Optical properties of alpha -SiC:H thin films grown by rf sputtering.

Abstract

In this work, the optical transmission and reflection of \ensuremath{\alpha}-SiC:H thin films, grown by rf sputtering, are studied. The absorption coefficient is found. The real (${\mathrm{\ensuremath{\varepsilon}}}_{1}$) and the imaginary (${\mathrm{\ensuremath{\varepsilon}}}_{2}$) part of the dielectric function are determined by means of ellipsometric measurements, in the region 1.5--6.3 eV. The dependence of ${\mathrm{\ensuremath{\varepsilon}}}_{1}$ and ${\mathrm{\ensuremath{\varepsilon}}}_{2}$ on substrate temperature and hydrogen flow rate is obtained. The experimental results are modeled using a theoretical formula for the dielectric function. rf ion etching and an in situ ellipsometric technique are used to check the influence of possible overlayers and establish realistic values of the dielectric function. The energy gaps of the films are found to be controlled by their content in hydrogen, increasing with hydrogen incorporation. Evidence that the incorporation of hydrogen induces the formation of voids, resulting in a density deficit in the front surface layers, is given. The maximum values ${\mathrm{\ensuremath{\varepsilon}}}_{2\mathrm{m}\mathrm{a}\mathrm{x}}$, found at approximately 5 eV, are reduced with the increase of the hydrogen flow rate, while increased substrate temperatures result in increased optical response. The formation of \ensuremath{\alpha}-Si or \ensuremath{\alpha}-C clusters in the film-substrate interface of the rf sputtered \ensuremath{\alpha}-SiC:H films is probed using back reflection techniques.