title: Enhanced Light Emission from Monolayer Semiconductors by Forming Heterostructures with ZnO Thin Films.
abstract: Monolayer transition-metal dichalcogenides (1L-TMDs) are atomically thin direct band gap semiconductors, from which the emission of light is determined by optical transitions of exciton complexes such as neutral excitons and trions. While the quantum yields of 1L-TMDs are quite low, the ability to control the populations of exciton complexes in 1L-TMDs through various doping processes is an interesting advantage, and provides ample possibilities for engineering the optical properties of these semiconductor monolayers. Here we demonstrate a simple method of controlling the populations of excitons and trions to enhance the light emission of 1L-TMDs by having them form heterostructures with ZnO thin films (TFs). 1Ls of MoS2or MoSe2showed up to 17-fold increases in photoluminescence (PL) when they were placed on ∼50 nm thick ZnO TFs. This enhancement of the PL was due to charge exchanges occurring through the 1L-TMD/ZnO interface. The PL enhancements and changes in the PL spectra of the 1L-TMDs were greater when the 1L-TMD/ZnO heterostructures were subjected to 355 nm wavelength laser excitation than when they were excited with a 514 nm wavelength laser, which we attributed to the onset of energy transfer by photoexcited excitons and/or the additional p-doping by photoexcited holes in ZnO. The p-doping phenomenon and the enhanced light emission of 1L-TMD/ZnO heterostructures were unambiguously visualized in spatially resolved PL and Raman spectral maps. Our approach using the 1L-TMD/ZnO TF heterostructure suggests that a rich variety of options for engineering the optical properties of 1L-TMDs may be made available by carrying out simple and intuitive manipulations of exciton complexes, and these endeavors may yield practical applications for 1L-TMDs in nanophotonic devices.
authors.affiliation: Center for Integrated Nanostructure Physics (CINAP), Institute for Basic Science (IBS) , Suwon 16419, Republic of Korea.|Sungkyunkwan University (SKKU) , Suwon 16419, Republic of Korea.
authors.forename: Min Su
authors.initials: MS
authors.lastname: Kim
authors.affiliation: Center for Integrated Nanostructure Physics (CINAP), Institute for Basic Science (IBS) , Suwon 16419, Republic of Korea.|Department of Energy Science, Sungkyunkwan University (SKKU) , Suwon 16419, Republic of Korea.
authors.forename: Shrawan
authors.initials: S
authors.lastname: Roy
authors.affiliation: Center for Integrated Nanostructure Physics (CINAP), Institute for Basic Science (IBS) , Suwon 16419, Republic of Korea.|Department of Energy Science, Sungkyunkwan University (SKKU) , Suwon 16419, Republic of Korea.
authors.forename: Jubok
authors.initials: J
authors.lastname: Lee
authors.affiliation: Department of Nanoscience & Engineering, Inje University , Gimhae 621-749, Republic of Korea.
authors.forename: Byung Gu
authors.initials: BG
authors.lastname: Kim
authors.affiliation: Center for Integrated Nanostructure Physics (CINAP), Institute for Basic Science (IBS) , Suwon 16419, Republic of Korea.|Department of Energy Science, Sungkyunkwan University (SKKU) , Suwon 16419, Republic of Korea.
authors.forename: Hyun
authors.initials: H
authors.lastname: Kim
authors.affiliation: Center for Integrated Nanostructure Physics (CINAP), Institute for Basic Science (IBS) , Suwon 16419, Republic of Korea.|Sungkyunkwan University (SKKU) , Suwon 16419, Republic of Korea.
authors.forename: Ji-Hoon
authors.initials: JH
authors.lastname: Park
authors.affiliation: Center for Integrated Nanostructure Physics (CINAP), Institute for Basic Science (IBS) , Suwon 16419, Republic of Korea.|Department of Energy Science, Sungkyunkwan University (SKKU) , Suwon 16419, Republic of Korea.
authors.forename: Seok Joon
authors.initials: SJ
authors.lastname: Yun
authors.affiliation: Center for Integrated Nanostructure Physics (CINAP), Institute for Basic Science (IBS) , Suwon 16419, Republic of Korea.|Sungkyunkwan University (SKKU) , Suwon 16419, Republic of Korea.
authors.forename: Gang Hee
authors.initials: GH
authors.lastname: Han
authors.affiliation: Department of Nanoscience & Engineering, Inje University , Gimhae 621-749, Republic of Korea.
authors.forename: Jae-Young
authors.initials: JY
authors.lastname: Leem
authors.affiliation: Center for Integrated Nanostructure Physics (CINAP), Institute for Basic Science (IBS) , Suwon 16419, Republic of Korea.|Department of Energy Science, Sungkyunkwan University (SKKU) , Suwon 16419, Republic of Korea.
authors.forename: Jeongyong
authors.initials: J
authors.lastname: Kim
keywords: 2D semiconductors; charge transfer; excitons; molybdenum diselenide; molybdenum disulfide; photoluminescence; tungsten diselenide