Abstract
Capacitance voltage (CV) measurements are performed on planar MOS capacitors with an Al2O3 dielectric fabricated in hydrogen intercalated monolayer and bilayer graphene grown on 6H-SiC as a function of frequency and temperature. Quantitative models of the CV data are presented in conjunction with the measurements in order to facilitate a physical understanding of graphene MOS systems. An interface state density of order 2 ⋅ 1012 eV−1 cm−2 is found in both material systems. Surface potential fluctuations of order 80-90meV are also assessed in the context of measured data. In bilayer material, a narrow bandgap of 260meV is observed consequent to the spontaneous polarization in the substrate. Supporting measurements of material anisotropy and temperature dependent hysteresis are also presented in the context of the CV data and provide valuable insight into measured and modeled data. The methods outlined in this work should be applicable to most graphene MOS systems.
Highlights
The electron transport properties of graphene monolayers and bilayers have generated significant amount of interest and competitive high speed field effect devices have been demonstrated in both materials.[1,2] Intercalated monolayers and bilayers grown by epitaxy on SiC are promising as they routinely demonstrate the excellent transport properties and material uniformity required for the fabrication of microwave integrated circuits.[3,4] field effect devices in graphene often demonstrate poor current modulation which significantly compromises high frequency performance.[5,6,7] In metal-oxide-semiconductor (MOS) systems, current modulation is strongly affected by dielectric quality and charge trapping effects
It is possible to estimate the density of interface states Dit, the magnitude of surface potential fluctuations δε f, the effect of material anisotropy, and the presence of a narrow energy gap ε g in bilayer material
The density of interface states is significant in both materials, and values of order 2 · 1012 eV−1cm−2 are extracted from measurement data
Summary
The electron transport properties of graphene monolayers and bilayers have generated significant amount of interest and competitive high speed field effect devices have been demonstrated in both materials.[1,2] Intercalated monolayers and bilayers grown by epitaxy on SiC are promising as they routinely demonstrate the excellent transport properties and material uniformity required for the fabrication of microwave integrated circuits.[3,4] field effect devices in graphene often demonstrate poor current modulation which significantly compromises high frequency performance.[5,6,7] In metal-oxide-semiconductor (MOS) systems, current modulation is strongly affected by dielectric quality and charge trapping effects. Graphene devices are sensitive to dielectric charging and interface trapping effects as they can screen current modulation This trade-off between exceptional material properties and non-ideal dielectrics warrant an investigation of charge control in metal-oxide-graphene systems
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