Very thin germanium films: optical and structural properties

Very thin and ultrathin optically isotropic layers are key components for many applications in X-ray optics, microelectronics and optical storage of the information. Here we present an application of a recently developed spectrophotometric method for determination of optical constants (refractive index, n, extinction coefficient, k, and physical thickness, d) of very thin films to thermally deposited germanium (Ge) films with d between 10 and 25 nm.. The method is based on limited development of the Abeles characteristic matrix elements. (n, k, d) are obtained by analytical solution of the system (1+R-f)/T-f, (1-R-f)/T-f and (1-R-f)/T-f, where (T-f) is the film transmittance, (R-f) is the front side and (R-f) backside reflectance. For comparison to the so-obtained (n, k, d), Veritable Angle Spectroscopic Ellipsometry is used as an independent technique. The ellipsometric angles are fitted, using a generalized oscillation layer. An acceptable relative difference between (n, k, d), obtained by both methods, is achieved.