  We investigate the effect of basal-plane stacking faults on the structural,
electronic, and polarization properties of wurtzite GaN and ZnO. This
theoretical study is performed within density-functional theory (DFT) using
periodic hexagonal supercells. Both formation energies and band structures are
obtained by means of total-energy calculations. The type-I stacking fault is
observed to have the lowest formation energy, followed by type-II and finally
the extrinsic stacking fault. In order to overcome the inherent shortcoming of
DFT in reproducing band gaps, the generalized-gradient approximation is used in
combination with the modified Becke-Johnson functional. It is shown that all
stacking faults studied maintain a direct gap whose value is lower than that in
the ideal defect-free crystals. The lowering in the band gap allows the
creation of quantum-well regions at wurtzite/zincblende interfaces. In
addition, we provide a consistent set of polarization parameters derived from
the Berry-phase method. We find a trend of decreasing (increasing) spontaneous
polarization and piezoelectric coefficient (polarization charge) in going from
type-I to type-II to extrinsic stacking faults. We compare our results to
experimental and theoretical data available from the literature and explain the
observed trends in terms of the properties of the wurtzite and zincblende
polytypes of both materials.
