Hydrogenated Carbon Nitride Thin Films Deposited by the Plasma Chemical Vapor Deposition Technique Using Trimethylamine and Ammonia

Abstract

Hydrogenated carbon nitride ( C1-x Nx :H) thin films were successfully deposited on Si and quartz substrates by the rf plasma chemical vapor deposition (PCVD) technique. A gas mixture of trimethylamine ( (CH3)3N) and ammonia ( NH3) introduced to a reaction chamber as material gases was decomposed by glow discharge using an induction-coupled-type PCVD apparatus. The deposited films were characterized by X-ray photoelectron spectroscopy (XPS) and infrared (IR) absorption measurements. They are identified to be C1-x Nx :H without notable contamination during the deposition such as oxygen. The N1s XPS spectra strongly suggest that the nitrogen atoms are single-bonded covalently with carbon atoms via nitrogen sp2 and carbon sp3 orbitals for all trimethylamine flow rate ratios, and a C–N network grows with decreasing the trimethylamine flow rate ratio. The IR absorption spectra show that both pyridine-like sp2-hybridized carbon and sp-hybridized carbon atoms in cyano-radicals also increase as the trimethylamine flow rate ratio decreases. Since the N–C single bonds in trimethylamine are preserved during the plasma decomposition, a large number of nitrogen atoms are effectively incorporated and form single N–C bonds in the deposited films. The films are pale yellow and have an optical bandgap of 3 eV, estimated from the optical absorption spectra. The film exhibits a photoluminescence spectrum with a broad peak, which can be deconvoluted into two Gaussian curves with peak energies in the ranges of 2.2–2.4 and 2.8–3.1 eV. The higher-energy peak is regarded as band-edge luminescence from the single-bonded carbon nitride network.