RADIATIVE RECOMBINATION PROCESSES AND DEFECTS IN A-C-H FILMS DEPOSITED BY PECVD

The aim of this work is to present a consistent picture of the electro nic density of states (DOS) close to the Fermi energy level in a-C:H m aterials and to clarify its correlation with photoluminescence process es. When the sp(2) sites fraction is below a percolation threshold, th e DOS bands due to pi and pi states, energetically located between th e sigma and sigma bands, are localized. The one-electron approximatio n can be used to describe the optical transitions only if such localiz ed nature of the DOS is considered. Four types of electronic states re sponsible for non-radiative recombinations are assumed to be present i n the energy region near Fermi level: states occupied by pi paired ele ctrons, pi states of sp(2) isolated sites, sigma dangling bonds and pi states due to sp(2) odd clusters. In the light of this DOS model, a s uccessful correlation between photoluminescence quantum efficiency and electronic DOS abundance near Fermi level has been reached. (C) 1998 Elsevier Science S.A.