Synthesis of Large-Area GeS Thin Films with the Assistance of Pre- deposited Amorphous Nanostructured GeS Films: Implications for Electronic and Optoelectronic Applications

Germanium monosulfide as a layered material analogous to black phosphorus has recently been synthesized in layers up to several square micrometers in area using a physical vapor transport process. However, single-crystalline GeS tends to be sparsely, haphazardly, and discretely nucleated on the target substrate. This phenomenon has hitherto impeded the development of applications since it limits the obtainable size of crystalline GeS films. In this study, we investigate a different heating recipe for synthesizing continuous large-area GeS without the use of metal catalysts. By laying down a pre-deposited amorphous nanostructured GeS film, a polycrystalline GeS film of the order of square centimeters can be attained using a purpose-built vapor transport equipment. This growth process can be used to fabricate a continuous polycrystalline GeS film (1 cm x 1.5 cm) on different substrates such as SiO2/Si or mica. The observed minimum thickness of polycrystalline GeS films is around 100 nm. Large-area GeS films synthesized on a mica substrate can also be easily exfoliated and transferred onto chosen substrates, giving them significant potential for use in next-generation electronic and optoelectronic applications. This method may also be useful for synthesizing other large-area chalcogenide materials.