Geometric and chemical components of the giant piezoresistance in silicon nanowires

TL;DR

This study investigates the diverse piezoresistance behaviors in silicon nanowires, revealing that stress concentration and surface chemistry significantly influence the magnitude and sign of the PZR effect.

Contribution

It demonstrates that both geometric stress concentration and surface chemical effects are key to understanding the giant and anomalous PZR in silicon nanowires.

Findings

Stress concentration causes giant PZR in SiNWs.

Chemical treatment affects PZR sign and magnitude.

Observed PZR coefficients range from negative to positive values.

Abstract

A wide variety of apparently contradictory piezoresistance (PZR) behaviors have been reported in p-type silicon nanowires (SiNW), from the usual positive bulk effect to anomalous (negative) PZR and giant PZR. The origin of such a range of diverse phenomena is unclear, and consequently so too is the importance of a number of parameters including SiNW type (top down or bottom up), stress concentration, electrostatic field effects, or surface chemistry. Here we observe all these PZR behaviors in a single set of nominally p-type, $\langle 110 \rangle$ oriented, top-down SiNWs at uniaxial tensile stresses up to 0.5 MPa. Longitudinal $\pi$-coefficients varying from $-800\times10^{-11}$ Pa$^{-1}$ to $3000\times10^{-11}$ Pa$^{-1}$ are measured. Micro-Raman spectroscopy on chemically treated nanowires reveals that stress concentration is the principal source of giant PZR. The sign and an excess PZR similar in magnitude to the bulk effect are related to the chemical treatment of the SiNW.