Optical nonlinearities of hybrid direct-indirect wannier excitons in polytype double quantum well structures

We have calculated the nonlinear optical properties of a double QW structure, where it is possible to achieve a resonance between a real space direct exciton dir) (electron and hole both confined in the same well) and a real space indirect exciton \ind) (electron and hole confined in separated wells). \dir) and \ind) are coupled by electron tunneling between the two QWs, so that the true excitonic eigenstates are the hybrid direct-indirect excitons. Because of the reduced electron-hole overlap, the \ind) oscillator strength is negligible compared to \dir), but owing to the electron-hole charge separation, it does have large nonlinear properties. Apart from the above electro-optic effect, many-body nonlinearities (due to large two-dimensional Bohr radii) are significant. We have applied our model to the realistic polytype AlSb/InAs/AlSb/GaSb/AlSb structure.