Monte carlo study of germanium N- and P- MOSFETs

Abstract

As device dimensions are being scaled to their ultimate limits, channel mobility engineering seems to offer one of the best prospects of improved performance of metal oxide semiconductor field effect transistors (MOSFETs). In fact, new materials, such as Ge, with higher effective mobilities of electrons (2times) and holes (4times) than in Si are already being explored to increase the drive currents in MOSFETs. In addition, by straining the Ge channels, it is possible to further increase the mobilities of the holes. However, how this advantage in mobility translates to improved drive current in the short-channel length MOSFETs is not completely clear. For example, in the ballistic limit, it is thermal velocity that matters (Lundstrom, 1997) and these are comparable for Si and Ge. Although, there have been reports from some experimental and theoretical (in the ballistic limit) studies of the mobility and drive current enhancements of unstrained and strained Ge channel MOSFETs over Si MOSFETs, no Monte Carlo simulation taking into account full band structure, scattering, non local field effects, etc., has so far been been performed. The aim of this work was to perform a full band Monte Carlo simulation study of unstrained Ge bulk N- and P- MOSFETs and strained Ge bulk PMOSFETs and compare with their Si counterparts. Since biaxial strain along the (100) plane in Ge does not break the degeneracy of the conduction band L valleys of Ge, we have not considered strained Ge NMOSFETs