Junyong Wang

@article{ISI:001205711600001,
title = {Upconversion electroluminescence in 2D semiconductors integrated with plasmonic tunnel junctions},
author = {Zhe Wang and Vijith Kalathingal and Maxim Trushin and Jiawei Liu and Junyong Wang and Yongxin Guo and Barbaros Ozyilmaz and Christian A Nijhuis and Goki Eda},
doi = {10.1038/s41565-024-01650-0},
times_cited = {4},
issn = {1748-3387},
year = {2024},
date = {2024-04-19},
journal = {NATURE NANOTECHNOLOGY},
volume = {19},
number = {7},
publisher = {NATURE PORTFOLIO},
address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY},
abstract = {Plasmonic tunnel junctions are a unique electroluminescent system in which light emission occurs via an interplay between tunnelling electrons and plasmonic fields instead of electron-hole recombination as in conventional light-emitting diodes. It was previously shown that placing luminescent molecules in the tunneling pathway of nanoscopic tunnel junctions results in peculiar upconversion electroluminescence where the energy of emitted photons exceeds that of excitation electrons. Here we report the observation of upconversion electroluminescence in macroscopic van der Waals plasmonic tunnel junctions comprising gold and few-layer graphene electrodes separated by a similar to 2-nm-thick hexagonal boron nitride tunnel barrier and a monolayer semiconductor. We find that the semiconductor ground exciton emission is triggered at excitation electron energies lower than the semiconductor optical gap. Interestingly, this upconversion is reached in devices operating at a low conductance (<10(-6) S) and low power density regime (<10(2) W cm(-2)), defying explanation through existing proposed mechanisms. By examining the scaling relationship between plasmonic and excitonic emission intensities, we elucidate the role of inelastic electron tunnelling dipoles that induce optically forbidden transitions in the few-layer graphene electrode and ultrafast hot carrier transfer across the van der Waals interface.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:001133459300001,
title = {Optical Gain Spectrum and Confinement Factor of a Monolayer Semiconductor in an Ultrahigh-Quality Cavity},
author = {Tianhua Ren and Junyong Wang and Kaizhen Han and Yuye Kang and Annie Kumar and Gong Zhang and Zhe Wang and Rupert F Oulton and Goki Eda and Xiao Gong},
doi = {10.1021/acs.nanolett.3c03357},
times_cited = {0},
issn = {1530-6984},
year = {2023},
date = {2023-12-08},
journal = {NANO LETTERS},
volume = {23},
number = {24},
pages = {11601-11607},
publisher = {AMER CHEMICAL SOC},
address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA},
abstract = {Two-dimensional (2D) semiconductors have attracted great attention as a novel class of gain materials for low-threshold, on-chip coherent light sources. Despite several experimental reports on lasing, the underlying gain mechanism of 2D materials remains elusive due to a lack of key information, including modal gain and the confinement factor. Here, we demonstrate a novel approach to directly determine the absorption coefficient of monolayer WS2 by characterizing the whispering gallery modes in a van der Waals microdisk cavity. By exploiting the cavity's high intrinsic quality factor of 2.5 x 10(4), the absorption coefficient spectrum and confinement factor are experimentally resolved with unprecedented accuracy. The excitonic gain reduces the WS2 absorption coefficient by 2 x 10(4) cm(-1) at room temperature, and the experimental confinement factor is found to agree with the theoretical prediction. These results are essential for unveiling the gain mechanism in emergent, low-threshold 2D-semiconductor-based laser devices.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}