Photoluminescence studies of DC plasma CVD grown a-C : H : N films

Amorphous hydrogenated carbon films with different nitrogen contents (a-C:H :N) were deposited by DC plasma chemical vapour deposition of acetylene + n itrogen (0-62, vol.%) onto glass/Si/fused silica substrates. The deposition temperature was similar to 523 K at a system pressure of similar to 0.2 mb ar and negative bias voltage of -500 V. Photoluminescence of the a-C:H:N fi lms were studied with different excitation energies (E-ex) below and above the bandgap. The optical parameters (absorption coefficient, band gap and r efractive index) of a-C : H : N films were determined from the transmittanc e and ellipsometric measurements. Optical properties of the films could be explained by a two phase model which considers the existence of sp(2) clust ers (lower band gap region) embedded in a sp(3) matrix (higher band gap reg ion). Carrier confinement within the sp2 clusters gives rise to radiative r ecombination, producing strong photoluminescence (PL) at room temperature. The film quality was ascertained from the FTIR and Raman measurements. (C) 1999 Elsevier Science S.A. All rights reserved.