Magneto-reflectivity of gallium nitride epilayers

We have used interband magneto-reflectivity to study the band parameters of wurtzite GaN epilayers grown on sapphire. Using magnetic fields up to 57 T , we have observed a series of up to ten magneto-excitonic transitions for the first time. The levels can be fitted with two intersecting magneto-exci tonic fans coming from the A and B valence band edges with reduced masses o f (0.195 +/- 0.01) m(0) and (0.180 +/- 0.003) m(0) respectively. The field dependence of the A-exciton 1s and 2p states gives a reduced mass of (0.180 +/- 0.005) m(0), and (0.193 +/- 0.005) m(0) is found with the B-exciton 1s state. The B exciton shows a clear spin splitting at 57 T, whereas no spli tting of the A exciton is observed.