| Autor: |
Hsu WT; Department of Electrophysics, National Chiao Tung University, Hsinchu, 30010, Taiwan., Lu LS; Department of Electrophysics, National Chiao Tung University, Hsinchu, 30010, Taiwan., Wang D; Department of Electrophysics, National Chiao Tung University, Hsinchu, 30010, Taiwan., Huang JK; Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia., Li MY; Research Center for Applied Sciences, Academia Sinica, Taipei, 10617, Taiwan., Chang TR; Department of Physics, National Cheng Kung University, Tainan, 70101, Taiwan., Chou YC; Department of Electrophysics, National Chiao Tung University, Hsinchu, 30010, Taiwan., Juang ZY; Department of Electrophysics, National Chiao Tung University, Hsinchu, 30010, Taiwan., Jeng HT; Department of Physics, National Tsing Hua University, Hsinchu, 30013, Taiwan., Li LJ; Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia., Chang WH; Department of Electrophysics, National Chiao Tung University, Hsinchu, 30010, Taiwan. whchang@mail.nctu.edu.tw. |
| Abstrakt: |
Monolayer transition metal dichalcogenides, such as MoS 2 and WSe 2 , have been known as direct gap semiconductors and emerged as new optically active materials for novel device applications. Here we reexamine their direct gap properties by investigating the strain effects on the photoluminescence of monolayer MoS 2 and WSe 2 . Instead of applying stress, we investigate the strain effects by imaging the direct exciton populations in monolayer WSe 2 -MoS 2 and MoSe 2 -WSe 2 lateral heterojunctions with inherent strain inhomogeneity. We find that unstrained monolayer WSe 2 is actually an indirect gap material, as manifested in the observed photoluminescence intensity-energy correlation, from which the difference between the direct and indirect optical gaps can be extracted by analyzing the exciton thermal populations. Our findings combined with the estimated exciton binding energy further indicate that monolayer WSe 2 exhibits an indirect quasiparticle gap, which has to be reconsidered in further studies for its fundamental properties and device applications.Monolayer transition metal dichalcogenides have so far been thought to be direct bandgap semiconductors. Here, the authors revisit this assumption and find that unstrained monolayer WSe 2 is an indirect-gap material, as evidenced by the observed photoluminescence intensity-energy correlation. |
