Growth of wafer-scale chromium sulphide and selenide semiconductor films.

Two-dimensional (2D) transition metal chalcogenides have attracted enormous attention due to their stunning properties and great prospects for applications. Most of the reported 2D materials have layered structure, and non-layered transition metal chalcogenides are rare. Particularly, chromium chalcogenides are highly complexed in terms of structural phases. Researches on their representative chalcogenides, Cr2S3 and Cr2Se3, are insufficient and most of them focus on individual crystal grains. In this study, large-scale Cr2S3 and Cr2Se3 films with controllable thickness are successfully grown, and their crystalline qualities are confirmed by multiple characterizations. Moreover, the thickness-dependent Raman vibrations are investigated systematically, presenting slight redshift with increasing thickness. The fundamental physical properties of grown Cr2S3 and Cr2Se3 films, including of optical bandgap, activation energy and electrical properties, are measured with different thicknesses. The 1.9 nm thick Cr2S3 and Cr2Se3 films show narrow optical bandgap of 0.732 and 0.672 eV, respectively. The electrical properties of Cr2S3 films demonstrate p-type semiconductor behaviours, while the Cr2Se3 films exhibit no gate response. This work can provide a feasible method for growing large-scale Cr2S3 and Cr2Se3 films, and reveal fundamental information of their physical properties, which is helpful for future applications.