  Understanding the interaction between dopants and semiconductor-oxide
interfaces is an increasingly important concern in the drive to further
miniaturize modern transistors. To this end, using a combination of
first-principles density-functional theory and a continuous random network
Monte Carlo method, we investigate electrically active arsenic donors at the
interface between silicon and its oxide. Using a realistic model of the
disordered interface, we find that a small percentage (on the order of ~10%) of
the atomic sites in the first few monolayers on the silicon side of the
interface are energetically favourable for segregation, and that this is
controlled by the local bonding and local strain of the defect centre. We also
find that there is a long-range quantum confinement effect due to the
interface, which results in an energy barrier for dopant segregation, but that
this barrier is small in comparison to the effect of the local environment.
Finally, we consider the extent to which the energetics of segregation can be
controlled by the application of strain to the interface.
