| Abstract [eng] |
Graphene, which has excellent electrical, optical, and thermal properties, is very attractive for applications in electronic and optoelectronic devices. Direct synthesis of graphene on silicon substrate by microwave plasma-enhanced chemical vapor deposition (PECVD) benefits in avoiding complex transfer procedures and is promising for industrial applications. However, such graphene often exhibits structural defects that have a significant impact on the performance of graphene field-effect transistors and junction devices. Low-frequency noise analysis is well-suited method for the quality evaluation of such structures and the investigation of charge carrier transport. So far, no scientific reports have been found in the literature on the characterization of graphene/h-BN/Si and hydrogenated graphene junctions using low-frequency noise spectroscopy. The aim of this work was to investigate the low-frequency noise characteristics of graphene grown by PECVD, junctions (graphene/h-BN/Si and hydrogenated graphene/Si), and field-effect transistors. The studied graphene/h-BN/Si and graphene/Si junctions were characterized by 1/f-type fluctuations, while in hydrogenated graphene/Si junctions, 1/f, Lorentzian, or both types of spectral densities were observed, depending on the ratio of H2 and CH4 gas flows used during the graphene synthesis. In the noise dependencies on the current for all graphene junctions, a rapid increase in noise intensity (~Iγ, γ > 2) was observed at high currents, which is associated with the influence of grain boundaries in graphene or h-BN layers and the effect of current crowding. In the case of hydrogenated graphene/Si junctions, an equivalent electrical circuit with noise sources was proposed to explain the unusual noise “bump” behaviour. It was demonstrated that hydrogen-related defects are a significant noise source in the investigated junctions. Statistical analysis of graphene/h-BN/Si junctions with (0 – 15) nm thickness h-BN interlayers revealed the highest noise intensity in junctions with a 5 nm h- BN interlayer. In order to determine the origin of the Lorentzian-type spectra in hydrogenated graphene/Si junctions, a temperature-dependent noise analysis was performed, which showed that the observed trap level with the activation energy of 0.4 eV is due to hydrogen or hydroxyl-related defects. Graphene field-effect transistors were characterized by 1/f-type electrical fluctuations, and at certain gate voltages, a random telegraph noise signal was observed. It was found that the unintentional n-type self-doping of the graphene due to interaction with the SiO2 layer has a significant impact on the investigated graphene transistors’ noise intensity. |
