Red-to-Ultraviolet Emission Tuning of Two-Dimensional Gallium Sulfide/Selenide

Abstract

Graphene-like two-dimensional (2D) nanostructures have attracted significant attention because of their unique quantum confinement effect at the 2D limit. Multilayer nanosheets of GaS–GaSe alloy are found to have a band gap (<i>E</i>_g) of 2.0–2.5 eV that linearly tunes the emission in red-to-green. However, the epitaxial growth of monolayers produces a drastic increase in this <i>E</i>_g to 3.3–3.4 eV, which blue-shifts the emission to the UV region. First-principles calculations predict that the <i>E</i>_g of these GaS and GaSe monolayers should be 3.325 and 3.001 eV, respectively. As the number of layers is increased to three, both the direct/indirect <i>E</i>_g decrease significantly; the indirect <i>E</i>_g approaches that of the multilayers. Oxygen adsorption can cause the direct/indirect <i>E</i>_g of GaS to converge, resulting in monolayers with a strong emission. This wide <i>E</i>_g tuning over the visible-to-UV range could provide an insight for the realization of full-colored flexible and transparent light emitters and displays