Band gap bowings and anomalous pressure effects in III-V nitride alloys: Role of In-segregation

Using ab initio calculations a comparison between InxGa1-xN, InxAl1-xN and GaxAl1-xN is performed to examine the role of indium in nitride alloys. The band gap, E-g, as well as its pressure coefficient, dE(g)/dp, are studied as functions of chemical composition, x. Following theoretical and experimental suggestions about the crucial role of In-segregation in InxGa(1-x)N and InxAl1-xN, different arrangements of In atoms, uniform and clustered are considered. The presence of In and its clustering introduces a significant reduction of both E-g and dE(g)/dp as well as strong bowings. These effects are most pronounced in InxAl1-xN, (with x = 0.25) and depend strongly on clustering geometry. It is shown that the In-N bonds are shortened when more than one In-cation is bound to the one nitrogen anion. The stong hybridization of wave functions (IN-p,d-states and N-p-states) at the top of the valence band is responsible for the enhancements of bowings in the case of clustered distribution of indium atoms. (C) 2011 WILEY-VCH Verlag Gmbh & Co. KGaA, Weinheim