Tunable optoelectronic and ferroelectric properties in Sc-based III-nitrides

Sc-based III-nitride alloys were studied using density functional theory with special quasi-random structure methodology. ScxAl1-xN and ScxGa1-xN alloys are found to be stable in hexagonal phases up to x approximate to 0.56 and x approximate to 0.66, respectively, above which rock-salt structures are more stable. Epitaxial strain stabilization can prevent spinodal decomposition up to x approximate to 0.4 (ScxAl1-xN on AlN or GaN) and x = 0.27 (ScxGa1-xN on GaN). The increase in Sc content expands the in-plane lattice parameter of ScxAl1-xN and ScxGa1-xN alloys, leads to composition-and strain-tunable band gaps and polarization, and ultimately introduces ferroelectric functionality in ScxGa1-xN at x approximate to 0.625. A modified Becke-Johnson exchange-correlation potential was applied to study the electronic structures, which yielded band gaps comparable to those from hybrid functional calculations, yet in a much shorter computational time. The alloys were found to retain wide band gaps, which stay direct up to x = 0.25 (ScxAl1-xN ) and x = 0.5 (ScxGa1-xN). The band gaps decrease with increasing x for ScxAl1-xN , in which the Sc-3d states dominate at the conduction band minimum and lead to flat electron dispersion at the C point. Conversely, the band gaps increase with increasing x for ScxGa1-xN (up to x 0.5), in which Sc-3d states do not contribute to the conduction band minimum at the Gamma point. (C) 2013 AIP Publishing LLC.