Intrinsic origin of the breakdown of quasi‐cubic approximation in nitride semiconductors

Abstract

AbstractWe investigate the intrinsic origin of the breakdown of the quasi‐cubic approximation in hexagonal GaN (h‐GaN) on the basis of first‐principles calculations. It is found that the breakdown is caused by the third‐nearest‐neighbour interactions as well as deviations from the “ideal wurtzite structure” in the lattice‐constant ratio (c /a) and the internal parameter (u). This means that the breakdown appears even in ideal structures. Furthermore, we investigate large strain effects on the deformation potentials. We find that the potentials of h‐GaN under large biaxial strain are significantly different from those of unstrained material, although no such difference is seen in cubic GaN. It is suggested that the nonlinearity is linked with the internal parameter (u), an additional degree of freedom. These results imply that these effects should be considered in the design of nitride‐based optical devices using strained active layers (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)