Comparison of CPM, PDS and Optical Transmittance of Amorphous Carbon Nitride Films Made by a Nitrogen Radical Sputter Method

Abstract

ABSTRACTAmorphous carbon nitride films a-CNX, deposited in our laboratory by a radical sputter method, show high photosensitivity PS, where PS is the ratio of photoconductivity sP and dark-electrical conductivity sd. A-CNX made a layer-by-layer method, LLa-CNX, has the highest photosensitivity in our various preparation conditions. The photoconductivity in a-CNX and LLa-CNX shows dependence on photon energy in the range 2 eV to 6.2 eV. The constant photocurrent method (CPM), photothermal deflection spectroscopy (PDS) and optical transmittance spectra are used to obtain the information in the optical energy band gap and defect states. A-CNX and LLa-CNX are good photoconductors especially at energy higher than 3 eV. Therefore it is not difficult to obtain CPM spectra in the high photon energy region. CPM spectra are obtained by dc- and ac- measurements. The value of the absorption coefficient a spectra obtained by dc-CPM is larger than that of ac-CPM, which increases with increasing frequency of the measurement. In this paper, CPM data is used to discuss a model of density of states (DOS) of a-CNX by comparison with PDS and optical transmittance spectra.