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 less than or equal tox less than or equal to0.5. 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. (C) 2001 American Institute of Physics.