P.C. Patra and Y.N. Mohapatra
Indian Institute of Technology Kanpur,
Keywords: Thin Film, Photoluminescence, Dielectric Constant
Summary:Polymeric graphitic carbon nitride (g-C3N4) is a two dimensional (2D) wide band gap semiconductor in the blue region of the visible spectrum, tipped to be widely used as a photocatalyst for hydrogen production from water under visible light irradiation. However, currently the current studies are largely confined to g-C3N4 powder. To enable a larger gamut of optoelectronic applications, including UV sensors and emitters, it is necessary to focus on the thin film of the material. We report suitability of thin film of g-C3N4 by depositing it by thermal evaporation of the respective powder which in turn was synthesized from thermal condensation of melamine heating at 600C in a furnace for 4 hour. The optical properties of the g-C3N4 thin film are characterized through steady state photoluminescence (PL) and time resolved photoluminescence (TRPL) spectroscopy. The room temperature PL spectroscopy shows an asymmetric broad peak which is deconvoluted into three Gaussian peaks and hence to study their origin. The TRPL spectroscopy of the g-C3N4 thin film show a double exponential decay like that of bulk indicating the crystalline structure of the film. The surface morphology of the g-C3N4 thin film is characterized by Atomic Force Microscopy (AFM). We fabricate a simple device whose structure is Au/g-C3N4/Al, where each layer is deposited through evaporation in vacuum to study the nature of the g-C3N4 thin film. The roughness of 90 nm films is less than 4.2 nm and shows a low leakage current. The electrical dielectric constant of the film is found to be for the first time to be 4.06 till 10 KHz. We show that the thin film are suitable for device applications with dielectric constant comparable to organic polymers and yet has properties of a wide bandgap semiconductor.