Ballistic transport in semiconductor devices

"Ballistic" transport of electrons or holes, which can occur in Si and GaAs devices on distance scales of the order of tenths of microns, is transport unimpeded by interactions with the crystal lattice itself, with lattice defects, with impurities, or with interfaces - i.e., transport akin to that of a bullet in free space. Without the "drag" exerted by such interactions, charge carriers can achieve velocities several times those in larger devices, with a consequent multiplication of device speed. While it is difficult to achive pure ballistic transport, speeds can, nevertheless, increase somewhat as device sizes approach carrie mean free paths. This paper will discuss the nature of electron transport in devices so tiny that the familiar relationships between velocity and field with which materials have usually been described, no longer apply.