Engineering of atomically thin transition metal dichalcogenides (TMDs) is highly sought after for novel optoelectronic and spintronic devices. With the limited number of naturally existing TMDs, chalcogen based alloying has become a viable solution for developing TMDs for optical modulators and photovoltaics. Here, we report on detailed optical and microscopic studies of ternary TMD alloys of molybdenum, sulfur, and selenium grown via a single step method. The developed material has tunable band gaps in a broad range 1.5–1.9 eV with the variation in sulfur compositions. Further, the existence of trions, bi-excitons, and defect bound excitons are shown using temperature dependent (4 K−300 K) photoluminescence spectroscopy. A detailed analysis on MoS1.34Se0.66 alloy system shows the evidence of new types of defect bound excitons originating at low temperatures along with the presence of bi-excitons having a binding energy of ∼41 meV. The prospects of defect induced quasiparticles are observed in scanning transmission electron microscope assisted analyses and verified using density functional theory calculations. The thermal conductivity values, calculated using micro-Raman studies, of MoS2, MoSe2, and MoS1.34Se0.66 are found to be 69(±2) W m−1 K−1, 33(±2) W m−1 K−1 and 17(±2) W m−1 K−1 respectively, in agreement with the theoretical predictions. Tunable optical properties of these ternary atomic layers along with moderate thermal conductivity reveal the potential of these layers in modern opto-electronic devices and sensors.
Bibliographical noteFunding Information:
Authors thank support from the intramural grants at TIFR Hyderabad from the Department of Atomic Energy (DAE). RS thanks Sumit Bawari for helpful discussion about DFT calculations. Ravi K. Biroju and Wolfgang Theis acknowledge the Marie-Sklodowska-Curie individual fellowship under EU H2020 Programme (H2020-MSCA-IF-2017; Grant No: 750929) to carry out some part of this work. AS acknowledges IIT Mandi for low temperature Raman PL facilities.
© 2020 The Author(s). Published by IOP Publishing Ltd
- 2D materials
- Defect bound excitons
- Density functional theory
- Thermal conductivity
ASJC Scopus subject areas
- Materials Science(all)
- Condensed Matter Physics
- Atomic and Molecular Physics, and Optics