Nonthermal occupation of higher subbands in semiconductor superlattices via sequential resonant tunneling.
The occupation of excited subbands in GaAs-AlAs superlattices under the ap-plication of an electric field perpendicular to the layers is directly observed in photoluminescence experiments. The coupling between adjacent wells at certain electric fields leads to a significant occupation of the respective higher subbands via resonant tunneling. The relative occupation of the second subband at the resonance field is used to determine the intersubband relaxation time. The effect provides a direct verification of the sequential resonant tunneling process in superlattices.