High mobility high-κ-all-around asymmetrically-strained Germanium nanowire trigate p-MOSFETs

Abstract

We demonstrate for the first time, asymmetrically strained Ge, high-κ/metal gate nanowire (NW) trigate p-MOSFETs with record hole mobility of 1490 cm2/Vs. This mobility is 2x above on-chip, biaxially strained Ge planar FETs and ∼15x above Si universal mobility. The fabrication approach features: (1) a new strained Si/strained Ge/HfO2 NW channel materials stack, with HfO2 dielectric at the bottom which acts as an excellent etch stop for top-down NW formation, and also unpins the back Ge-dielectric interface, (2) large compressive biaxial strain (∼2.5%) that is built into the channel material prior to layer transfer, and (3) lateral strain relaxation by nanoscale patterning of the channel. The resulting asymmetric strain distribution dramatically reduces the conductivity effective mass. 6×6 k.p quantum mechanical simulations predict an increase in the Ge NW average inverse effective mass by a factor of 1.6 relative to planar biaxially strained Ge, consistent with the measured 2x mobility enhancement. © 2012 IEEE.