The header shows a computation for the probabilistic charge density of a single electron passing along a semiconductor two-dimensional channel constrained as a ring structure: an Aharonov-Bohm interference device (see the review: “Fundamental aspects of quantum transport theory”, J R Barker,in Handbook on Semiconductors, volume 1 Basic Properties of Semiconductors , Landsberg, P., ed., Second Completely Revised Edition, (:Elsevier-North Holland, Ch 19, 1079-1128( 1992)

I have been investigating the potential of nanoelectronics since the 1970s. At that time the smallest transistors had channel lengths of about 10 microns and the idea of building transistors with channel lengths of 20 nm (nanometers) and even smaller was regarded as fatuous! It was apparent from our theoretical studies that the true limit for practicable devices was around the 6 nm scale but special devices could have atomic dimensions (single electronics). Even a single electron device is not the limit: classically one electron just represents one bit-it is either there or not there! However, in a quantum confined structure one electron can exist in many different quantum states (the concept of qu-bits then leads to quantum computing – a dream for future computer). A surprising result from our studies in the seventies and eighties was that the underlying behaviour of electrons in transistors below one micron in channel length is highly quantum mechanical. Previously it had been thought that each electron passing along the channel of a transistor would undergo a large number of scattering events for example with impurities, lattice vibrations (phonons). Thus the electron flow would be incoherent and the wave nature of the electron would not be manifest.  In fact the average coherence length for an electron regarded as a wave may be much longer than the device itself as dissipative collision processes are relatively infrequent in correctly designed structures. One characteristic of quantum flows of electrons for example is the occurrence of quantized vortices in the flow. These cause tiny trapped regions of charge that block the overall flow and reduce the conductance of the channel.

Next: Typical Nanostructures

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