Electric field dependence of exciton transition energies in GaAs-${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As quantum wells studied by photocurrent spectroscopy

Photocurrent spectroscopy of GaAs-${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As multiple-quantum-well structures in an electric field perpendicular to the heterointerface is used to study exciton transition energies as a function of electric field up to ∼${10}^5$ V/cm. A large number of excitonic transitions, as many as 16, are identified. The Δn≠0 forbidden excitonic transitions grow in intensity with increasing electric field, whereas the Δn=0 allowed excitonic transitions show the opposite. Both negative and positive shifts of exciton transition energies are observed. The results of these observations are compared with those of a theoretical calculation based on a multiband effective-mass approach which incorporates valence-band mixing effects, and a good agreement is found.