Band gap tuning in GaN through equibiaxial in-plane strains

Structural transformations and the relative variation in the band gap energy $(ΔEg)$ of (0001) gallium nitride (GaN) films as a function of equibiaxial in-plane strains are studied by density functional theory. For relatively small compressive misfits (−6%–0%), the band gap is estimated to be around its strain-free value, while for small tensile strains (0%–6%), it decreases by approximately 45%. In addition, at large tensile strains $(>14.5%)$⁠, our calculations indicate that GaN may undergo a structural phase transition from wurtzite to a graphitelike semimetallic phase.