Accurate strain measurements in highly strained Ge microbridges

TL;DR

This paper calibrates and refines the Raman spectroscopy method for measuring high tensile strains in germanium microbridges, revealing a non-linear strain-Raman shift relation up to 4.9% strain.

Contribution

It introduces a new calibration of the Raman-strain relation at high strains using synchrotron microdiffraction, improving accuracy beyond previous empirical models.

Findings

Achieved tensile strains up to 4.9% in Ge microbridges

Discovered the non-linearity of the Raman-strain relation at high strains

Provided a more accurate model for strain measurement in highly strained Ge

Abstract

Ge under high strain is predicted to become a direct bandgap semiconductor. Very large deformations can be introduced using microbridge devices. However, at the microscale, strain values are commonly deduced from Raman spectroscopy using empirical linear models only established up to 1.2% for uniaxial stress. In this work, we calibrate the Raman-strain relation at higher strain using synchrotron based microdiffraction. The Ge microbridges show unprecedented high tensile strain up to 4.9 % corresponding to an unexpected 9.9 cm-1 Raman shift. We demonstrate experimentally and theoretically that the Raman strain relation is not linear and we provide a more accurate expression.