The energy band gap of AlxGa1-xN

Combining experimental measurements with an analysis of sample strain, we have determined the "unstrained" energy band gap, E-g of AlxGa1-xN for 0 less than or equal to x less than or equal to 1. Care was taken to grow films with narrow (00.2) and (10.2) X-ray diffraction rocking curve widths, to insure low residual strain in the samples. This is significant because, even for our high quality AlxGa1-xN thin films, residual strain shifts the fitted band gap bowing parameter significantly. For AlxGa1-xN random alloys on GaN films deposited on sapphire. the strain-corrected band gap dependence on alloy composition is fit well by a bowing, parameter of b = 0.70 +/- 0.05. In contrast. AlxGa1-xN films deposited directly on sapphire had much higher X-ray line-widths and their E-g's are not fit well by one value of the bowing parameter. This suggests that material quality may he a significant reason for the large range of bowing parameters reported in the literature.