Recent rapid progress of semiconductor nano-fabrication technology enables us to manipulate single electrons using conductive nano-scale "island" and wires coupled through tunneling barrier structures. These single electron devices are novel candidates for next generation of electron devices because of extremely low power consumption. Compound semiconductors such as GaAs, AlGaAs, InGaAs etc offer intrinsically higher speed and low noise devices than Si, and used to develop very high frequency electronic devices and circuits for microwave and wireless communication applications. We present a novel fabrication method of uniform GaAs dot structures using selective area metalorganic vapor phase epitaxy (MOVPE), and their application to single electron transistors (SETs) and their logic circuits.

AlGaAs/GaAs single quantum well structures were grown on SiNx masked (001) GaAs substrates which have wire-like openings formed by electron beam lithography and wet chemical etching. Crystal growth occurs only on the opening area and the structure has sidewall facets which are stable surfaces. During growth, the top surface width becomes smaller than the opening width of the substrate. GaAs nano wire structures are obtained using this unique nanostructure formation method.

Subsequently, GaAs quantum dot and wire coupled structures are formed on a masked substrate having a wire-like opening with width modulation. Tunneling barriers and quantum dots are naturally formed at narrow and wider parts of wire because of the quantum effect. This leads to the successful formation of a single electron transistor. By applying gate bias voltage on the quantum dot, Coulomb gaps and their modulation are apparent in their transport properties near the pinch-off voltage at 2K. Electron spin interaction effect is also observed between electrons in a dot and an electrode (Kondo effect) at low temperature transport properties. New architecture suitable for single electron logic circuit is designed, and preliminary "NAND" logic circuits are successfully demonstrated.


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