Probing the band structure of hydrogen-free amorphous carbon and the effect of nitrogen incorporation

Amorphous carbon and carbon nitride bottom gate thin film transistors have been fabricated, which show bulk carrier field effect mobilities around 10(-3) (cm(2) V-1 s(-1)) which is orders of magnitude higher than the previously reported values with p-channel devices at high electric fields between source and drain. The incorporation of nitrogen atoms into the amorphous carbon films deposited by pulsed laser deposition was studied using a wide range of techniques in order to understand the role of nitrogen in the conduction mechanism at high fields. The density of the states (DOS) was measured with several techniques such as electron energy loss spectroscopy, scanning tunnelling spectroscopy, and ultraviolet photoelectron spectroscopy, whereas the joint density of states (JDOS), corresponding to the transitions of electrons from the valence to the conduction bands, were obtained by optical transmittance and photothermal deflection spectroscopy. These measurements when combined can provide unparallel data on the shape and magnitude of the energy band states which are crucial to the understanding of the materials properties and thus opto-electronic applications for these thin films. In this report, the conduction mechanism will be discussed with a band diagram drawn based on the experimentally obtained DOS and JDOS measurements. (C) 2011 Elsevier Ltd. All rights reserved.