Study of ballistic transport in Si-CoSi2-Si metal base transistors

Abstract

The hot-electron transfer ratio from the Schottky emitter diode to the Schottky collector diode through the thin base layer of Si-CoSi2-Si metal base transistors has been measured in devices for which the pinhole contribution to the current gain is shown by transconductance measurements to be negligible. The common-base current gain α of the transistors, measured as a function of temperature and base thickness, exhibits an exponential dependence on CoSi2 film thickness, from which a ballistic mean free path is deduced. This value is in good agreement with the mean free path deduced from conductivity data, both at 77 and 300 K. The behavior of the pre-exponential coefficient, i.e., the gain extrapolated to zero base thickness, is not completely understood and shows evidence for hot-electron and space-charge effects in the epitaxial overgrown Si material of the emitter.