Electronic properties and transition processes in semiconductor quantum box structures and artificially localized states (super-donors)

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As for artificially localized states, namely, the magnetic quantum box (Mag-QB) systems consisteing of quantum wells at magnetic fields, Coulomb quantum box (Imp-QB) systems formed at impurity, levels in quantum wells, and quantum boxes by nanofabrication technique (Fab-QB), we have studied following three subjects.First, we observed longitudinal magnetophonon resonances in superlattices, tunnelling processes through Landau levels in triple barrier tunnel diodes at magnetic fields, and two-dimension (2D) -0D-2D tunnelling through donor levels in double barrier tunnel diodes. In addition, we observed turnstile motion and photon-assisted tunnelling in an electron-beam-fabricated QB.We also fabricated self-assembled InAs quantum boxes and carried out transport measurements.Second, we examined energy relaxation in super-donor levels in order to clarify presence of phonon bottle-neck both theoretically and experimentally. Our theory showed existence of phonon bottle-neck, and Bloch oscillations in 1D coupled quantum box structures due to suppression of phonon scattering. However, the possibility of relatively fast decay within a few meV at resonance relating to both optical and accoustical scatterings were demonstrated. Experimentally, both transport properties of a triple barrier resonant tunnel structure at magnetic fields and optical analysis of a fast relaxation process in electron-hole systems in quantum wells at magnetic fields suggested presence of fast relaxation process.Third, as for photon excitation and ionization of super-donor states, we investigated controllability of donor levels, temperature dependences of conductivity, and infrared response by introducing Si acceptors in (311) A quantum wells.