Monitoring WSe₂ Monolayer Growth in Real Time Using In Situ Spectroscopic Ellipsometry

As demand for computing power increases, more and smaller transistors are required. In small field effect transistors (FETs), 2D films act as gates. At low thickness, traditional silicon semiconductors lose their advantageous electrical properties. WSe₂ and other transition metal dichalcogenides (TMDs) are optimal semiconductors for their low band gaps. The electronic properties of WSe₂ vary with the thickness of the material. A monolayer provides the preferable properties, but growing a single molecular layer of WSe₂ proves difficult. We grow our films on sapphire wafers using metal organic chemical vapor deposition (MOCVD). Spectroscopic ellipsometry (SE) allows for monitoring growth while it happens by taking spectra indicative of the optical constants of the material and its thickness. By constructing a model of WSe₂’s optical constants and applying it in situ, we confirmed that monolayer coverage can be fit and monitored in real time to end growth before a bilayer forms.