Universal conformal ultrathin dielectrics on epitaxial graphene enabled by a graphene oxide seed layer

Abstract

The amphiphilic nature of graphene oxide (GO) is exploited as a seed layer to facilitate the ultrathin and conformal high-κ metal oxide (MOX) deposition on defect-free epitaxial graphene (EG) by atomic layer deposition (ALD). Three different high-κ metal oxides (Al2O3, HfO2 and TiO2) with various thicknesses (4–20 nm) were grown on ultrathin (1.5 nm) GO seed layers on EG. The quality of such dielectrics was examined by fabricating various metal-insulator-graphene (MIG) type devices. For MIG tunnel devices, on-off ratios of 104 and 103 were obtained for 4 nm Al2O3 and HfO2 dielectric layers, respectively. Additionally, no defect/trap assisted conduction behavior was observed. Graphene field effect transistors (GFETs) with bi-layer metal oxide stack (6 nm TiO2/14 nm HfO2) demonstrated a peak on-state current of 0.16 A/mm, an on-resistance of 6.8 Ω mm, an Ion/Ioff ratio of ∼4, and a gate leakage current below 10 pA/mm at Vds = 1 V and Vgs = 4 V. Capacitance-voltage measurement of the same GFETs exhibited a low hysteresis and nearly ideal dielectric constants. These results demonstrate a simple yet cost-effective universal way of wafer-scale ultrathin high-κ dielectrics deposition on epitaxial graphene by ALD.