Journal
NANO LETTERS
Volume 15, Issue 12, Pages 8223-8228Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.5b03740
Keywords
Electroluminescence; photoluminescence; transition metal dichalcogenides; tungsten diselenide; hexagonal boron nitride; graphene; van der Waals heterostructure
Categories
Funding
- European Research Council Synergy Grant Hetero2D
- EC-FET European Graphene Flagship
- Royal Society
- Royal Academy of Engineering
- U.S. Army
- European Science Foundation (ESF) under the EUROCORES Programme EuroGRAPHENE (GOSPEL)
- Engineering and Physical Sciences Research Council (U.K.)
- Leverhulme Trust (U.K.)
- U.S. Office of Naval Research
- U.S. Defence Threat Reduction Agency
- U.S. Air Force Office of Scientific Research
- FP7 ITN S3NANO
- SEP-Mexico
- CONACYT
- EPSRC [EP/K005014/1] Funding Source: UKRI
- Engineering and Physical Sciences Research Council [EP/K005014/1] Funding Source: researchfish
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Monolayers of molybdenum and tungsten dichalcogenides are direct bandgap semiconductors, which makes them promising for optoelectronic applications. In particular, van der Waals heterostructures consisting of monolayers of MoS2 sandwiched between atomically thin hexagonal boron nitride (hBN) and graphene electrodes allows one to obtain light emitting quantum wells (LEQWs) with low-temperature external quantum efficiency (EQE) of 1%. However, the EQE of MoS2- and MoSe2- based LEQWs shows behavior common for many other materials: it decreases fast from cryogenic conditions to room temperature, undermining their practical applications. Here we compare MoSe2- and WSe2 LEQWs. We show that the EQE of WSe, devices grows with temperature, with room temperature EQE reaching 5%, which is 250X more than the previous best performance of MoS, and MoSe2 quantum wells in ambient conditions. We attribute such different temperature dependences to the inverted sign of spin-orbit splitting of conduction band states in tungsten and molybdenum dichalcogenides, which makes the lowest-energy exciton in WSe2 dark.
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