Ion beam effects on the hydrogenated bonds of amorphous silicon carbide

Ion irradiation of amorphous hydrogenated silicon carbide films introduces additional disorder into the films and leads to chemical modifications. These effects were monitored using Infrared, UV-visible optical and Raman spectroscopies. Samples were prepared by plasma enhanced chemical vapour deposition (PECVD), then irradiated with 300 keV Ar(+) to fluences ranging from 5 x 10(13) to 1 x 10(15) cm(-2). The hydrogen concentration was determined by elastic recoil detection analysis using 2.0 MeV He(+) beam. After ion irradiation, the absorption coefficient in the UV-visible energy range was observed to increase by an order of magnitude, while the optical energy gay decreases from 3.2 eV to 2.0 eV. These changes are due to the formation of carbon clusters, as evidenced by the carbon yield in Raman measurements. Infrared spectra indicate that this excess of carbon atoms results from the breaking of CH, bonds in the as-grown film and by a concomitant decrease in the hydrogen concentration. In addition, defects created by ion bombardment change the oscillator strength of the Si-H vibrational modes. (C) 2000 Elsevier Science B.V. All rights reserved.