ELLIPSOMETRY OF ANISOTROPIC SUBSTRATES - REEXAMINATION OF A SPECIAL CASE

When the index of refraction of a bulk material is determined using ellipsometry, an erroneous result is obtained if the material is anisotropic, and we have assumed that it is isotropic. This is not surprising. What is surprising is that, in the case of a uniaxial material with its optic axis perpendicular to the surface, the apparent index of refraction obtained from ellipsometric measurements does not lie between the ordinary and extraordinary indices of refraction and is therefore not even a good estimate of the actual index of refraction experienced by light in the anisotropic material. In addition, even though the actual index of refraction experienced by the light depends on the angle of incidence, making ellipsometric measurements at different angles of incidence does not resolve this problem.