Quantum Confinement Effects in Extremely Thin Body Germanium n-MOSFETs

Abstract

We explore the impact of varying channel thickness (from 8 to 1.5 nm) on extremely thin germanium n-MOSFETs, by explicitly incorporating the quantum confinement effects in the band structure calculations using the first principle density functional theory. In Ge (001) thin films in the sub-10-nm regime, the X valley becomes the lowest conduction band valley and is mostly responsible for the charge transport as in silicon. Considering device parameters as per the international technology roadmap for semiconductors (ITRS) projected device specifications for the year 2024, we use the confinement-modulated effective mass to calculate the drain current employing the fully ballistic nonequilibrium Green's function transport model. The best suited thickness for digital applications is found to be 1.5 nm with subthreshold slope of 83.8 mV/decade, I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> of 1.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> , and an I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> exceeding ITRS targets.