Youngsup Park
Kyung Hee University, Seoul, South Korea
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We have investigated the transport and optical gap of hexagonal boron nitride (hBN) using the combination of UV photoelectron spectroscopy (UPS), inverse photoelectron spectroscopy (IPES), and reflection electron energy loss spectroscopy (REELS). Despite its importance in hBN, the experimental measurements of the transport band gap of hBN remains unclear, primarily due to challenges in synthesizing large-area sheets and its inherent insulating characteristics. To address this, we measured the transport gap of single layer of hBN synthesized on different large conducting substrates such as copper, gold and ITO by using UPS and IPES. By correlating experimental spectra with the density of states calculated using the GW approximation, and combining with REELS measurements of optical gaps, we could infer concrete values of exciton binding energies for these samples. We found that the transport gap is roughly in agreement with calculated values reported previously, while the exciton binding energy is over 1 eV for single layer sample. Furthermore, the difference in the transport gap observed among different substrates is mainly due to the reduction in exciton binding energy resulting from enhanced screening by the metal. We discuss the possible origins of these dependences.
Email: parky@khu.ac.kr