Built-in longitudinal field effects in sub-100-nm graded Si1-xGex channel PMOSFETs

Simulations and experiments have been conducted to study the built-in longi tudinal field effects in sub-100-nm graded Si1-xGex channel vertical pMOSFE Ts. Results are compared for two operation modes with the source/drain (S/D ) contacts interchanged, i.e., the "normal" mode, in which the built-in fie ld is favorable to the drift, and the "reverse" mode, in which the built-in held is a retarding one. The linear drain current at V-DS = -0.1 V is foun d to be very similar between the two modes. Furthermore, if the body is gro unded, the saturation drain current, as simulated, in the normal mode is 20 % lower than that of the reverse mode. With floating body effects, however, experimentally it is observed that the saturation drain current in the nor mal mode is 14% higher than in the reverse mode. The simulation reveals tha t in the linear condition, the benefits of the accelerating built-in field in the channel is negated by a weaker source injection resulting from a lar ger source-side built-in potential at the Si source junction, and also by a reduced or even reversed diffusion current in the normal mode; in the satu ration condition, the built-infield is overshadowed by the large external f ield due to high drain biases. The measured off-state leakage current at V- DS = -1.6 V in the normal made is 100 times higher than in the reverse mode due to the floating body effects.