Effect of biaxial strain on the band gap of wurtzite Al _x Ga _1-x N

First-principles calculations are applied to investigate the effect of biaxial strain on the band gap of wurtzite Al _x Ga _1-x N. The band gap and band gap bowing parameter increase with compressive strain and decrease with tensile strain. The strain-induced changes in the band gap of Al _x Ga _1-x N are linear in the strain range of about -1% to 1% while the linearity is invalid out of the range. The linear coefficient B(x), characterizing the relationship between the band gap and the biaxial stress, with a quadratic form is obtained. The value of the band gap bowing parameter decreases from 1.0 eV for -2% strain to 0.91 eV for unstrained and to 0.67 eV for 2% strain.