Anomalously polarised emission from a MoS₂/WS₂heterostructure

Abstract

We report circularly polarised emission, with helicity opposite to the optical excitation, from a van der Waals heterostructure (HS) consisting of a monolayer MoS2 and three-layer WS2. Selective excitation of...

Negative Valley Polarization of the Intralayer Exciton via One-Step Growth of H-Type Heterobilayer WS2/MoS2

“…Clearly, our model underscores the role of the stacking order in the heterobilayer because it significantly affects relaxation channels of the valley-polarized charges, which in turn impacts the sign of the resultant DoCP. This further rules out the simple attribution to an n-doping-induced valley flip at X Mo during the growth of the VH as interpreted by Mol et al…”

“…Clearly, the opposite valley response occurs when WS 2 is first excited in the H-type VH but cannot occur when MoS 2 is directly excited, which is also consistent with the previous literature. 10 These contrasting responses of the H-type VH at the two distinctive excitation energies imply that interlayer charge transfer from WS 2 to MoS 2 is necessary for the valley-flip process at the ±K valleys.…”

“…For instance, the sign for the DoCP of interlayer excitons can be switched by controlling the stacking orders, as has been well demonstrated in R-/H-type heterobilayer WSe 2 /MoSe 2 , where subsequent ultrafast charge transfer occurs from one layer to another as a result of type II band alignment. 8,9 Intriguingly, the negative DoCP of intralayer excitons at the ±K valleys has been recently reported in the system of MoS 2 /trilayer-WS 2 by Mol et al 10 However, the origin for the observed cross-helicity in the PL was not properly understood.…”

“…In this article, we investigate valley polarization responses of intralayer excitons in heterobilayers of WS 2 /MoS 2 exhibiting the striking effect of negative helicity emission and provide the interpretation of this intriguing phenomenon on the basis of stacking order and excitation energy as well. Unlike previous works, 10 we employed commensurate WS 2 /MoS 2 vertical heterobilayers (VHs) prepared with the two well-defined Hand R-type stacking orders by one-step chemical vapor deposition (CVD). The distinct stacking-order dependence of valley-contrasting responses was demonstrated at room temperature and more profoundly at low temperatures by systematically investigating the excitation energy and temperature dependences of polarization-resolved PL from the two distinct structural phases of WS 2 /MoS 2 VHs.…”

Twist-Dependent Tuning of Excitonic Emissions in Bilayer WSe2

“…Synthesis of monolayer (ML)-to-few-layer TMDCs using chemical vapor deposition (CVD) has already been reported by many research groups, − and their layer-dependent electronic, optical, and vibrational properties have also been investigated in sufficient detail. − In the last few years, there has been a surge of interest in the heterojunction of these ML TMDCs. − Owing to a large number of TMDCs being available, a variety of combinations have been implemented in the literature to observe several unique intriguing optical and electrical features. − This leads to a strong motivation to understand how the twist affects interlayer interactions and the excitonic level properties in these materials. However, limited investigations are available on homobilayer systems, which are essential for emerging applications in twistronics, spintronics, valleytronics, and optoelectronics.…”