  We perform a first principles investigation of Si/ZnS interface properties
for the [111], [100], and [110] directions, including single-substitution
polar-compensated interfaces. The asymmetry of general interface directions
poses known challenges for standard methods of calculation: a multiplicity of
interface distinctions, artificial electric fields, and indeterminacy of
orientation stability. By placing each distinct interface in a variety of
supercell environments, we demonstrate that the spread of both band offsets and
interface enthalpies is acceptably small for reasonable cell lengths, removing
the need for corrections involving inappropriate assumptions or computationally
expensive structures. Both the orientation and the ionic character of abrupt
(111) zinc blende interfaces are shown to affect band alignment and interface
enthalpy. We find that the band offsets for the compensated and abrupt (111)
and (100) interfaces lie on a strongly bimodal distribution of total width
greater than 1.2 eV, while the (110) band offset lies near the distribution
midpoint. The midpoint agrees with previous experiments on (100) interfaces,
but only one peak of the distribution agrees with (111) interface experiments,
indicating that the grown macroscopic (111) interfaces had significant
selectivity among the possible microscopic interfaces. The polar-compensated
interfaces are shown to be more stable than the corresponding abrupt interfaces
over most growth conditions.
