Band structure engineering of a nonlinear optical response in semiconductor superlattices

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Abstract
The authors show that the nonlinear response of certain direct gap semiconductor superlattices is greatly enhanced when the separation of the lowest conduction bands is comparable with the magnitude of the principal gap. The mechanism which results in this enhancement is virtual transitions to higher subbands. Examples of (InAs)1-x(GaSb)x/AlSb superlattices expected to exhibit the enhanced nonlinear response in the near-infrared region of the spectrum are presented. They also investigate nonlinear response in semiconductor superlattices at ultrashort times ( approximately 100 fs). In the authors scheme a full account is given fro the first time of band structure effects upon transients. They then use a three-level model to determine the conditions under which predictions, based on the steady-state response theory and the golden rule, break down in structures with closely spaced energy levels.