Electronic Structure, Surface Doping, and Optical Response in Epitaxial WSe2 Thin Films

Title
Electronic Structure, Surface Doping, and Optical Response in Epitaxial WSe2 Thin Films
Authors
류혜진Yi ZhangMiguel M. UgedaChenhao JinSu-Fei ShiAaron J. BradleyAna Martin-RecioJonghwan KimShujie TangYeongkwan KimBo ZhouChoongyu HwangYulin ChenFeng WangMichael F. CrommieZahid HussainZhi-Xun ShenSung-Kwan Mo
Issue Date
2016-04
Publisher
Nano letters
Citation
VOL 16, NO 4-2491
Abstract
High quality WSe2 films have been grown on bilayer graphene (BLG) with layer-by-layer control of thickness using molecular beam epitaxy. The combination of angle-resolved photoemission, scanning tunneling microscopy/spectroscopy, and optical absorption measurements reveal the atomic and electronic structures evolution and optical response of WSe2/BLG. We observe that a bilayer of WSe2 is a direct bandgap semiconductor, when integrated in a BLG-based heterostructure, thus shifting the direct-indirect band gap crossover to trilayer WSe2. In the monolayer limit, WSe2 shows a spin-splitting of 475 meV in the valence band at the K point, the largest value observed among all the MX2 (M = Mo, W; X = S, Se) materials. The exciton binding energy of monolayer-WSe2/BLG is found to be 0.21 eV, a value that is orders of magnitude larger than that of conventional three-dimensional semiconductors, yet small as compared to other two-dimensional transition metal dichalcogennides (TMDCs) semiconductors. Finally, our finding regarding the overall modification of the electronic structure by an alkali metal surface electron doping opens a route to further control the electronic properties of TMDCs.
URI
http://pubs.kist.re.kr/handle/201004/70279
ISSN
1530-6984
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