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Inserting hexagonal boron nitride (hBN) as barrier layers into bilayer transition metal dichalcogenides heterointerface has been proved an efficient method to improve two dimensional tunneling optoelectronic device performance. Nevertheless, the physical picture of interlayer coupling effect during incorporation of monolayer (1L-) hBN is not explicit yet. In this article, spectroscopic ellipsometry was used to experimentally obtain the broadband excitonic and critical point properties of WS2/MoS2 and WS2/hBN/MoS2 van der Waals heterostructures. We find that 1L-hBN can only slightly block the interlayer electron transfer from WS2 layer to MoS2 layer. Moreover, insertion of 1L-hBN weakens the interlayer coupling effect by releasing quantum confinement and reducing efficient dielectric screening. Consequently, the exciton binding energies in WS2/hBN/MoS2 heterostructures blueshift comparing to those in WS2/MoS2 heterostructures. In this exciton binding energies tuning process, the reducing dielectric screening effect plays a leading role. In the meantime, the quasi-particle (QP) bandgap remains unchanged before and after 1L-hBN insertion, which is attributed to released quantum confinement and decreased dielectric screening effects canceling each other. Unchanged QP bandgap as along with blueshift exciton binding energies lead to the redshift exciton transition energies in WS2/hBN/MoS2 heterostructures.
The work was financially supported by the National Natural Science Foundation of China (Nos. 11674062, 61775042, and 61774040), the Fudan University–CIOMP Joint Fund (Nos. FC2019-004, FC2019-006, and FC2018-002), the National Key R&D Program of China (No. 2018YFA0703700), the Shanghai Municipal Science and Technology Commission (No. 18JC1410300) and the Shanghai Municipal Natural Science Foundation (No. 20ZR1403200).