Effect of Germanium content on mobility enhancement for strained silicon FET

This paper reports on mobility enhancement in the strained silicon (Si) based field effect transistor (FET) structure corresponds to variation of germanium (Ge) content. The investigations were performed via Silvaco TCAD virtual fabrication and characterizations platforms, ATHENA and ATLAS tools, respectively. In this study, it involved physical modelling of both conventional and strained Si FETs for comparison. The doping dose of the polysilicon was manipulated from 1.0 × 10
¹³
to 4.2 × 10
¹⁴
cm
^-2
which results in variation of the channel length from 90 nm to 22 nm. The threshold voltage of both structure had been compared where for the case of the conventional FET, the threshold voltage decreased as the channel length decreased. Accordingly, as the channel length of strained Si FET decreased, the threshold voltage increased with the Ge content in the channel that varied from 10% to 90%. The sub-threshold voltage was observed to increase as the strained Si FET entered the short channel regime, however it continued to slightly decrease as it went deeper into the sub-nanometer technology node. The strained Si FET had up to ~4.2 times carrier mobility enhancement compared to that of conventional FET as the mole fraction of Ge increased in the Si
_1-x
Ge
_x
layer of the strain channel. The presence of Ge in the strain layer at the channel has been proved to further enhance the mobility thus improving the drive current. Large drive current aids to the faster switching speed of the transistor, making the circuits to run at higher clock rates.