Confined 1S excitons, Landau transitions, and cavity mode coupling in GaAs microcavities

The reflection spectra of GaAs microcavities (MC) formed between GaAs/AlxGa1-xAs distributed Bragg reflectors were studied at T = 2 K and under a magnetic field applied perpendicularly to the layers (z direction). Several MC's were studied, whose length L-MC similar to lambda(exc) = 223 nm corresponds to the 1S exciton wavelength of bulk GaAs at T = 2 K {[}E(1S) = 1.515 eV]. The spectra show a large number of sharp lines either within the broad MC-confined photon band, when the MC mode overlaps the continuum absorption, or within the upper Rabi split band when the MC mode is near resonance with the lowest 1S exciton states. The energy and intensity of these sharp lines vary with increasing magnetic field (0 0 that are spatially confined in the lambda(exc)-wide MC, resulting in a quantization of their center of mass motion. (b) Landau transitions (magnetoexcitons) between electron and hole Landau levels with indices ranging up to p = 11. (c) MC-confined photons. The reflection spectra are calculated by constructing transfer matrices that describe light propagation along the z direction (in the MC and in each layer of the distributed Bragg reflectors) and introducing an energy-dependent dielectric function for the GaAs layer, in the form of a Lorentzian oscillator response function for the 1S exciton and for each one of the magnetoexcitons. The 1S exciton center of mass quantization is introduced by including its k(z) dispersion within the dielectric function and using Pekar's additional boundary condition. The calculated spectra fit reasonably well the experimental ones (in both energy and intensity). The fan diagrams show anticrossings between the spatially confined 1S exciton levels and the p greater than or equal to 1 magnetoexcitons, as they are tuned by the magnetic field. These anticrossings are observed experimentally only in the MC mode spectral range, as predicted by the model. Using the same model, the electronic excitations energy dependence on magnetic field is calculated for the lambda(exc)-wide GaAs layer confined between the Al0.3Ga0.7As layers (namely without the distributed Bragg reflectors). No anticrossings are obtained. It is thus concluded that the spatially confined 1S exciton levels and the p greater than or equal to 1 magnetoexcitons are coupled via their interaction with the MC-confined photons. {[}S0163-1829(99)03315-9].