![]() ![]() ![]() MoS 2 and WS 2 MLs showed strong PL at ~1.86 and ~1.96 eV 21, respectively, corresponding to their intralayer A excitons of MoS 2 and WS 2 (MoS 2-A and WS 2-A), but both PL signals were considerably quenched by the heterojunction, resulting from the efficient charge transfer. In the type-II HLs, the conduction band minimum (CBM) and the valence band maximum (VBM) are localized to MoS 2 and WS 2 layers, respectively, and efficient charge transfer/separation occurs between the layers, resulting in the formation of the interlayer excitons with long lifetimes 18, 19, 20. The difference in the lattice parameter between MoS 2 and WS 2 MLs is only 0.16% 15, 16, 17, indicating negligible lattice mismatch, and their heterojunction is classified as type II. The mSL effects were also found in strongly lattice-mismatched (~4%) HLs such as WSe 2/WS 2 13 and MoSe 2/WS 2 14, where the moiré period is < 10 nm, but their optical behaviors were explained by the hybridization of the IX and intralayer excitons (X), resulting in the formation of hybridized excitons 14. The broad photoluminescence (PL) of the interlayer excitons (IX) commonly observed in these HLs breaks down into many extremely narrow peaks under extremely low optical pumping at low temperature (<4 K) 10, 12, originating from the excitons trapped in the individual minima of the mSL, called as moiré excitons. The moiré period exceeds 100 nm in MoSe 2/WSe 2 HLs with a small lattice mismatch (<0.2%) 10, 11. Two MLs with a slight lattice mismatch or rotational misalignment brought into contact forming a HL produce a moiré superlattice (mSL) 7, 8, 9 with an additional in-plane periodic potential, and the resulting new length/energy scale provides a powerful means of controlling the quantum phenomena. Two-dimensional (2D) heterobilayers (HLs) assembled from atomically thin monolayers (MLs) of transition-metal dichalcogenides (TMDs) 1, 2 have shown various unique properties of strong interaction with light, fast interlayer charge transfer, and valley-dependent optical selectivity, highly promising for their applications in novel electronic/optoelectronic devices 3, 4, 5, 6. Our findings highlight extendable tuning and remarkable enhancement of light emission from two-dimensional semiconductors by a simple approach of twisted heterojunction in a proper θ range, very useful for their optoelectronic device applications. These novel light-emission behaviors are well explained with reference to theoretical predictions on the avoided crossing between the intralayer and interlayer excitons. The PL intensity shows a similar θ-dependent behavior with its magnitude in the plateau being ∼4 or 80 times larger than that of the WS 2 or MoS 2 ML, respectively. The PL peak energy of the heterobilayer steeply increases (about 120 meV) as θ gets closer to 15 or 52° from 3 or 57°, respectively and reaches a plateau at around 2.01 eV in the θ range from 15 to 52°, higher than that of the separate MoS 2 or WS 2 ML. Here, we first report blue shift of energy and strong enhancement of intensity in the PL by twisted heterojunction of MoS 2 and WS 2 monolayers (MLs) in a particular range of θ. Despite some interesting results on the PL peak shifts by the heterojunction at twist angles ( θ) far from 0 or 60°, all of them are redshifts. Moiré heterostructures produced by twisted heterojunction of transition-metal dichalcogenides are recognized as novel platforms for unique and tunable means of controlling the optical phenomena including photoluminescence (PL). ![]()
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