NCAFM2023 Programme Booklet

SELECTIVE ENRICHING OF TRIONIC EMISSION IN A WS2-ZnO HYBRID THROUGH TYPE II BAND ALIGNMENT

Eng Tuan Poh 1* , Jin Feng Leong 3 , Kim Yong Lim 1 , Xiao Wu 2 , Qinghua Xu 2 , Chorng Haur Sow 1

1 Department of Physics, National University of Singapore, 117551 Singapore 2 Department of Chemistry, National University of Singapore, 117543 Singapore 3 Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore, 117583, Singapore

Email: phyetp@nus.edu.sg

Strategies to modulate the exciton dynamics in ultrathin two-dimensional (2D) semiconductor have always been an integral component in the bid towards improved optoelectronics and quantum photonic devices. The capability to non-destructively tune the relaxation dynamics, valley polarization, binding energies, and population ratio of various excitonic species has been well-sought for advanced applications. Through the rationale design of a WS 2 -ZnO hybrid platform, we present a distinct increment in the trion to exciton ratio for WS 2 emission across a patterned heterostructure. The shift in dominant excitonic species arose due to the efficient charge segregation at the spatially confined interface of the type-II heterostructure. Owing to the charge transfer process, the resultant emission profile presents up to four times amplification in the trion-to-exciton ratio, with temperature variable trion binding energies up to 59 meV. Since trions possess non-zero charge and spin degrees of freedom, the provision of a higher density of trions with increased binding stability would encourage new opportunities for reproducible optoelectronics and quantum emitters.

Fig. Design and characterization of WS 2 -ZnO heterostructure. (a) Schematic illustration of heterostructure design and intended optical phenomenon. Emplaced over differentiation regions comprising the SiO 2 substrate and ZnO fingers, the WS 2 monolayer is optically influenced by the underlying component – the monolayer region atop SiO 2 presents an exciton dominant emission, whereas the region atop the ZnO fingers is modified to emit with a greater trion ratio. (b) Optical micrograph showing the WS2-ZnO heterostructure assembled from transferring an exfoliated WS2 monolayer onto the ZnO fingers, along with the corresponding (c) fluorescence image and (d), (e) PL maps over the whole sample region. (d) The congruent PL map was established over the exciton emission range at (615 ± 5) nm. (e) The identical PL map was readjusted to show emission over the trion range at (628 ± 7) nm. The exact locations of the underlying ZnO fingers are marked out by the white dashed rectangles in (b)–(e). References References [1] J. F. Leong, K. Y. Lim, X. Wu, Q. Xu, C. H. Sow, E. T. Poh, Sci. China Inf. Sci., 2023, 66 (6), 160405, https://doi.org/10.1007/s11432-022-3719-4

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