Quantum States and Transport Phenomena of Two-and One-dimensional Electrons in In-plane Surface Superlattice Structures

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(A) Research results on Planar Superlattices :A theoretical work has been done on electronic states in grid-inserted (GI) quantum well (QW) structures to show that both quantum wire (QWI) states as well as planar superlattice (PSL) states can be synthesized by setting appropriately the thickness and period of AlAs grids in the middle of GaAs QW layers. Transport properties and interband optical spectra of such GI-QW structures have been studied both experimentally and theoretically. In particular, influences of random potentials on electronic properties in the presence of periodic potential have been assessed ; for example, the negative transconductance characteristic caused by the minigap formation and the polarization anisotropy of optical spectra are examined.(B) Research Results on Quantum Wires :A design theory is developed to analyse the quantum states and concentration Ni of one-dimensional electrons in modulation-doped AlGaAs-GaAs edge-quantum wires. It has been shown that the maximum concentration Ni in the ground subband before filling the second subband is achieved when the quantum well width is set around 200* at which the influence of ionized impurity scattering is minimized. In addition, the interface roughness scattering in the edge quantum wires has been evaluated to show that the scattering can be substantially suppressed when Ni is set above 1-2xlO^6/cm. Transport experiment on wires have been also carried out and new insights have been obtained including the Coulomb blockade.