QUANTUM TRANSPORT IN ULTRASMALL ELECTRONIC DEVICES

Device analysis has traditionally been based on the semiclassical Boltzmann transport equation. Despite its impressive successes, this approach suffers from an important limitation; it cannot describe transport phenomena in which the wave nature of electrons plays a crucial role. A variety of such quantum effects have been discovered over the years, such as tunnelling, resonant tunnelling, weak and strong localisation, and the quantum Hall effect. Since 1985, experiments on ultrasmall structures (dimensions 100 nm) have revealed a number of new effects such as the Aharanov-Bohm effect, conductance fluctuations, non-local effects and the quantised resistance of point contacts. For ultrasmall structures at low temperature, these phenomena have clearly shown that electron transport is influenced by wave interference effects not unlike those well known in microwave networks. New device concepts are being proposed and demonstrated that are based on these wave properties. The authors review quantum interference effects that have been observed in ultrasmall structures, and their implications for future electronic devices. They also review the theoretical understanding of such phenomena and discuss some of the unresolved questions that have to be answered in order to develop accurate models for quantum device simulation.