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Potassium-doped hexagonal boron nitride (h-BN) was synthesized by electrochemical (EC) treatment in potassium hydroxide solution, and its electrical properties were measured. Back-gate field-effect transistors (FETs) of EC-treated h-BNs were fabricated using electron beam lithography and lift-off process. The drain current–gate voltage (ID–VG) characteristics showed that ID increased with VG, indicating n-type conduction. In contrast, the ID of pristine h-BN FETs was below the detection limit of the system. Results of advanced techniques such as annular dark-field scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and electron energy loss spectroscopy indicate that agglomerated potassium atoms are intercalated between h-BN layers. [ABSTRACT FROM AUTHOR]

To suppress the intrinsic carrier density and increase the carrier mobility in graphene on a silicon dioxide (SiO2) substrate, potassium (K)-doped nano graphene was introduced as an intermediate layer between the graphene layer and SiO2 substrate. Back-gate type graphene field effect transistors with four terminal structures were fabricated, and their electrical properties were measured under vacuum. The results showed that the Dirac point shifted from +9.0 to −0.2 V after inserting the K-doped nano graphene. The results suggested that inserting the intermediate layer compensated for the intrinsic holes and achieved an electron doping of 2 × 1012 cm−2. The field-effect mobilities of electrons and holes also increased because the ionized K-atoms in the intermediate layer shielded the electric force from the negatively charged impurities in SiO2. The K density was estimated using x-ray photoelectron spectroscopy to be 1.49 × 1013 cm−2, and the C1s peak shifted by 0.2 eV, which confirms the upward modulation of the graphene Fermi level by the K-doped nano graphene intermediate layer. These results demonstrated the advantages of the intermediate layer on the carrier density and mobility in graphene. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]