Nonresonant carrier transport through high-field domains in semiconductor superlattices

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Abstract
The actual field distribution in superlattices under electric field domain formation is investigated by photoluminescence and Raman spectroscopy. From the measured subband spacings, we determine the magnitude of the field that corresponds to resonant alignment of subbands in adjacent wells. The electron occupation of higher subbands is probed by photoluminescence (PL) measurements. Comparing the results of higher subband PL and the current-voltage characteristics, it is shown that the high-field domain is always nonresonantly coupled with a field strength below the resonance value. The sudden increase in the current when the high-field domain extends over the entire superlattice is explained. Calculations of the field distribution based on a microscopic model support our experimental observations.