  Nanoscale devices are being extensively studied for their tunable electronic
and optical properties, but the influence of impurities and defects is
amplified at these length scales and can lead to poorly understood variations
in characteristics of semiconducting materials. By performing a large ensemble
of photoconductivity measurements in nanogaps bridged by core-shell CdSe/ZnS
semiconductor nanocrystals, we discover optoelectronic methods for affecting
solid-state charge trap populations. We introduce a model that unifies previous
work and transforms the problem of irreproducibility in nanocrystal electronic
properties into a reproducible and robust photocurrent response due to trap
state manipulation. Because traps dominate many physical processes, these
findings may lead to improved performance and device tunability for various
nanoscale applications through the control and optimization of impurities and
defects.
