OPTICAL-PROPERTIES OF ALPHA-SIC-H THIN-FILMS GROWN BY RF-SPUTTERING

In this work, the optical transmission and reflection of alpha-SiC:H t hin films, grown by rf sputtering, arc studied. The absorption coeffic ient is found. The real (epsilon1) and the imaginary (epsilon2) part o f the dielectric function are determined by means of ellipsometric mea surements, in the region 1.5-6.3 eV. The dependence of epsilon1 and ep silon2 on substrate temperature and hydrogen flow rate is obtained. Th e experimental results are modeled using a theoretical formula for the dielectric function. rf ion etching and an in situ eilipsometric tech nique are used to check the influence of possible overlayers and estab lish realistic values of the dielectric function. The energy gaps of t he films are found to be controlled by their content in hydrogen, incr easing with hydrogen incorporation. Evidence that the incorporation of hydrogen induces the formation of voids, resulting in a density defic it in the front surface layers, is given. The maximum values epsilon2m ax, found at approximately 5 eV, are reduced with the increase of the hydrogen flow rate, while increased substrate temperatures result in i ncreased optical response. The formation of alpha-Si or alpha-C cluste rs in the film-substrate interface of the rf sputtered alpha-SiC:H fil ms is probed using back reflection techniques.