Observation of Landau levels and excitons at room temperature in In0.53Ga0.47As/InP quantum wells

We report on magneto-optical Kerr-ellipticity measurements with different In0.53Ga0.47As/InP multiquantum-wells at room temperature. These samples are grown with nominally the same sample parameters, except for the barrier thickness, which for one sample is small enough for a coupling between the quantum wells. The spectral range covered the quantum-well interband transitions of the electron-heavy-hole ground states. The magneto-optical spectra show a number of oscillations, whose spectral position depends on the magnetic-field strength. For model calculations, Lorentzian line shapes for the off-diagonal element of the dielectric tensor have been used, Magneto-optical interference effects are carefully discussed. For small magnetic fields, the shift of the ground state shows a diamagnetic behavior. For the coupled quantum well a transition into the high-field regime can be seen at B approximate to 9 T. Due to the higher exciton energy for the uncoupled system, high-field behavior occurs only at fields beyond the range of the present experiments. Model calculations allow us to estimate from the shift of the ground state (1s), the exciton binding energy and the dimensionality of the system. According to these calculations the uncoupled sample shows a more 2D-like (where 2D is two-dimensional) behavior, while the coupled system is more 3D like. The higher levels, however, are typical for Landau splitting. For these the excitonic effect is negligible compared to the Landau shift. In our experiments, we were able to trace the oscillations up to 200 meV above the band gap of unstrained In0.53Ga0.47As bulk material. This allows us to determine the energy dependence of the reduced effective mass at room temperature. Using the three-band Kane model for the calculation of the electron effective mass, we find that the hole effective mass in In0.53Ga0.47As quantum wells is significantly lower than in bulk material.