Electronic properties of PLD prepared nitrogenated a-SiC thin films

The electrical transport properties of a set of amorphous SiCxNy thin films have been investigated in the temperature range from 100 to 530 K. Information about the stoichiometry and the structural properties of the samples have been obtained by means of X-ray photoelectron spectroscopy, while the optical band gap was obtained by means of spectroscopic ellipsometric measurements. A widening of the optical band gap E-g from 1.6 eV up to 2.4 eV was observed as the nitrogen content of the samples increased up to 7.5%. Two distinct electrical conduction mechanisms were observed at high and low temperature, and attributed to the conduction in band, or band edge, states, and to activate nearest-neighbour hopping, respectively. The activation energy of the high temperature conduction mechanism was found to increase from approximately 0.2 eV up to 0.9 eV, increasing the nitrogen content, while the room temperature dark conductivity decreased from 10(-5) to 10(-9) Omega(-1) cm(-1). Such findings are compatible with a reduction of band gap states and a simultaneous widening of the gap itself, as a result of nitrogen incorporation, and was related to the increase of the Si-N over Si-Si bond number ratio as reported by the XPS analysis. (C) 2003 Elsevier Science B.V. All rights reserved.