Birefringent and Complex Dielectric Functions of Monolayer WSe2 Derived by Spectroscopic Ellipsometer

Because of its highly anisotropic confinement of its crystal structure, monolayer WSe2 should exhibit a birefringent optical property, i.e., the light of in-plane and vertical polarization will experience different velocity and loss when propagating in the vicinity of such a material. However, most research so far treats monolayer WSe2 as an isotropic material and ignores the important difference upon light–matter interaction at different polarizations. In this work, monolayer WSe2 is studied as a uniaxial crystal with different complex dielectric functions with respect to the in-plane and vertical polarization. The sample is measured by a spectroscopic ellipsometer, followed by a strict modeling process with a series of classic oscillators. The results show that the complex dielectric functions of monolayer WSe2 are clearly polarization-dependent. The obtained data are essential for the design of polarization-dependent integrated optoelectronic devices utilizing monolayer WSe2 as a key functional material.