Controlled direct growth of Al2O3-doped HfO2 films on graphene by H2O-based atomic layer deposition

Abstract

Graphene has been drawing worldwide attention since its discovery in 2004. In order to realize graphene-based devices, thin, uniform-coverage and pinhole-free dielectric films with high permittivity on top of graphene are required. Here we report the direct growth of Al₂O₃-doped HfO₂ films onto graphene by H₂O-based atom layer deposition (ALD). Al₂O₃-onto-HfO₂ stacks benefited the doping of Al₂O₃ into HfO₂ matrices more than HfO₂-onto-Al₂O₃ stacks did due to the micro-molecular property of Al₂O₃ and the high chemical activity of trimethylaluminum (TMA). Al₂O₃ acted as a network modifier, maintained the amorphous structure of the film even to 800 °C, and made the film smooth with a root mean square (RMS) roughness of 0.8 nm, comparable to the surface of pristine graphene. The capacitance and the relative permittivity of Al₂O₃-onto-HfO₂ stacks were up to 1.18 μF cm⁻² and 12, respectively, indicating the high quality of Al₂O₃-doped HfO₂ films on graphene. Moreover, the growth process of Al₂O₃-doped HfO₂ films introduced no detective defects into graphene confirmed by Raman measurements.