Large and composition-dependent band gap bowing in InxGa1−xN alloys

We present theoretical and experimental results for the band gap of InxGa1−xN alloys, showing significantly larger bowing than has been commonly assumed. We highlight the importance of properly including strain in the experimental analysis. Using X-ray diffraction (XRD) and Rutherford backscattering spectrometry the layers in our study were determined to be pseudomorphically strained. The In content determined by XRD depends strongly on the assumptions made about the strain in the InGaN layers. Strain also affects the band structure and hence the transition energies measured by optical-transmission spectroscopy. An analysis of the experimental results produces a bowing parameter b≈3.8 eV at x=0.1. First-principles calculations, based on pseudopotential–density–functional theory, produce values of the bowing parameter in agreement with the experimental determination, and also indicate a strong dependence of the bowing parameter on composition.