ANALYTICAL MODELING OF THRESHOLD VOLTAGES IN p-CHANNEL Si/SiGe/Si MOS STRUCTURES

Abstract-An analytical model for the threshold voltages in a Si/SiGe/Si MOS structure is presented. It offers very good accuracy as compared to results of one- and two-dimensional numerical simulations. It is shown that short-channel effects lower the threshold voltage of the SiGe channel and increase the threshold voltage for parasitic conduction in the Si-cap layer. The model can serve as a useful tool for p-channel Si/SiGe/Si MOSFET design. NOTATION gate oxide capacitance per unit area contribution of holes to the electric field in the SiGe film Boltzmann constant effective channel length intrinsic carrier concentration doping concentration in the bulk of the semicon-ductor effective doping concentration in the bulk of the semiconductor valence band density of states in silicon valence band density of states in SiGe hole concentration hole concentration at the top heterointerface hole concentration at the surface electron charge fixed oxide charge at the Si-SiO, interface charge in the buried channel charge in the surface channel ratio of semiconductor permittivities in silicon and SiGe respectively temperature build-in voltage of the drain-substratep-n junction drain voltage effective drain voltage gate voltage threshold voltage at the top SiGe/Si heterointerface threshold voltage at the silicon cap surface Ge content in the SiGe film silicon buffer thickness silicon cap thickness depletion layer width gate oxide thickness SiGe film thickness conduction band offset between SiGe and Si valence band offset between SiGe and Si gate voltage window SiO, permittivity silicon permittivit