Optical absorption and transport mechanisms of dual ion-beam-deposited boron-rich boron nitride films

The optical absorption and electrical conductivity of amorphous B-rich boro n nitride (BNx) films with N contents varying from 2.2 to 40.2 at.% were in vestigated. The density of states (DOS) of the films was extracted from the observed optical absorption spectra. All types of electron transitions fro m occupied initial states to empty final states were considered, including those between two localized states. Furthermore. a Gaussian-shaped energy b and of localized states was added to the center of the pseudo-gap in order to obtain good fits for most of the spectra. The major conclusions are as f ollows. (1) The activation energy deduced from the temperature dependence o f the electrical conductivity is low compared to the optical band gap. sugg esting that hopping of charge carriers near the Fermi level dominates the e lectrical transport properties of the films. (2) With increasing N content, the hopping distance of charge carriers increases and the spread of the el ectron wavefunction narrows. This leads to a more than seven orders of magn itude drop in the room temperature electrical conductivity. (C) 2001 Elsevi er Science B.V. All rights reserved.