Raman and photoluminescence spectroscopy of a-C:H films deposited by microwave-assisted plasma CVD under D.C. bias and pulse bias

a-C:H films are deposited using microwave-assisted plasma CVD deposition under the influence of low-D.C. bias and high-pulse bias. Pulsed bias applied to the substrate results in higher growth rates compared to the D.C. bias. Microstructure of these films is studied using Raman and photoluminescence spectroscopy (PL) indicating different bonding configurations of sp2 clusters. The D-band, which is present in samples deposited under D.C. bias, is found to be absent in case of samples deposited under pulsed bias. This suggests presence of six-fold aromatic rings (benzene type) in films prepared under D.C. bias, which are absent in the later samples. Instead, these samples have distorted six-fold rings and/or olefinic chains. The PL spectra have been analyzed based on different bonding configurations of sp2 clusters forming defect states, recombination within which leads to sharp PL peaks. The intense PL peaks observed in the case of pulsed bias together with the missing D-band in their Raman spectra suggest abundance of distorted six-fold aromatic rings.