Oscillator strengths for optical band-to-band processes in GaN epilayers

We investigated the evolution; of the relative oscillator strengths of the A, B, and C excitons in alpha-GaN epilayers grown along the [0001] direction an sapphire, 6HSiC, and ZnO substrates by metalorganic vapor phase epitaxy and molecular-beam epitaxy. A universal model was found to account for the observed spectroscopic features regardless of the substrate employ-ed. In addition, we found that, due to the small value of the spin-orbit interaction compared to the stress-induced modifications of the interlevel splitting, C and B Lines may undergo a strain-induced exchange of their oscillator strengths when strain field in the epilayers varies from biaxial tension towards biaxial compression. Moreover, we can account for the strain-induced distribution of radiative recombination rates in high-quality GaN epilayers.