Short-channel effects in Si/Si 1− xGe x retrograde double quantum well p-MOSFETs

Abstract

Analytical investigation of short-channel effects in retrograde double quantum well Si 1− x Ge x -channel p-MOSFETs with effective channel lengths in the deep-submicron regime is addressed. The short-channel effects are accounted for by treating the short-channel device as a long-channel one with an apparently-reduced doping density which depends on the channel length and the gate/drain bias. The analysis focuses on the threshold voltage reduction, the gate voltage window, and the hole densities in the quantum wells. The model predicts significant differences in the threshold voltage reduction in the different channels of the device. The reduction is negligible in the surface parasitic channel, fairly small in the second quantum well (channel 2) below the surface channel, and relatively pronounced in the first quantum well closer to the depletion region (channel 1). Accordingly, the gate voltage window increases significantly. The hole density in the different channels has also been found to be appreciably influenced by decreasing channel length. The validity of the model is confirmed by comparing analytical calculations with available experimental and numerical results. These investigations can be used as guidelines for scaling Si/Si 1− x Ge x devices as they illustrate the degrees of freedom available to the Si/Si 1− x Ge x MOSFET designer.