Raman and photoluminescence study of magnetron sputtered amorphous carbon films

The structural and optical properties of amorphous carbon films, grown by r.f.-magnetron sputtering on silicon substrates, were studied by Raman and photoluminescence spectroscopy in dependence of the substrate bias voltage Vb. The intensity ratio I(D)/I(G) of the Raman bands of disordered graphite (D-band) and graphite (G-band) decreased significantly (a) by reversing bias from positive (+10 V) to negative (−20 V) and (b) by reducing the negative bias from −200 to −120 V. The intensity ratio I(D)/I(G) exhibited an almost flat minimum in the bias-region from −120 to −20 V which is indicative of an increase of the fraction of sp3-bonded material. In the same bias-range, photoluminescence emission at 2.2–2.5 eV appeared blue-shifted and more efficient. Changes in photoluminescence energy are attributed to increase of sp3 content of the films becoming more transparent when deposited at substrate-bias between −20 and −120 V. Increase of photoluminescence intensity is probably related to increased number of defects due to increasing structural disorder. [Copyright &y& Elsevier]