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Abstract:

The new technique of Far InfraRed Modulated PhotoLuminescence (FIRM-PL) has been used to study the properties of a high mobility 2-D electron gas in a series of GaAs/AlGaAs heterojunctions and quantum wells. When the occupancy of the lowest Landau level is between 1 and 2 very large transfers of PL intensity are observed at the cyclotron resonance condition. The FL intensity is transferred from the E-0 line to F-1 corresponding to emission from the first two quantised electric subbands. A study of the power dependence of this signal allows us to deduce that the relative recombination efficiencies of the two lines are around 5 orders of magnitude different in such structures. This difference leads to a very high sensitivity for this technique for the observation of internal excitations within the electron system. In quantum wells signals are seen for all occupancies due to transfer between PL from higher Landau levels.

Abstract:

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-excitonic fans coming from the A and B valence band edges with reduced masses of (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 splitting of the A exciton is observed.