped GaSb. The model also predicts reductions in the
concentration of ionized scattering centers as well as increased mobility.
While our treatment is generalized for excess carrier injection or generation
in semiconductors by any means, we provide a set of guidelines for applying the
concept in photoassisted physical vapor deposition.
