Electric-field domains in semiconductor superlattices: Resonant and nonresonant tunneling.

Photoluminescence experiments detecting the occupation of higher subbands in GaAs-${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As superlattices are used to determine the field strengths of electric-field domains. While the magnitude of the electric field in the low-field domain corresponds to resonant alignment of subbands in adjacent wells, the field strength in the high-field domain is below the value corresponding to the resonant field. These results are interpreted in terms of a simple model based on current conservation.