Investigation of low-frequency noise in van der Waals epitaxies

We report the growth of high quality SnS van der Waals epitaxies (vdWEs) on mica by molecular beam epitaxy (MBE). Record low rocking curve FWHM for the SnS (001) and SnSe (001) epilayers were observed. Detailed investigations of the film morphology indicate layer-by-layer growth mode expected for 2D layered structure. The characteristic structural symmetry of the mica surface leads to the nucleation of crystallites with different lateral orientations. This results in high concentration of grain boundaries and high level of low-frequency excess noise. We investigated the growth mechanisms of the vdWEs and suggested a novel growth technique in which a SnSe buffer layer is utilized to reduce the concentration of the grain boundary. The idea is tested experimentally and significant reduction in the low-frequency noise is observed suggesting the use of the buffer layer had resulted in the reduction in the possible growth orientations of the top SnS epilayer and thereby reducing the grain boundary concentration.