Control of electron transitions in nano structures and development of near-and mid-infrared optical modulator devices

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We have explored ways to control optical transitions and carrier scatterings associated with electronic levels and subbands in 10nm-scale quantum wells, quantum wires and quantum dots.We investigated possibilities of using these processes for optical modulator devices.With respect to quantum dots (QDs), we have studied (1) the electric-field induced (Stark) shift of absorption spectrum of stacked QDs, (2) the THz-induced modulation of photoluminessence from strain-induced quantum dots, caused by the redistribution of carriers in this system, and (3) the scattering mechanisms of electrons by charged and neutral QDs placed near the hetero-FET channel. With regards to quantum wires (QWRs), we have clarified (4) anisotropies both in conductivities and polarization dependent optical properties of step QWR structures on vicinal GaAs (111) plane, and (5) the origin of polarization dependent luminescence spectra from ridge QWR structures, caused by the slight asymmetries in the cross-sectional shape of wires. In relation to the intersubband absorption spectra of quantum wells (QWs), we have clarified (6) the origins of gate-voltage dependent absorption spectra, (7) effects of interface roughness on intersubband optical spectra over the wide range of temperatures, and (8) a new bolometric infrared detector scheme, where an n-type QW stack is used as the infrared absorber and a p-type QW is used as the sensor for temperature rise.