Determination of valence band splitting parameters in GaN

Valence band structures and their strain effects in GaN have been investigated by optical spectroscopy for thick GaN films with high optical quality grown by hydride vapor phase epitaxy. Excitons associated with the A, B, and C valence bands are clearly observed in reflectance measurements without modulation techniques. It is found that the exciton energies shift with the film thickness because of the relaxation of the residual strain. From the quantitative analysis of this behavior, we have precisely determined the valence band splitting parameters in GaN as Δ1=10 meV, Δ2=5.5 meV, and Δ3=6.0 meV.