INPLANE TRANSPORT-PROPERTIES OF SI/SI1-XGEX STRUCTURE AND ITS FET PERFORMANCE BY COMPUTER-SIMULATION

Transport properties of ungated Si/Si1-xGex are studied by an ensemble Monte Carlo technique. The device performance is studied with a quantum hydrodynamic equation method using the Monte Carlo results. The phonon-scattering-limited mobility is enhanced over bulk Si, and is found to reach 23000 cm2/Vs at 77 K and 4000 cm2/Vs at 300 K. The saturation velocity is increased slightly compared with the bulk value at both temperatures. A significant velocity overshoot, several times larger than the saturation velocity, is also found. In a typical modulation-doped field-effect-transistor, the calculated transconductance for a 0.18 mum gate device is found to be 300 mS/mm at 300 K. Velocity overshoot in the strained Si channel is observed, and is an important contribution to the transconductance. The inclusion of the quantum correction increases the total current by as much as 15%.