Optical Constants of Silicon by Unpolarized Incident Radiation

It is shown that the reflectance of modulated unpolarized incident radiation at the pseudo-polarizing angle can be used to accurately determine the optical constants of absorbing media in the visible region. The approximation that the principal angle of incidence occurs at the pseudo-polarizing angle is assumed to contribute negligible error. Expressions for the refractive index, n, and the extinction coefficient, K, are given in terms of the pseudo-polarizing angle and the reflectance ratio of the parallel (to the plane of incidence) reflected wave vector intensity to the normal reflected wave vector intensity. The experimental values for n and K are determined at wavelengths in the visible spectrum between 4250 and 5750Å, for boron-doped p-type highly polished silicon of 0.01 and 95 Ω-cm resistivity. These values correspond to impurity concentrations of about 10^-3-10^-6%, respectively. The 0.01 Ω-cm K curve indicates the possibility that direct optical transitions between acceptor levels and the conduction band can be resolved and that this occurs at about 5250Å (≃2.4eV).