Effects of biaxial strain and chemical ordering on the band gap of InGaN

We have performed first-principles calculations to examine the effects of biaxial strain and chemical ordering on the band gap of wurtzite InxGa1−xN in the range 0⩽x⩽0.5. Our results for random unstrained alloys are in good agreement with theoretical estimates and measurements on unstrained zinc-blende alloys, but are in poor agreement with recent measurements on strained wurtzite alloys which display significantly lower band gaps. Biaxial strain is found to have a nonlinear effect on alloy band gaps, increasing them for x<0.25 and decreasing them for x>0.25. However, the overall agreement with measurements on wurtzite alloys remains poor. Chemical ordering along the [0001] direction in strained alloys is found to decrease their band gaps considerably, reducing the discrepancy with measurements. We discuss our results with regard to the current understanding of InGaN alloys.