Thickness-dependent Raman spectra of CVD-grown WSe₂ thin films

Tungsten diselenide (WSe₂) thin films with different thicknesses were fabricated on sapphire wafers. To fabricate centimeter-scale large-area films, we evaporated tungsten-oxide films followed by selenization under various hydrogen gas concentrations (0 - 20%) and at various substrate temperatures (700 - 1000 °C) in a chemical-vapor-deposition chamber. We utilized the Raman spectral intensity to evaluate the optimum growth conditions (15% and 875 °C) and observed a thickness-dependent change in the phonon peaks in the thickness range from 0.3 to 8 nm. By comparing the major peaks (E¹_2g, A_1g, and 2LA), we confirmed that the WSe₂ films had the expected film thicknesses and the corresponding peak shapes. Our results demonstrate both a growth method for the large-area WSe₂ films with thickness controllability and a nondestructive analysis method for determining the layer thickness over a wide thickness range.