PHOTOLUMINESCENCE STUDIES OF HYDROGENATED AMORPHOUS-CARBON AND ITS ALLOYS

In this article, we have studied the photoluminescence (PL) behaviors of a-C:H and its alloys (a-C:H,N,F). The samples were deposited in a r adio frequency plasma enhanced chemical vapor deposition system with v arious mixtures of CH4, N-2, and NF3 gases. For this work, the effects of doping and excitation energy on PL peak position and bandwidth wer e investigated in detail. It was found that with the decrease in Tauc gap, the PL peak shifts to lower energy and the bandwidth is narrowed. If the excitation energy is below a certain energy, the PL peak shift s to lower energy and the bandwidth is reduced through a cutoff of the high energy region. If the excitation energy is above a certain energ y, the PL becomes saturated and the shape remains almost the same. Our results support the cluster model proposed by Robertson that a-C:H co ntains both sp(2) and sp(3) sites, with sp(2) clusters embedded in a s p(3) bonded matrix. Our PL data are explained by the distribution func tion of cluster gaps. (C) 1997 American Institute of Physics. [S0021-8 979(97)05521-7].