Modification of electrical characteristics of CVD- graphene by Joule heating

Abstract

This paper presents an approach for enhancing the electrical characteristics of graphene synthesized by chemical vapor deposition (CVD), through a direct resistive heating of the graphene channel by an electric current. This method efficiently purifies graphene of impurities and restores the material ideal structure through the desorption of adsorbed molecules. A graphene field-effect transistor was employed to characterize the graphene, specifically - to assess the mobility and concentration of charge carriers. The study investigates the impact of annealing temperature on both the concentration and type of charge carriers. It was found that CVD-synthesized graphene exhibits p-type conductivity, with the charge neutrality point (CNP) positioned above 80 Volts gate voltage at a 300 nm thickness of SiO₂. Annealing at 200 °C shifted this neutrality point to 0 Volts, switching the graphene to electrical neutrality. At higher annealing temperatures, n-type conductivity was achieved. Additionally, during the annealing process with current flow, there was a significant enhancement of the charge carriers mobility in graphene: for holes, mobility increased from 1000 cm²/(V·s) to 1800 cm²/(V·s), and for electrons - from 600 cm²/(V·s) to 1200 cm²/(V·s). Thus, the study reveals the effective method for removing impurities appeared after transfer of CVD graphene from copper foil to a dielectric substrate. This approach may be utilized in preparing samples for applications in microelectronics, optoelectronics, and related fields.