Band alignment and directional stability in abrupt and polar-compensated Si/ZnS interface calculations

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.