Resonant Energy Transfer in Type-II TMD Heterostructure

In semiconductor heterostructures (HSs) competing interlayer processes such as charge (CT) and energy (ET) transfer compete with each other. Interlayer CT process can be stopped by placing a charge-blocking interlayer between the materials. However, the long-distance interlayer ET process is difficult to stop, unless the materials are placed far apart from each other. Which is not realistic for most of the device applications. Thus, understanding the ET process becomes absolute necessary to design any practical application. Type-II transition metal dichalcogenide (TMD) HSs are believed to be the building block of next generation optoelectronic applications. Earlier studies have found the presence of ET process in type-II HSs after placing a charge-blocking interlayer to completely suppress the CT process. In this work, we show that type-II HS formed between monolayers of Molybdenum Diselenide (MoSe₂) and Rhenium Disulfide (ReS₂), an efficient ET process takes place from ReS₂ to MoSe₂ layer without having any charge-blocking interlayer material, resulting 360% MoSe₂ photoluminescence (PL) enhancement in the HS area. After successfully blocking the CT process by inserting hexagonal Boron Nitride (hBN) layers, more than one order of magnitude higher MoSe₂ PL emission was achieved from the HS area as compared to the MoSe₂ area alone. We calculated the ET efficiency due to the bright exciton to be ~70%. We further prove that this ET process was truly resonant in nature by replacing the MoSe₂ layer with Tungsten Diselenide (WSe₂), where despite forming a similar type-II HS, WSe₂ PL emission was severely quenched in the HS area due to the efficient CT process. This work gives a unique opportunity to simultaneously study the interlayer ET and CT processes in type-II TMD HSs at ultrafast timescale in future works.