Discrepancies between photocurrent and absorption spectroscopies in intersubband photoionization from GaAs/AlGaAs multiquantum wells

Abstract

Intersubband transitions between a bound state and extended states in GaAs/AlGaAs multiquantum wells are studied by simultaneous absorption and photocurrent spectroscopy under different electric field conditions. It is found that both types of spectra exhibit different line shapes, with the photocurrent maximum occurring at lower photon energy than in absorption spectra. Moreover, there is a blue shift of absorption peak and a red shift of photocurrent peak with increasing electric fields. These results suggest that a sequential mechanism is involved in the photocurrent collection from the quantum well. The blue shift is then well fitted by a quadratic Stark effect and the red shift by a barrier lowering mechanism.