The dispersion of the A-valence-band in GaN has been deduced from the observation of high-index magneto-excitonic states in polarised interband magneto-reflectivity and is found to be strongly non-parabolic with a mass in the range 1.2-1.8 m_{e}. It matches the theory of Kim et al. [Phys. Rev. B 56, 7363 (1997)] extremely well, which also gives a strong k-dependent A-valence-band mass. A strong phonon coupling leads to quenching of the observed transitions at an LO-phonon energy above the band gap and a strong non-parabolicity. The valence band was deduced from subtracting from the reduced dispersion the electron contribution with a model that includes a full treatment of the electron-phonon interaction.
@article{arxiv.cond-mat/0105315,
title = {Free carrier effects in gallium nitride epilayers: the valence band dispersion},
author = {P. A. Shields and R. J. Nicholas and F. M. Peeters and B. Beaumont and P. Gibart},
journal= {arXiv preprint arXiv:cond-mat/0105315},
year = {2009}
}