  Few-layer GaSe is one of the latest additions to the family of 2D
semiconducting crystals whose properties under strain are still relatively
unexplored. Here, we study rippled nanosheets that exhibit a periodic
compressive and tensile strain of up to 5%. The strain profile modifies the
local optoelectronic properties of the alternating compressive and tensile
regions, which translates into a remarkable shift of the optical absorption
band-edge of up to 1.2 eV between crests and valleys. Our experimental
observations are supported by theoretical results from density functional
theory calculations performed for monolayers and multilayers (up to 7 layers)
under tensile and compressive strain. This large band gap tunability can be
explained through a combined analysis of the elastic response of Ga atoms to
strain and the symmetry of the wave functions.
