Effect of Energy Bands Overlap in the Interlayer Energy Transfer Processes in 2D Heterostructures

Heterostructures (HSs) made by the monolayers (1Ls) of transition metal dichalcogenides (TMDs) have shown great promises in designing next-generation optoelectronic device applications. Interlayer charge (CT) and energy transfer (ET) processes are the main photocarrier relaxation pathways in the TMD HSs. In semiconductor HSs, usually the CT processes happen at a faster timescale (~100s fs) than the nonradiative ET processes (~few ps). CT processes mainly occur due to the energy level offset between the materials and can survive only up to a few nm. Several studies have already been done using different ultrafast spectroscopic techniques to understand the different aspects of the CT process. Whereas, the interlayer ET process mediated by the dipole-dipole coupling between the donor and acceptor materials, can survive up to several tens of nm. Also, due to the experimental challenges to observe the dipole-dipole coupling, many key factors related to the ET processes remain incomprehensible. In this talk, I would like to present our recent studies to understand the effect of energy bands overlap in the ET process in TMD HSs. First, we study the effect of resonant overlaps between the optical bandgaps of two materials [1]. In this work, we showed that in the type-II HSs formed using the 1Ls of molybdenum diselenide (MoSe₂) and rhenium disulfide (ReS₂), an ET process dominates over the fast CT process, resulting 360% photoluminescence (PL) enhancement in the HS area. After completely blocking the CT process, this enhancement increased further up to more than 1 order of magnitude higher. In the second part, we showed that HS formed between the 1Ls of molybdenum disulfide (MoS₂) and tungsten disulfide (WSe₂), an unusual ET process occur from the lower bandgap WSe₂ to higher bandgap MoS₂ due to the resonant overlaps between the high-lying excitonic states [2]. These works will help us to realize the complex ET processes in TMD HSs for better development of the TMD-based novel optoelectronic device applications.<br/><br/>References:<br/>[1] A. Karmakar, A. Al-Mahboob, C. E. Petoukhoff, O. Kravchyna, N. S. Chan, T. Taniguchi, K. Watanabe, K. M. Dani<i>, </i>''Dominating Interlayer Resonant Energy Transfer in Type-II 2D Heterostructure'', <i>ACS Nano 2022, 16, 3, 3861–3869</i>.<br/>[2] A. Karmakar, T. Kazimierczuk, I. Antoniazzi, M. Raczynski, S. Park, H. Jang, T. Taniguchi, K. Watanabe, A. Babinski, A. Al-Mahboob, M. R. Molas<i>, </i>'' Excitation-Dependent High-Lying Excitonic Exchange <i>via</i> Interlayer Energy Transfer from <i>Lower-to-Higher</i> Bandgap 2D Material'', <i>Nano Lett. 2023, 23, 12, 5617–5624</i>.