Influence of substrate bias on the properties of a-C:H films prepared by plasma CVD

Abstract

We have measured photoluminescence (PL) and Raman spectra for a series of amorphous carbon (a-C:H) films prepared in a RF-plasma CVD system. The negative bias voltage was varied between 0V and 950V. The samples seem to consist of two components. One polymeric component has a high band gap and gives strong luminesence above 2.1 eV with 0.6 eV band width. The second component shows the Raman spectrum that is typical for the sp2-clusters of hard carbon. We find that the hard carbon component seems to be absent for zero bias voltage. The PL for this sample, however, is strongest. We find a fatiguing of the luminescence during laser excitation. This fatiguing is weaker at 120 K, resulting in a higher PL-efficiency for this temperature. © 1993.