Exciton effects in sequential resonant tunneling of photocarriers in GaAs/AlAs multiple quantum wells

We have studied the sequential resonant tunneling characteristics of coupled GaAs/AlAs quantum wells (QW’s) by measuring the electric-field dependence of the photocurrent and of the excitonic photoluminescence (PL) associated with the first and second conduction subband. If the first subband of a QW is resonantly aligned with the second subband of the adjacent QW, a maximum of the photocurrent, a strong reduction of the PL intensity from the first subband, and a pronounced enhancement of the PL associated with the second subband are observed. Unexpectedly, these resonant extrema are observed at different electric fields. This phenomenon is attributed to the different binding energies of the intrawell and interwell excitons.