High quality SnS van der Waals epitaxies on graphene buffer layer

We report investigation of SnS van der Waals epitaxies (vdWEs) grown by molecular beam epitaxy (MBE) technique. Experimental results demonstrate an indirect bandgap of ~1 eV and a direct bandgap of ~1.25 eV. Substantial improvement in the crystallinity for the SnS thin films is accomplished by using graphene as the buffer layer. Using this novel growth technique we observed significant lowering in the rocking curve FWHM of the SnS films. Crystallite size in the range of 2-3 μm is observed which represents a significant improvement over the existing results. The absorption coefficient, α, is found to be of the order of 104 cm-1 which demonstrates sharp cutoff as a function of energy for films grown using graphene buffer layers indicating low concentration of localized states in the bandgap. Hole mobility as high as 81 cm2V-1s-1 is observed for SnS films on graphene/GaAs(100) substrates. The improvements in the physical properties of the films are attributed to the unique layered structure and chemically saturated bonds at the SnS/graphene interface. As a result, the interaction between the SnS thin films and the graphene buffer layer is dominated by a weak vdW force and structural defects at the interface, such as dangling bonds or dislocations, are substantially reduced.