Scattering theory: a conceptually simple view of nanoscale transistors

With the critical dimensions of transistors now measured in nanometres, questions about atomic scale fluctuations, quantum confinement, quantum transport, off-equilibrium transport and the ultimate performance limits arise. Sophisticated simulation tools will be used with increasing frequency, but advanced device development is still largely guided by a drift-diffusion concept of devices. A simple, physically sound view of transport in nanoscale transistors is needed to interpret simulations and guide experimental work. During the past 15 years, scattering theory (the so-called Landauer approach) provided mesoscopic physicists with a clear conceptual view of quantum transport in mesoscopic structures and guided much of the experimental work in that field (Datta, Electronic Transport in Mesoscopic Systems, Cambridge Univ. Press, 1995). The same approach is now being applied to questions about the resistance of molecular wires and atoms (Datta et al., Phys. Rev. Lett. vol. 79, p. 2530, 1997). The purpose of this paper is to describe a similar approach for treating semiclassical transport in small transistors and to demonstrate that it provides new insights into the device physics of small transistors. The approach has been applied to bipolar transistors and MOSFETs, and can be extended from a phenomenological level to a full solution of the Boltzmann equation.