Subband engineering for p-type silicon ultra-thin layers for increased carrier velocities: An atomistic analysis

TL;DR

This study uses atomistic modeling to analyze how surface orientation and thickness influence hole velocities in ultra-thin p-type silicon layers, revealing optimal configurations for electronic device performance.

Contribution

It provides a comprehensive atomistic analysis of hole velocities in p-type UTB films, highlighting the impact of surface orientation and thickness on carrier velocities and device performance.

Findings

(110) and (112) surfaces yield highest hole velocities.

Velocity increases up to 35% as thickness decreases to 3nm.

Velocity trends correlate with experimental mobility measurements.

Abstract

Ultra-thin-body (UTB) channel materials of a few nanometers in thickness are currently considered as candidates for future electronic, thermoelectric, and optoelectronic applications. Among the features that they possess, which make them attractive for such applications, their confinement length scale, transport direction, and confining surface orientation serve as degrees of freedom for engineering their electronic properties. This work presents a comprehensive study of hole velocities in p-type UTB films of widths from 15nm down to 3nm. Various transport and surface orientations are considered. The atomistic sp3d5s*-spin-orbit-coupled tight-binding model is used for the electronic structure, and a semiclassical ballistic model for the carrier velocity calculation. We find that the carrier velocity is a strong function of orientation and layer thickness. The (110) and (112) surfaces provide the highest hole velocities, whereas the (100) surfaces the lowest velocities, almost 30% lower than the best performers. Additionally, up to 35% velocity enhancements can be achieved as the thickness of the (110) or (112) surfaces is scaled down to 3nm. This originates from strong increase in the curvature of the p-type UTB film subbands with confinement, unlike the case of n-type UTB channels. The velocity behavior directly translates to ballistic on-current trends, and correlates with trends in experimental mobility measurements.