Giant elasto-optic response of gallium selenide on flexible mica

Understanding the bending behaviour of a crystal onto a flexible platform is crucial for flexible electronics. The Young’s modulus, a measure of how easily a material deforms, plays a critical role in the coupled deformation of a crystal on a flexible substrate, as well as the transfer of strain from the substrate onto the layer. Here, we report on the bending behaviour of gallium selenide (GaSe), a van der Waals semiconductor with a small Young’s modulus and strain-dependent electronic band structure. A controllable, reproducible uniaxial strain, ϵ, is applied to nanometer-thick GaSe layers via their bending on a mica substrate. The spectral shift ΔE of the room temperature photoluminescence emission corresponds to a strain coefficient ΔE/ϵ of up to ~100 eV, the largest value reported in the literature to date. This is accompanied by coupled electronic and vibrational states under strain-induced resonant excitation conditions, as probed by Raman spectroscopy.