Control of electrons and holes by quantum rings and related nanostructures and its device applications

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To expand the forefront of nanoelectronics research, we have explored potentials of quantum ring (QR) structures in parallel with quantum dots (QDs), rods, and wires. Attentions have been focused mainly on type II GaSb based nanostructures, where holes are selectively confined, while electrons are driven outside. Two schemes for the self-organized formation of (GaAl)Sb QRs have been studied; in one scheme, ring-shaped quantum states of holes are formed, whereas electrons are confined in ring-like orbits just outside a positively charged GaSb QD in the other. A possibility to generate multi-pole radiations by making use of QR states has been proposed and analyzed. A new photodetector device has been proposed and realized, in which photo-generated holes are trapped by GaSb holes and modulate the current flow through a near bye channel. In addition, we have demonstrated a unique scheme to align InGaAs QDs along multi-atomic steps of about 20-40nm in periodicity and also novel single-electron transistors based on tiny electrodes attached to an individual InAs QD.