A two-qubit system made of electrons running along coupled pairs of quantum wires is described and numerically analyzed. A brief review of the basic gates is given first, based on preliminary investigations, followed by the description of the electron dynamics. A detailed analysis of a conditional phase shifter is carried out by means of a time-dependent Schrodinger solver applied to a two-particle system. A quantum network suitable for creating entanglement is simulated, and results are shown. The physical structure of the proposed network is within the reach of a solid-state implementation. The physical parameters used in the computations have been chosen with reference to silicon quantum wires embedded in silicon dioxide.

The fabrication of InAlAs wire structures and InGaAs quantum wire structures on non-planer InP substrates with truncated ridges by molecular beam epitaxy is demonstrated. Indium-rich InAlAs epitaxial layers grown on top of ridges exhibit self-formation of electron-confining InAlAs wire structures. The InAlAs layers on top of the ridges lattice-matched to the substrate are obtained by the control of In flux during the growth. The InGaAs quantum wire structures have been fabricated on thus composition-controlled InAlAs barrier layers. The optical properties of the InGaAs quantum wires with composition-controlled InAlAs barrier layer are found to be better than that of the wires without compositional control.

The edge of a thin SOI (silicon on insulator) film was used to form a very narrow Si-MOS inversion layer. The ultra-thin SOI film was formed by local oxidation of SIMOX wafer. The thickness of the SOI film is less than 15 nm, i.e., the channel width is narrower than 15 nm. At low tempera-tures, clear and large conductance oscillations were seen in this edge channel MOSFET. These oscillations are explained by Coulomb blockade effects in the narrow channel with several effective potential barriers, since the SOI film is so thin that the channel current is seriously affected by small potential fluctuations in the channel. These results suggest that the channel current in edge quantum wire MOSFET can be cut off even with a small controlled potential change. Furthermore, we fabricated a double-gate edge channel Si-MOSFET. In this device, the channel current can be controlled in two ways. One way is to control the electron number inside the isolated electrodes. The other way is to control the threshold voltage of MOSFET. This device enables us to control the phase of Coulomb oscillation.

Fabrication methods of novel silicon quantum wires and dots using anisotropic wet chemical etching and thermal oxidation are newly proposed. The method realizes fine Si quantum wires, which are fully surrounded by the thermal SiO2 without any defects. The wires are straight and the Si/SiO2 interfaces are fairly flat. The 10 nm width wires are confirmed by Transmitting Scanning Microscopy observation in minimum size. The fine quantum dots are also fabricated using this method. The characteristics of the wires are investigated and the current oscillations in variation with the gate voltage are observed in low temperature. We believe the origin of these oscillations arise from one-dimensional subband conduction.

Ultrathin GaAs, AlGaAs and GaAs/InAs wire crystals (whiskers) as thin as 20-50 nm are grown by organometallic vapor phase epitaxy (OMVPE) using Au as a growth catalyst. It is found that the whisker shape and width can be controlled by adjusting the thickness of the Au deposited on the substrate surface and the substrate temperature duing OMVPE. A new technique employing a scanning tunneling microscope (STM) for controlling the whisker growth position on the substrate surface is described. Photoluminescence spectra from the GaAs whiskers show a blue shift of the luminescene peak energy as the whisker width decreases. The amount of blue shift energy is rather small compared to that calculated by a simple square potential well model. The discrepancy is explained by the cylindrical potential well model including the surface depletion effect. Atomic composition within the portion of 1-20 nm along the AlGaAs and GaAs/InAs whiskers has been analyzed by energy dispersive X-ray analysis in combination with transmission electron microscopy. This shows the exsitence of Au at the tip of the whisker and the composition change occurs over a length of less than 5 nm at the GaAs/InAs heterojunction.

The potential distribution around a linear array of donor atoms in a semiconductor crystal is calculated, approximating the linear array by a continuous line charge. Two methods are used for the analysis. One is the self-consistent calculation of Poisson's equation and the effective mass Schrödinger's equation, and the other is the Thomas-Fermi approximation. Results of both methods agree very well, and it is shown that it is possible to form a potential distribution as fine as the electron wavelength by appropriate arrangement of the impurity atoms. Arrays of impurity atoms therefore can act as buiding elements for future electron wave devices.

Several issues on semiconductor lasers with low dimensional quantum systems are discussed. First, described are fabrication techniques for quantum wire and box structures, particularly a selective growth MOCVD growth technique which have been recently developed. Using this technique, we obtained 20 nm15 nm triangular-shaped quantum wire structures. Next, we investigate band structures of the quantum wires having strain effects, including lasing characteristics of quantum wire lasers with the strain effects. Finally we discuss importance to control both the electron wave mode and the optical wave mode for future high performance lasers, which leads to the concept of quantum micro-lasers. In order to demonstrate possibility to control the spontaneous mode in the laser cavity, an experimental result is shown on enhancement and inhibition effects of the spontaneous emission mode in a vertical cavity laser having two kinds of the quantum well.

Several issues on semiconductor lasers with low dimensional quantum systems are discussed. First, described are fabrication techniques for quantum wire and box structures, particularly a selective growth MOCVD growth technique which have been recently developed. Using this technique, we obtained 20 nm 15 nm triangular-shaped quantum wire structures. Next, we investigate band structures of the quantum wires having strain effects, including lasing characteristics of quantum wire lasers with the strain effects. Finally we discuss importance to control both the electron wave mode and the optical wave mode for future high performance lasers, which leads to the concept of quantum micro-lasers. In order to demonstrate possibility to control the spontaneous mode in the laser cavity, an experimental result is shown on enhancement and inhibition effects of the spontaneous emission mode in a vertical cavity laser having two kinds of the quantum well.