Tunneling and relaxation of photogenerated carriers in semiconductor quantum wells

The competition between tunneling (vertical transport) and relaxation (exciton formation) of photogenerated carriers in GaAs-${\mathrm{Al}}_{0.29}$ ${\mathrm{Ga}}_{0.71}$As multiple quantum wells in an electric field has been studied by means of nonlinear luminescence and photocurrent measurements and time-correlated single-photon counting. The nonlinearity is brought about by an exciton formed by bimolecular processes. The nonlinear luminescence and photocurrent signals are qualitatively explained in terms of the competition between tunneling and relaxation. Furthermore, the heavy-exciton luminescence shows two exponential decays when the electric field is 10–29 kV/cm. The slow component is ascribed to excitons formed by the bimolecular processes as a result of multiple successive processes of tunneling, relaxation, and exciton dissociation. Under the resonant electric field $F_r$=29 kV/cm, where electron sequential resonant tunneling occurs, the slow component diminishes because of the increase of the electron tunneling rate.