Large excitonic optical nonlinearity in optimized asymmetric coupled quantum wells

Abstract

Asymmetric coupled quantum wells (ACQWs) were used to observe red-Stark shift1 and optical nonlinearity.2 On the other hand, the blue-Stark shift3 for the optimized ACQWs and large optical nonlinearity4 were proposed. Here, we report our photocurrent measurements performed at 78 K for the optimized ACQW structure and confirm the prediction in Ref. 2. The optimized ACQW sample was grown using molecular beam epitaxy and consisted of 25 × (a 18-Å GaAs well, a I5-Å Al0.4 Ga0.6As tunnel barrier, a 32-Å GaAs well, and a 100-Å Al0.4 Ga0.6As separating layer). The wafer 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. At the lower laser intensity ~9.2 mW/cm2, the unusually large blue-Stark shift of the heavy-hole excitons up to 6.1 meV (27 Å) was observed. As the laser intensity increased, we also observed the intensity-enhanced blue-Stark shift up to ~10 meV (44 Å) at laser intensity ~270 mW/cm2. At the constant reverse bias of ≃3 V the red-Stark shift of the excitons up to 4.9 meV (22 Å) was observed, as the intensity increased from 9.2 mW/cm2 to 850 mW/cm2. The external reverse bias at which the resonance occurs increase as the laser intensity increases. The large optical nonlinearity in this structure may be attributed to the excitonic many-body effects.