Optical properties of GeOx films obtained by laser deposition and dc sputtering in a reactive atmosphere

Optical constants of amorphous GeOx films as a function of wavelength are determined for the first time, to the best of our knowledge, in thin films grown by laser deposition and dc sputtering of Ge in an oxygen environment. We determined the oxygen content of the films by combining nuclear reaction analysis and Rutherford backscattering spectrometry. Spectroscopic ellipsometry is used to determine the film optical constants. Effective medium modeling is used to simulate the optical properties of the films assuming the films contain a mixture of amorphous Ge and GeO2. The results show that substoichiometric GeOx films behave optically as a mixture of amorphous Ge and GeO2. Films with low oxygen content (x < 1.0) seem to have inhomogeneous oxygen concentrations with depth. The effect of the deposition rate and oxygen pressure (and Ar pressure in sputtered films) on film stoichiometry and optical properties is also discussed.