MULTIPLE CYCLOTRON RESONANCES IN GAAS-ALXGA1-XAS QUANTUM-WELLS DETECTED BY RESONANT INELASTIC LIGHT-SCATTERING

Cyclotron resonance excitations in modulation-doped AlxGa1-xAs-GaAs qu antum wells have been investigated by means of resonant inelastic ligh t scattering. Besides the cyclotron resonance excitation (h) over bar omega(C), we observe up to fifteen additional peaks at multiples of (h ) over bar omega(C). The constant energy separation between these reso nances indicates that they are multiple excitations of (h) over bar om ega(C) (and not higher harmonics). These multiple resonances all have nearly the same strength. For an explanation, we propose a cascade mod el, where the photocreated hole in the valence band couples via direct and exchange Coulomb interactions to the Fermi sea. This allows the h ole to relax resonantly by creating cyclotron resonance excitations in the conduction band.