Dramatic enhancement of low electric-field hole mobility in metal source/drain Ge p-channel metal-oxide-semiconductor field-effect transistors by introduction of Al and Hf into SiO2/GeO2 gate stack

Abstract

Ge p-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) are fabricated using HfGe metal source/drain contacts and an Al/SiO2/GeO2 gate stack. Following postmetallization annealing at 400 °C, the MOSFET shows peak field-effect mobility (μh) of 336 cm2/Vs. Insertion of a Hf layer between the Al and SiO2 layers increases the peak μh to 919 cm2/Vs, which is associated with a positive shift of threshold voltage. We propose a model involving compensation of positive interface trapped and oxide fixed charges by negative oxide fixed charges introduced by Al and Hf in the gate stack. This leads to a decrease in Coulomb scattering, dramatically enhancing mobility.