Photoreflectance study of GaAsAl0.3Ga0.7As resonant asymmetric double quantum wells with Si δ-doping in side barriers

The electro-optical properties of GaAsAl0.3Ga0.7As resonant asymmetric double quantum wells with Si δ-doping in side barriers have been investigated by photoreflectance spectroscopy from 20 K to room temperature. The modulated reflectance spectra consist of Franz-Keldysh oscillations above the Al0.3Ga0.7As band gap, and various excitonic transition features of the quantum well system above the GaAs band edge. The first and the second excitonic transitions are weak and broadened due to the subband filling effect. The third excitonic transition has the strongest optical response, and we believe this is due to the resonance between the narrow well and the wide well subbands. The enhancement of the modulated reflectance signal, ΔRR, at about 50 K also agrees with the subband resonance model.