Effects of interlayer coupling on the excitons and electronic structures of WS₂/hBN/MoS₂ van der Waals heterostructures

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.