Abstract

Asymmetric coupled quantum wells (ACQWs) were used to study red-Stark shift of the excitons.¹ On the other hand, the blue-Stark shift for the optimized ACQW was predicted.² Here, we report our photo-current measurements (or the optimized ACQW structure at 78K. The optimized ACQW sample was grown using molecular beam epitaxy and consisted of 25 × (a 18-A GaAs well, a 15-A Al_0.4Ga_0.6As tunnel barrier, a 32-A GaAs well, and a 100-A Al_0.4Ga_0.6As separating layer). The water has been processed into mesa diodes with ACQWs in the intrinsic region of p-i-n diode. Argon-pumped cw dye laser was used for photo-current study. Our calculations showed that a field of ~50 kV/cm was required to bring the lowest hole energy levels of two wells into resonance and to increase the oscillator strength of the lowest excitonic transition. Since a built-in field of ~21 kV/cm was measured from I-V curve, the externally applied bias required for resonance was calculated to be about 2.1 V. In our experiment, at the reverse bias ~2.25 V, the sharp increase in the photo-current peak was observed for laser intensity ~9.2 mW/cm², indicating the resonance between the lowest hole levels in the ACQWs and confirmingourpredictions.² We also observed the unusually large blue-Stark shift of the heavy-hole excitons up to 6.1 meV (27 A). The external bias ranges at which the resonance occurs at much narrower than what predicted, and may be explained by the transverse excitonic effect.

© 1990 Optical Society of America