SUBBAND FILLING AND RESONANCE IN A GAAS/AL0.3GA0.7AS ASYMMETRIC DOUBLE-QUANTUM-WELL

The Electroreflectance spectra of a GaAs/Al0.3Ga0.7As asymmetric double quantum well have been studied from 30 K to room temperature. The experimental spectra consist of various excitonic transition features of the quantum well system above the GaAs band edge, and an inter-band transition at the Al0.3Ga0.7As band gap. The first and the second electronic subband in the wide well are partially filled by the ionized electrons from Si delta-doping centers in the Al0.3Ga0.7As barriers. The corresponding optical transitions are weak and broadened in the optical spectra. The strongest spectra feature is due to a resonance between the narrow well and wide well subbands. The modulated reflectance signal, Delta R/R, is enhanced thermally by the wide well and narrow well subband resonance. The observed optical transition energies agree with the calculated subband energies obtained from the envelope wave function model.