OPTICAL INVESTIGATION OF SUPERLATTICE ORBITS AND IMPURITY STATES IN INGAAS GAAS/

We have measured optically-detected-cyclotron-resonance on In0.05Ga0.9 5As/GaAs superlattices with large magnetic fields applied both paralle l (Faraday) and perpendicular (Voigt) to the growth direction. Cyclotr on resonance in the Voigt geometry reveals a band structure in the gro wth direction. A semi-classical quantization of the Kronig-Penney disp ersion gives good agreement with the data, providing that the cyclotro n radius is larger than the superlattice period. We observe 1s-2p+ tra nsitions from residual impurities which lie predominantly in the barri er regions. The impurity transition has a remarkable behaviour in the Voigt geometry, moving from the bulk 1s-2p+ field to close to the bulk free electron field as the barrier thickness increases, and is exactl y mid-way between these two limits when the cyclotron radius equals th e barrier thickness.