MAGNETOOPTICAL PROPERTIES IN ULTRATHIN INAS-GAAS QUANTUM-WELLS

We determined exciton binding energies in monolayer InAs-GaAs quantum wells by studying photoluminescence excitation spectra in a magnetic field up to 8 T. The effective-mass approximation was used to caluclate the energy levels and determine the excitonic effects associated with Landau-level transitions and the exciton binding energy, which was also determined by extrapolation of higher-lying Landau-level transition energies to zero field. Both procedures lead to heavy-hole-exciton binding energies of the order of 10 meV, i.e., an enhancement of nearly 300% over bulk GaAs. From the diamagnetic shift of the exciton ground state, an estimate of the light-hole-exciton binding energy is made. In-plane effective mass reversal between heavy-hole- and light-hole-exciton states of submonolayer InAs was also observed. Furthermore, electron (exciton)-phonon coupling was also observed by level anticrossing, involving longitudinal as well as local vibrational phonon modes in ultrathin InAs.