Low field excitonic Zeeman splittings in gallium nitride

Reflectivity and Kerr rotation were measured on a GaN layer grown by MOVPE on sapphire substrate. Fine excitonic structures were observed. Energies of A, B, and C free excitons were determined, as well as those of 2s excited states of A and B excitons, thus the exciton binding energies were obtained for A and B excitons, in reasonable agreement with previously reported data. Very small excitonic Zeeman splittings (down to 80 μeV) were determined from the analysis of the Kerr rotation data. The splittings, although different from those obtained at high fields on homoepitaxial GaN layers, can be described using an excitonic model with the same band parameters.