Interference Effect of Electron Waves in Quantum Wires Fabricated by Focused Ion Beam Implantation

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The purposes of this work are : (i) to develop fabrication processes of the device structures based on quantum wires by means of focused ion beam(FIB) implantation, and (ii)to understand the electron transport mechanisms in the quantum wire structures fabricated by the FIB implantation. In this year, we have studied the electron scattering at the boundaries of the quantum wires. We systematically studied the specularity factor p, which is the probability of specular scattering at the boundary, for various carrier densities N_s and wire widths W.We defined quantum wires by locally destroying the conductivity of a two dimensional electron gas by FIB implantation. Two types of wire structures were fabricated ; one is a 1mum-wide Schottky-gated wire, and the other an in-plane-gated wire. From measured positive magnetoresistance, p and W were derived based on the classical theory for the boundary scattering When N_s was varied from 2X10^<15>m^<-2>to 3.7X10^<15>m^<-2> in a Schottky-gated wire, p was found to be nearly 0.6 and almost independent of N_s. This fact suggests that the scatterer near the boundary has a shortーranged delta-function like potential. On the other hand, when W was varied from 0.6mum to 0.4mum in an in-plane-gated wire, p was found to depend strongly on W and increase from 0.45 to 0.8. When p is plotted as a function of DELTAd, the distance between the ion implanted position and the boundary of the conducting channel, all data fall on a single curve, which strongly suggests that the scatterers are generated by ion implantation and that the DELTAd dependence of p reflects the spatial distribution of the scatterers. We consider that the most important diffusive scatterers which exist near the boundary are point defects caused by struggling ions.