Effect of in-plane biaxial strains on the band structure of wurtzite GaN

The effect of strain on wurtzite GaN is studied theoretically using an sp³d⁵-sp³ empirical tight-binding model. The model incorporates all nearest-neighbor and some second-nearest-neighbor interactions within the two-center approximation. The second-nearest-neighbor interactions excluded are the cation-cation interactions involving the Ga $3d$ orbital. Strain is included by scaling the two-center integrals appropriately. Thus the strain is modeled without invoking deformation potential theory, obviating the need for any additional parameters. The present model can accommodate any arbitrary strain orientation. The band structure has been calculated for in-plane biaxial strain. It is found that the band gap remains direct for in-plane biaxial strains ranging between ±5%. Furthermore, the valence-band edge is of a different symmetry for tensile and compressive strains. The total density of states calculated via a fundamental numerical scheme is given for unstrained and strained GaN.