Experimental Investigation of Hole Transport in Strained $\hbox{Si}_{1 - x}\hbox{Ge}_{x}/\hbox{SOI}$ pMOSFETs: Part II—Mobility and High-Field Transport in Nanoscaled PMOS

Abstract

We experimentally studied the high-field transport and mobility in nanoscaled Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1 -</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> Ge <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> /silicon on insulator (SOI) PMOSFETs with gate length down to 17 nm. The study relies on the electrical characterization performed from room temperature down to 20 K. Strain relaxation in short channel has been evidenced by nanobeam electron diffraction, which explains the decrease of hole velocity and mobility with gate length. Despite this strain relaxation, a mobility gain is nevertheless preserved in sub-100-nm SiGe PMOS, with a maximum gain for 20% Ge in the layer. Short-channel mobility extraction reveals a lower contribution of Coulomb scattering for SiGe channel PMOS, which may explain this mobility improvement. We also demonstrate that the short-channel transport is governed by the Ge composition in the SiGe layer, with an optimum concentration of 20% Ge. We have finally evidenced a different temperature dependence of the limiting velocity at high field between SiGe and Si PMOS, suggesting that SiGe transport will be governed by inelastic scattering instead of ballisticity as <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> is shrunk.