Large area synthesis of GaSe and GaS monolayers by Chemical Vapor Deposition

Two-dimensional crystals of group-III metal monochalcogenides [i.e. MX where M={In, Ga} and X={S, Se,Te}] have gained attention in the last years as alternative 2D semiconductors. They present high carrier mobility, thickness dependent electronic properties, as well as good photoresponse and on/off ratio. To date, most of the fundamental studies in these materials have been performed on mechanically exfoliated samples and few groups have reported chemical vapor deposition (CVD) synthesis of these materials. The implementation of practical electronic applications will rely on developing approaches to deposit high quality films over large areas. The CVD approaches reported to date usually involve low pressure environment and MX powders with the right stoichiometry (pre-synthesized in vacuum sealed ampules) used as evaporation sources, as well as. Here we report large area deposition of GaSe and GaS monolayers, using atmospheric pressure CVD and commercially available precursors. We systematically studied the influence of the growth parameters on the quality of the as grown materials. The samples were characterized using micro-Raman spectroscopy, scanning electron microscopy and atomic force microscopy.