We investigate lattice ordering phenomena for the heterovalent ternaries that are based on the wurtzite lattice, under the constraint that the octet rule be preserved. We show that, with the single exception of a highly symmetric twinned structure, all allowed lattice orderings can be described by a pseudospin model corresponding to the two different stackings of ABAB rows of atoms in the basal plane that occur in the P na21 and P mc21 crystal structures. First-principles calculations show that the difference in the energies of formation between these two structures is 13±3 meV/fu (formula unit) for ZnSnN2 and is an order of magnitude larger for ZnGeN2, and that for both materials the P m31 structure, which contains only octet-rule-violating tetrahedra, has a significantly higher energy of formation and a signficantly lower band gap. We predict almost random stacking and wurtzite-like x-ray diffraction spectra in the case of ZnSnN2, consistent with reported measurements. The octet-rule-preserving model of disorder proposed here predicts a band gap that for ZnSnN2 is relatively insensitive to ordering, in contrast to the prevailing model, which invokes the random placement of atoms on the cation sublattice. The violations of the octet rule in the latter model lead to significant narrowing of the band gap. The Raman and photoluminescence spectra of ZnSnN2 are interpreted in light of the ordering model developed here. The observation that ZnGeN2 orders in the P na21 structure under appropriate growth conditions is consistent with the larger difference in the energies of formation of the P na21 and P mc21 structures for this material. The ordering model presented here has important implications for the optical, electronic and lattice properties of all wurtzite-based heterovalent ternaries.

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The II‐IV‐N2 semiconductors constitute a family of heterovalent ternary semiconductors with properties closely related to those of the III‐Nitrides. We here focus on Zn‐IV‐N2 semiconductors with the group IV‐element Si, Ge and Sn. We present results on their electronic band structures obtained with the quasiparticle self‐consistent GW method and the full‐potential linearized muffin‐tin orbital method. The latter is also used to calculate the energies of formation of these compounds from the constituent elements. The lattice dynamical properties were presented earlier in a series of papers and the main properties are briefly reviewed here. We emphasize the trends in the family of materials compared to those of the III‐N and discuss the experimental data for the phonons. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The band offsets between the Zn-IV-N2 nitrides, ZnGeN2 and ZnSnN2, and two other closely lattice matched semiconductors, ZnO and GaN, are calculated using density functional theory calculations including quasiparticle corrections. The interface dependence as well as the role of strain are investigated. A staggered type-II alignment is found between ZnGeN2, GaN and ZnO with ZnO having the lower and ZnGeN2 having the higher valence band maximum. The potential benefits of this alignment for photovoltaic applications is pointed out.