title: Quantum size confinement in gallium selenide nanosheets: band gap tunability versus stability limitation.
abstract: Gallium selenide is one of the most promising candidates to extend the window of band gap values provided by existing two-dimensional semiconductors deep into the visible potentially reaching the ultraviolet. However, the tunability of its band gap by means of quantum confinement effects is still unknown, probably due to poor nanosheet stability. Here, we demonstrate that the optical band gap band of GaSe nanosheets can be tuned by ∼120 meV from bulk to 8 nm thick. The luminescent response of very thin nanosheets (<8 nm) is strongly quenched due to early oxidation. Oxidation favors the emergence of sharp material nanospikes at the surface attributable to strain relaxation. Simultaneously, incorporated oxygen progressively replaces selenium giving rise to Ga2O3,with a residual presence of Ga2Se3that tends to desorb. These results are relevant for the development and design of visible/ultraviolet electronics and optoelectronics with tunable functionalities based on atomically thin GaSe.
authors.affiliation: ICMUV, Instituto de Ciencia de Materiales, Universidad de Valencia, PO Box 22085, E-46071 Valencia, Spain.
authors.forename: Daniel
authors.initials: D
authors.lastname: Andres-Penares
authors.affiliation: ICMUV, Instituto de Ciencia de Materiales, Universidad de Valencia, PO Box 22085, E-46071 Valencia, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Cros
authors.affiliation: ICMUV, Instituto de Ciencia de Materiales, Universidad de Valencia, PO Box 22085, E-46071 Valencia, Spain.
authors.forename: Juan P
authors.initials: JP
authors.lastname: Martínez-Pastor
authors.affiliation: ICMUV, Instituto de Ciencia de Materiales, Universidad de Valencia, PO Box 22085, E-46071 Valencia, Spain.
authors.forename: Juan F
authors.initials: JF
authors.lastname: Sánchez-Royo