Measurements of absolute bandgap deformation-potentials of optically-bright bilayer WSe$_2$

TL;DR

This study experimentally measures the deformation potentials of bilayer WSe$_2$ at key points in the Brillouin zone, revealing how strain influences its optoelectronic properties and enabling precise strain engineering for advanced devices.

Contribution

First experimental determination of absolute deformation potentials for bilayer WSe$_2$ at multiple high-symmetry points using local biaxial strain and photoluminescence spectroscopy.

Findings

Deformation potential for Q$_{c}$-K$_{v}$ is -5.10 ± 0.24 eV.

Deformation potential for K$_{c}$-K$_{v}$ is -8.50 ± 0.92 eV.

Approximately 0.9% biaxial tensile strain converts bilayer WSe$_2$ from indirect to direct bandgap.

Abstract

Bilayers of transition-metal dichalcogenides show many exciting features, including long-lived interlayer excitons and wide bandgap tunability using strain. Not many investigations on experimental determinations of deformation potentials relating changes in optoelectronic properties of bilayer WSe$_2$ with the strain are present in the literature. Our experimental study focuses on three widely investigated high-symmetry points, K$_{c}$, K$_{v}$, and Q$_{c}$, where subscript c (v) refers to the conduction (valence) band, in the Brillouin zone of bilayer WSe$_2$. Using local biaxial strains produced by nanoparticle stressors, a theoretical model, and by performing the spatially- and spectrally-resolved photoluminescence measurements, we determine absolute deformation potential of -5.10 $\pm$ 0.24 eV for Q$_{c}$-K$_{v}$ indirect bandgap and -8.50 $\pm$ 0.92 eV for K$_{c}$-K$_{v}$ direct bandgap of bilayer WSe$_2$. We also show that $\approx$0.9% biaxial tensile strain is required to convert an indirect bandgap bilayer WSe$_2$ into a direct bandgap semiconductor. Moreover, we also show that a relatively small amount of localized strain $\approx$0.4% is required to make a bilayer WSe$_2$ as optically bright as an unstrained monolayer WSe$_2$. The bandgap deformation potentials measured here will drive advances in flexible electronics, sensors, and optoelectronic- and quantum photonic- devices through precise strain engineering.