Probing negatively charged and neutral excitons in MoS2/hBN and hBN/MoS2/hBN van der Waals heterostructures

• Published in: Nanotechnology 2021-04, Vol.32 (14), p.145717-145717
• Main Authors: Jadczak, J, Kutrowska-Girzycka, J, Bieniek, M, Kazimierczuk, T, Kossacki, P, Schindler, J J, Debus, J, Watanabe, K, Taniguchi, T, Ho, C H, Wójs, A, Hawrylak, P, Bryja, L
• Format: Article
• Language: English
• Subjects: exciton; factor; molybdenum disulfide; transition metal dichalcogenides monolayers; trion; Zeeman
• ISSN: 0957-4484; 1361-6528
• DOI: 10.1088/1361-6528/abd507

High-quality van der Waals heterostructures assembled from hBN-encapsulated monolayer transition metal dichalcogenides enable observations of subtle optical and spin-valley properties whose identification was beyond the reach of structures exfoliated directly on standard SiO2/Si substrates. Here, we describe different van der Waals heterostructures based on uncapped single-layer MoS2 stacked onto hBN layers of different thicknesses and hBN-encapsulated monolayers. Depending on the doping level, they reveal the fine structure of excitonic complexes, i.e. neutral and charged excitons. In the emission spectra of a particular MoS2/hBN heterostructure without an hBN cap we resolve two trion peaks, T1 and T2, energetically split by about 10 meV, resembling the pair of singlet and triplet trion peaks (TS and TT) in tungsten-based materials. The existence of these trion features suggests that monolayer MoS2 has a dark excitonic ground state, despite having a 'bright' single-particle arrangement of spin-polarized conduction bands. In addition, we show that the effective excitonic g-factor significantly depends on the electron concentration and reaches the lowest value of −2.47 for hBN-encapsulated structures, which reveals a nearly neutral doping regime. In the uncapped MoS2 structures, the excitonic g-factor varies from −1.15 to −1.39 depending on the thickness of the bottom hBN layer and decreases as a function of rising temperature.