Monitoring the applied strain in monolayer gallium selenide through vibrational spectroscopies: a first-principles investigation

Abstract

Monolayer gallium selenide (GaSe) is a promising material for nanoscale electronic, spintronic, and optoelectronic applications. Its electrical conductivity and optical properties were reported to be largely tuned by strain engineering, where the assessment of the applied strain is crucial. In this work, we apply first-principles calculations to unveil the strain-induced phonon frequency shifts in monolayer GaSe, showing its promising application as a strain probe. Furthermore, we find that the uniaxial-, biaxial-, and shear-strain onset for strain-induced lattice instability are 22%, 16%, and 5%, respectively, indicating it could be used as a handle in flexible electronics. We find monolayer GaSe to be about 2 times softer than monolayer MoS2 and 4 times softer than monolayer graphene, and that its Raman fingerprint modes can resolve strain values in the low-strain regime up to 1.0%. These results suggest its use as a strain sensor in fragile applications. Our results provide insight into the use of Raman and infrared spectroscopies to probe the strain in monolayer GaSe, which is of paramount importance for further developments in strain engineering and flexible electronics in GaSe-based devices.