Density of electronic states in amorphous carbons

In this paper we deal with the origin and features of the density of electronic states in the various types of a-C and a-C:H films. In particular we discuss the effects of disorder, distortions and composition (i.e. hydrogen and sp(2) carbon fractions) on the density of states and the main optoelectronic properties. We show that the wide differences among the various amorphous carbons can be understood by introducing three characteristic lengths of the structure (i.e. distance between neighbouring clusters, decay length of pi states and 'accommodation length' of sp(2) clusters in the sp(3) network). Finally, we discuss additional features crucial in determining film properties, such as the correlation energy. (C) 2003 Elsevier Science B.V. All rights reserved.