Indirect to direct band gap crossover in two-dimensional WS2(1−x)Se2x alloys
Source abstract
Abstract
Abstract In atomically thin transition metal dichalcogenide semiconductors, there is a crossover from indirect to direct band gap as the thickness drops to one monolayer, which comes with a fast increase of the photoluminescence signal. Here, we show that for different alloy compositions of WS2(1−x)Se2x this trend may be significantly affected by the alloy content and we demonstrate that the sample with the highest Se ratio presents a strongly reduced effect. The highest micro-PL intensity is found for bilayer WS2(1−x)Se2x (x = 0.8) with a decrease of its maximum value by only a factor of 2 when passing from mono-layer to bi-layer. To better understand this factor and explore the layer-dependent band structure evolution of WS2(1−x)Se2x, we performed a nano-angle-resolved photoemission spectroscopy study coupled with first-principles calculations. We find that the high micro-PL value for bilayer WS2(1−x)Se2x (x = 0.8) is due to the overlay of direct and indirect optical transitions. This peculiar high PL intensity in WS2(1−x)Se2x opens the way for spectrally tunable light-emitting devices.
Source: crossref · Quality: baseline
Research context
OpenAlex topics: 2D Materials and Applications · Graphene research and applications · Chalcogenide Semiconductor Thin Films
SciVX discovery tags are terminology-based. OpenAlex topics are source-provided classifications.
References (50)
Show source-provided references
1. Geim, A. K. & Grigorieva, I. V. Van der Waals heterostructures. Nature 499, 419–425 (2013).10.1038/nature12385 ↗
2. Radisavljevic, B., Radenovic, A., Brivio, J., Giacometti, V. & Kis, A. Single-layer MoS2 transistors. Nat. Nanotechnol. 6, 147–150 (2011).10.1038/nnano.2010.279 ↗
3. Xiao, D., Liu, G.-B., Feng, W., Xu, X. & Yao, W. Coupled spin and valley physics in monolayers of MoS2 and other group-VI dichalcogenides. Phys. Rev. Lett. 108, 196802 (2012).10.1103/PhysRevLett.108.196802 ↗
4. Mak, K. F., He, K., Shan, J. & Heinz, T. F. Control of valley polarization in monolayer MoS2 by optical helicity. Nat. Nanotechnol. 7, 494–498 (2012).10.1038/nnano.2012.96 ↗
5. Zeng, H., Dai, J., Yao, W., Xiao, D. & Cui, X. Valley polarization in MoS2 monolayers by optical pumping. Nat. Nanotechnol. 7, 490–493 (2012).10.1038/nnano.2012.95 ↗
6. Cao, Y. et al. Unconventional superconductivity in magic-angle graphene superlattices. Nature 556, 43–50 (2018).10.1038/nature26160 ↗
7. Li, F., Wei, W., Zhao, P., Huang, B. & Dai, Y. Electronic and optical properties of pristine and vertical and lateral heterostructures of Janus MoSSe and WSSe. J. Chem. Lett. 8, 5959–5965 (2017).10.1021/acs.jpclett.7b02841 ↗
8. Zheng, B. et al. Band alignment engineering in two-dimensional lateral heterostructures. J. Am. Chem. Soc. 140, 11193–11197 (2018).10.1021/jacs.8b07401 ↗
9. Li, H. et al. Lateral growth of composition graded atomic layer MoS2(1-x)Se2x nanosheets. J. Am. Chem. Soc. 137, 5284–5287 (2015).10.1021/jacs.5b01594 ↗
10. Li, H. et al. Growth of alloy MoS2xSe2x(1-x) nanosheets with fully tunable chemical compositions and optical properties. J. Am. Chem. Soc. 136, 3756–3759 (2014).10.1021/ja500069b ↗
11. Lagarde, D. et al. Carrier and polarization dynamics in monolayer MoS2. Phys. Rev. Lett. 112, 047401 (2014).10.1103/PhysRevLett.112.047401 ↗
12. Magnozzi, M. et al. Optical dielectric function of two-dimensional WS2 on epitaxial graphene. 2D Mater. 7, 2 (2020).10.1088/2053-1583/ab6f0b ↗
13. Noumbé, U. N. et al. Ionic glass-gated 2D material-based phototransistor: MoSe2 over LaF3 as case study. Adv. Funct. Mater. 29, 1902723 (2019).10.1002/adfm.201902723 ↗
14. Britnell, L. et al. Strong light–matter interactions in heterostructures of atomically. Thin Films. 340, 1311–1314 (2013).
15. Zhou, X. et al. Tunneling diode based on WSe2/SnS2 heterostructure incorporating high detectivity and responsivity. Adv. Mater. 30, 1703286 (2018).10.1002/adma.201703286 ↗
16. Wang, G. et al. Spin-orbit engineering in transition metal dichalcogenide alloy monolayers. Nat. Commun. 6, 10110 (2015).10.1038/ncomms10110 ↗
17. Yun, W. S., Han, S. W., Hong, S. C., Kim, I. G. & Lee, J. D. Thickness and strain effects on electronic structures of transition metal dichalcogenides: 2H-MX2 semiconductors (M = Mo, W; X = S, Se, Te). Phys. Rev. B 85, 033305 (2012).10.1103/PhysRevB.85.033305 ↗
18. Jin, W. et al. Direct measurement of the thickness-dependent electronic band structure of MoS2 using angle-resolved photoemission spectroscopy. Phys. Rev. Lett. 111, 106801 (2013).10.1103/PhysRevLett.111.106801 ↗
19. Ben Aziza, Z. et al. Bandgap inhomogeneity of MoS2 monolayer on epitaxial graphene bilayer in van der Waals p-n junction. Carbon 110, 396–403 (2016).10.1016/j.carbon.2016.09.041 ↗
20. Chaste, J. et al. Intrinsic properties of suspended MoS2 on SiO2/Si pillar arrays for nanomechanics and optics. ACS Nano 12, 3235–3242 (2018).10.1021/acsnano.7b07689 ↗
21. Blundo, E. et al. Evidence of the direct-to-indirect band gap transition in strained two-dimensional WS2, MoS2, and WSe2. Phys. Rev. Res. 2, 012024(R) (2020).10.1103/PhysRevResearch.2.012024 ↗
22. Pető, J. et al. Moderate strain induced indirect bandgap and conduction electrons in MoS2 single layers. npj 2D Mater. Appl. 3, 39 (2019).10.1038/s41699-019-0123-5 ↗
23. Waldecker, L. et al. Rigid band shifts in two-dimensional semiconductors through external dielectric screening. Phys. Rev. Lett. 123, 206403 (2019).10.1103/PhysRevLett.123.206403 ↗
24. Mak, K. F., Lee, C., Hone, J., Shan, J. & Heinz, T. F. Atomically thin MoS2: a new direct-gap semiconductor. Phys. Rev. Lett. 105, 136805 (2010).10.1103/PhysRevLett.105.136805 ↗
25. Lezama, I. G. et al. Indirect-to-direct band gap crossover in few-layer MoTe2. Nano Lett. 15, 2336–2342 (2015).10.1021/nl5045007 ↗
26. Conley, H. J. et al. Bandgap engineering of strained monolayer and bilayer MoS2. Nano Lett. 13, 3626–3630 (2013).10.1021/nl4014748 ↗
27. Yang, T. et al. van der Waals epitaxial growth and optoelectronics of large-scale WSe2/SnS2 vertical bilayer p–n junctions. Nat. Commun. 8, 1906 (2017).10.1038/s41467-017-02093-z ↗
28. Duan, X. et al. Synthesis of WS2xSe2-2x alloy nanosheets with composition-tunable electronic properties. Nano Lett. 16, 264–269 (2016).10.1021/acs.nanolett.5b03662 ↗
29. Zribi, J. et al. Strong interlayer hybridization in the aligned SnS2/WSe2 hetero-bilayer structure. npj 2D Mater. Appl. 3, 27 (2019).10.1038/s41699-019-0109-3 ↗
30. Henck, H. et al. Electronic band structure of two-dimensional WS2/graphene van der Waals heterostructures. Phys. Rev. B 97, 155421 (2018).10.1103/PhysRevB.97.155421 ↗
31. Chen, Y. et al. Tunable band-gap photoluminescence from atomically thin transition-metal dichalcogenide alloys. ACS Nano 7, 4610–4616 (2013).10.1021/nn401420h ↗
32. Paradisanos, I. et al. Controlling interlayer excitons in MoS2 layers grown by chemical vapor deposition. Nat. Commun. 11, 2391 (2020).10.1038/s41467-020-16023-z ↗
33. Pierucci, D. et al. Band alignment and minigaps in monolayer MoS2–Graphene van der Waals heterostructures. Nano Lett. 16, 4054–4061 (2016).10.1021/acs.nanolett.6b00609 ↗
34. Henck, H. et al. Flat electronic bands in long sequences of rhombohedral-stacked graphene. Phys. Rev. B 97, 245421 (2018).10.1103/PhysRevB.97.245421 ↗
35. Henck, H. et al. Direct observation of the band structure in bulk hexagonal boron nitride. Phys. Rev. B 95, 085410 (2017).10.1103/PhysRevB.95.085410 ↗
36. Ben Aziza, Z. et al. Van der Waals epitaxy of GaSe/Graphene heterostructure: electronic and interfacial properties. ACS Nano 10, 9679–9686 (2016).10.1021/acsnano.6b05521 ↗
37. Forti, S. et al. Electronic properties of single-layer tungsten disulfide on epitaxial graphene on silicon carbide. Nanoscale 9, 16412–16419 (2017).10.1039/C7NR05495E ↗
38. Nakamura, H. et al. Spin splitting and strain in epitaxial monolayer WSe2 on graphene. Phys. Rev. B 101, 165103 (2020).10.1103/PhysRevB.101.165103 ↗
39. Pierucci, D. et al. Tunable doping in hydrogenated single layered molybdenum disulfide. ACS Nano 11, 1755–1761 (2017).10.1021/acsnano.6b07661 ↗
40. Dau, M. T. et al. Beyond van der Waals interaction: the case of MoSe2 epitaxially grown on few-layer graphene. ACS Nano 12, 2319–2331 (2018).10.1021/acsnano.7b07446 ↗
41. Henck, H. et al. Interface dipole and band bending in the hybrid p–n heterojunction MoS2/GaN(0001). Phys. Rev. B 96, 115312 (2017).10.1103/PhysRevB.96.115312 ↗
42. Zhang, Y. et al. Direct observation of the transition from indirect to direct bandgap in atomically thin epitaxial MoSe2. Nat. Nanotechnol. 9, 111–115 (2014).10.1038/nnano.2013.277 ↗
43. Ulstrup, S. et al. Nanoscale mapping of quasiparticle band alignment. Nat. Commun. 10, 3283 (2019).10.1038/s41467-019-11253-2 ↗
44. Pierucci, D. et al. Large area molybdenum disulphide-epitaxial graphene vertical Van der Waals heterostructures. Sci. Rep. 6, 26656 (2016).10.1038/srep26656 ↗
45. Wilson, N. R. et al. Determination of band offsets, hybridization, and exciton binding in 2D semiconductor heterostructures. Sci. Adv. 3, e1601832 (2017).10.1126/sciadv.1601832 ↗
46. Zhang, Y. et al. Electronic structure, surface doping, and optical response in epitaxial WSe2 thin films. Nano Lett. 16, 2485–2491 (2016).10.1021/acs.nanolett.6b00059 ↗
47. Steinhoff, A. et al. Efficient excitonic photoluminescence in direct and indirect band gap monolayer MoS2. Nano Lett. 15, 6841–6847 (2015).10.1021/acs.nanolett.5b02719 ↗
48. Giannozzi, P. et al. QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials. J. Phys. Condens. Matter 21, 39 (2009).10.1088/0953-8984/21/39/395502 ↗
49. Heyd, J., Scuseria, G. E. & Ernzerhof, M. Hybrid functionals based on a screened Coulomb potential. J. Chem. Phys. 118, 8207 (2003).10.1063/1.1564060 ↗
50. Grimme, S., Antony, J., Ehrlich, S. & Krieg, H. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 132, 154104 (2010).10.1063/1.3382344 ↗