Band alignment determination of bulk h-BN and graphene/h-BN laminates using photoelectron emission microscopy

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Abstract

Because graphene stacked on hexagonal boron nitride (h-BN) exhibits high electron mobility, it is expected to be applied to next-generation high-speed transistors and electron emitters. To further improve the performance of graphene/h-BN devices, it is necessary to determine the band alignment of graphene/h-BN laminates. However, because mechanically peeled h-BN single crystals transferred onto Si substrates are small, pinpoint observation of h-BN with ordinary photoelectron spectroscopy is difficult. In this study, the electric structure of a graphene/h-BN laminate was identified by photoemission electron microscopy and local measurements of valence band and secondary electron spectra using micro-ultraviolet photoelectron spectroscopy were performed. From these measurements, we determined the band alignment of a graphene/h-BN laminate with a crystal size of a few tens of micrometers. The work function and electron affinity measured by photoelectron spectroscopy of single-crystal h-BN were 4.6 and −0.5 eV, respectively. Laminating graphene on h-BN caused the Fermi level of h-BN to rise 0.85 eV above that of nonlaminated h-BN. In addition, it was found that graphene on h-BN displayed weak n-type conductivity. The results obtained in this research are expected to be widely applied in the field of electronics such as electron emitters using h-BN with negative electron affinity.

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Ogawa, S., Yamada, T., Kadowaki, R., Taniguchi, T., Abukawa, T., & Takakuwa, Y. (2019). Band alignment determination of bulk h-BN and graphene/h-BN laminates using photoelectron emission microscopy. Journal of Applied Physics, 125(14). https://doi.org/10.1063/1.5093430

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