Atomistic effects: the uncontrolled presence of individual impurity atoms may have a devastating influence on actual devices by blocking or disrupting the quantum flows. When there are just a few impurities the effects do not average out.
In 1986 Alan Fowler of IBM T J Watson Labs in New York visited our theory group at Glasgow University and showed John Davies and me some curious results on the conductance of small transistors. On investigation we surmised that the discrete nature of individual impurity atoms was having a direct influence on the behaviour of a relatively large device. Such atomistic effects are nowadays considered to be killer effects for the continued down-scaling of transistors and they have become the focus of considerable study particularly by the Device Modelling group at Glasgow. In the late 1980s work by the Glasgow group showed that atomistic effects (fluctuation potential) could dominate the recently devised mesoscopic quantum devices such as quantum point contacts, throttles and ring-structured interference devices. The above figure shows a schematic of individual impurity atoms in otherwise perfect two-dimensional electron gas nanostructures (the space scales are less than one micron).
References
“Fluctuations in sub-micron semiconducting devices caused by the random position of dopants”
J Nixon, J H Davies and J R Barker,
in Physics and fabrication of nanostructures, ed M Read and W. P. Kirk,Academic Press 123-127(1989)
“Theory of non-linear transport in quantum waveguides”
J. R. Barker, M. Finch, J. Pepin and M. Laughton
Solid State Electronics 32 1155-1159 (1989)
“Modal analysis of transport through quantum point contacts using realistic potentials”
Laughton M.J, Barker, J R Nixon J A and Davies J H
Phys. Rev. B 44 1150-1153 (1991).
“Granular nanoelectronics”
J. R. Barker
in Physics of granular electronic systems, edited by D K Ferry, J R Barker, C Jacoboni, Plenum 327-342(1991).
“Introduction to quantum transport in electron waveguides”
Barker J.R
in Physics of granular electronic systems, edited by D K Ferry, J R Barker, C Jacoboni, Plenum,19-41 (1991).