Valence-band ordering in ZnO

The emission and reflection spectra of ZnO have been investigated in the intrinsic region and the data have been interpreted in terms of the wurtzite crystal band structure. Free-exciton emission is observed for the first time. Both the ${\ensuremath{\Gamma}}_{5}$ and ${\ensuremath{\Gamma}}_{6}$ state excitons associated with top valence band have been identified. This identification has established the valence-band symmetry ordering in ZnO.