Cw. Ong et al., Optical absorption and transport mechanisms of dual ion-beam-deposited boron-rich boron nitride films, THIN SOL FI, 388(1-2), 2001, pp. 217-225
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.