▎ 摘　　要

Recently, interband spectroscopic measurement of graphene Fermi level has been widely investigated because of its nondestructive and microcrack independent analysis. While successful in measuring the Fermi level, the optical methods suffer from one severe problem: spectral and spatial inhomogeneity of the substrates. In other words, the bare substrate transmissions, regarded as a reference transmission, are significantly different depending on the measurement position, whereby the estimated Fermi levels should be highly distorted. Here, we propose a new analytical expression to overcome the inhomogeneous substrate effects as well as to consider the multiple reflections in the finite substrate. We use the transmission at Dirac point as a reference signal instead of the bare substrate transmission, which enables to fix the sample position during the measurements and thereby free from the substrate effect. Based on our newly developed analytical expression, we measured the Fermi level of the chemical vapor deposition-grown graphene transferred on the SiO2/ Si substrate. Furthermore, the obtained Fermi levels with the optical measurement were continuous and symmetric in the whole measurement range while that with the electrical measurement exhibits unphysical Fermi level gap at the Dirac point due to the pinning effect at metal-graphene contact. (C) 2015 AIP Publishing LLC.