Strained-$\hbox{Si}_{1 - x}\hbox{Ge}_{x}/\hbox{Si}$ Band-to-Band Tunneling Transistors: Impact of Tunnel-Junction Germanium Composition and Doping Concentration on Switching Behavior

Strained pseudomorphic Si/Si
_1-x
Ge
_x
/Si gate-controlled band-to-band tunneling (BTBT) devices have been analyzed with varying Ge composition up to 57% and p+ tunnel-junction (source) doping concentration in the 10
¹⁹
-10
²⁰
cm
^-3
range. Measurements show the impact of these parameters on the transfer and output characteristics. Measurements are compared to simulations using a nonlocal BTBT model to analyze the mechanisms of device operation and to understand the impact of these parameters on the device switching behavior. The measured characteristics are consistent with simulation analysis that shows a reduction in energy barrier for tunneling (E
_geff
) and a reduction in tunneling distance with increasing Ge composition and source doping concentration. Increases in the pseudomorphic layer Ge content and doping concentration of the tunnel junction produce large improvements in the measured switching-behavior characteristics (I
_on
, slope, turn-on voltages, and sharpness of turn-on as a function of V
_ds
). Simulations are also performed to project the potential performance of more optimized structures that may be suitable for extremely low power applications (V
_dd
< 0.4 V).