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, Cr 2 S 3 and Cr 2 Se 3 , are insufficient and most of them focus on individual crystal grains. In this study, large-scale Cr 2 S 3 and Cr 2 Se 3 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 Cr 2 S 3 and Cr 2 Se 3 films, including optical bandgap, activation energy and electrical properties, are measured with different thicknesses. The 1.9 nm thick Cr 2 S 3 and Cr 2 Se 3 films show narrow optical bandgap of 0.732 and 0.672 eV, respectively. The electrical properties of Cr 2 S 3 films demonstrate p -type semiconductor behaviours, while the Cr 2 Se 3 films exhibit no gate response. This work can provide a feasible method for growing large-scale Cr 2 S 3 and Cr 2 Se 3 films, and reveal fundamental information of their physical properties, which is helpful for future applications.