PHOTOREFLECTANCE STUDY OF GAAS AL0.3GA0.7AS RESONANT ASYMMETRIC DOUBLE-QUANTUM WELLS WITH SI DELTA-DOPING IN SIDE BARRIERS/

The electro-optical properties of GaAs/Al-0.3,Ga0.7As resonant asymmet ric double quantum wells with Si delta-doping in side barriers have be en investigated by photoreflectance spectroscopy from 20 K to room tem perature. The modulated reflectance spectra consist of Franz-Keldysh o scillations above the Al0.3Ga0.7As band gap, and various excitonic tra nsition 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 reso nance between the narrow well and the wide well subbands. The enhancem ent of the modulated reflectance signal, Delta R/R, at about 50 K also agrees with the subband resonance model.