Photocurrent spectroscopy of GaAs/AlxGa1−xAs quantum wells in an electric field

A photocurrent spectroscopy study has been made of p-i-n photodiodes in which the intrinsic regions were composed of GaAs/${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As quantum wells. A sequence of distinct exciton absorption peaks was observed in the photocurrent spectra. Biasing the diodes allowed the effects of electric fields on the excitons to be examined. A comparison was made of the shifts of the energies of the excitons with applied field (Stark shifts). Changes in the relative amplitudes of the exciton peaks with bias were also noted. The Stark shifts for excitons in quantum wells with AlAs barriers were smaller than for wells with ${\mathrm{Al}}_{0.3}$ ${\mathrm{Ga}}_{0.7}$As barriers. Explanations for these observations are given.