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

The Electroreflectance spectra of a GaAs/Al0.3Ga0.7As asymmetric doubl e quantum well have been studied from 30 K to room temperature. The ex perimental spectra consist of various excitonic transition features of the quantum well system above the GaAs band edge, and an inter-band t ransition at the Al0.3Ga0.7As band gap. The first and the second elect ronic subband in the wide well are partially filled by the ionized ele ctrons from Si delta-doping centers in the Al0.3Ga0.7As barriers. The corresponding optical transitions are weak and broadened in the optica l spectra. The strongest spectra feature is due to a resonance between the narrow well and wide well subbands. The modulated reflectance sig nal, Delta R/R, is enhanced thermally by the wide well and narrow well subband resonance. The observed optical transition energies agree wit h the calculated subband energies obtained from the envelope wave func tion model.