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 V-b. The intensity ratio I(D)l 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 sp(3)-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 sp(3) 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. (C) 2002 Elsevier Science B.V. All rights reserved.