Influence of the electronic states anisotropy on the band gap pressure coefficient of In_xGa_1-xN alloys

Using the first-principle methods, we investigate the structural and electronic properties of the wurtzite In_xGa_1-xN (0≪x≪1) alloys under hydrostatic pressure. We find that the pressure coefficient decreases with the In concentration and becomes constant when the In concentration is higher than some critical value, which is in agreement with experimental results. Our calculations demonstrate that the axial ratio c/a of In_xGa_1-xN increases with the hydrostatic pressure when x≪0.25, while it decreases when x≫0.25. The densities of p_x and p_y orbitals are higher than that of p_z orbital at the valence band top. This anisotropy induces the pronounced bowing of the pressure coefficient.