Nanostructured Carbon Films Obtained by CH4 Plasma Deposition and Annealing at High Temperatures: Structural Features and Their Influence on the Electrical and Optoelectronic Properties

The structure and electrical and optoelectronic properties of nanostructured carbon films obtained by methane plasma deposition with subsequent annealing have been studied. It is shown that the film formation conditions affect the final physicochemical parameters. The film morphology has been investigated by atomic force microscopy, scanning electron microscopy, Raman spectroscopy, X-ray energy-dispersive analysis, and analysis of the current–voltage characteristics (CVCs). The film thicknesses range from 20 to 150 nm at the carbon-to-oxygen (C/O) atomic ratio of 4 : 1. Structural studies show that the films obtained consist of nanographite flakes with the lateral dimensions in the range from 5 to 12 nm and contain different fractional concentrations of sp 3 / sp 2 crystalline phases of carbon. It is established that the structural quality of carbon films decreases with an increase in the annealing temperature from 650°C to 800°C. At the same time, the degree of graphitization increases, which is indicated by Raman spectroscopy data and sheet resistances calculated from the CVCs. Photocurrents are calculated from the temperature dependences of the CVCs; it is found that the samples exhibit photosensitivity in the temperature range from room temperature to –173°C. These results may be useful for designing day and night light sensors and temperature sensors operating in a wide temperature range.