Investigating the Optical Properties of SnSe Films Using Spectroscopic Ellipsometry

SnSe films have been of particular interest because of their applications in piezoelectrics and optics. Using spectroscopic ellipsometry, we have measured the optical properties of SnSe films of a variety of thicknesses ranging from 4 nm to bulk. The SnSe thin films in the Pnma phase were grown using molecular-beam epitaxy and were deposited on (100) MgO substrates. After their growth, ellipsometry spectra were obtained on each film at three angles of incidence and in a spectral range between 0.5 eV and 3.5 eV. In modeling the ellipsometry spectra, we used the thicknesses determined by x-ray reflectivity. Initially, the dielectric functions were modeled using an isotropic model where two-oscillators were placed to represent the electronic transitions of SnSe. We find that in general, the absorption increases as the thickness of SnSe increases. In addition, the absorption peak seems to red-shift as the thickness increases. The dielectric functions obtained for the anisotropic models will also be presented.