| 摘要 |
Semiconductor electrooptic medium shows behavior different from a medium based on quantum confined Stark Effect. A preferred embodiment has a type-II heterojunction, selected such, that, in zero electric field, an electron and a hole are localized on the opposite sides of the heterojunction having a negligible or very small overlap of the wave functions, and correspondingly, a zero or a very small exciton oscillator strength. Applying an electric field results in squeezing of the wave functions to the heterojunction which strongly increases the overlap of the electron and the hole wave functions, resulting in a strong increase of the exciton oscillator strength. Another embodiment of the novel electrooptic medium includes a heterojunction between a layer and a superlattice, wherein an electron and a hole in the zero electric field are localized on the opposite sides of the heterojunction, the latter being effectively a type-II heterojunction. Yet another embodiment has a heterojunction between two superlattices, wherein an electron and a hole in a zero electric field are localized on the opposite sides of the heterojunction, the latter operating effectively as a type-II heterojunction. A further embodiment has an ultrathin quantum well layer confined by barrier layers, having an essentially different barrier heights and a thick layer, wherein, in a zero electric field, a charged particle of one sign having a large effective mass is localized in this ultrathin layer, and a particle having a different sign of the charge, having a small effective mass is not localized in this ultrathin layer, but is localized mainly in the neighboring thick layer. Thus, the heterojunction between the two layers operates effectively as a type-II heterojunction. Applying an electric field to all types of the electrooptic medium of the present invention results in a dramatic increase of the exciton oscillator strength and, therefore, in a large positive refractive index change at the photon energies below the exciton absorption peak. A very strong increase in the optical transition photon energy can be achieved, when necessary.
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