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Title: Suppression of Defects and Deep Levels Using Isoelectronic Tungsten Substitution in Monolayer MoSe 2

Abstract

Chemical vapor deposition (CVD) is one of the most promising, scalable synthetic techniques to enable large-area synthesis of two-dimensional (2D) transition metal dichalcogenides (TMDs) for the realization of next generation optoelectronic devices. However, defects formed during the CVD growth process currently limit the quality and electronic properties of 2D TMDs. Effective synthesis and processing strategies to suppress defects and enhance the quality of 2D TMDs are urgently needed. In this work, isoelectrnic doping to produce stable alloy is presented as a new strategy to suppress defects and enhance photoluminescence (PL) in CVD-grown TMD monolayers. The random, isoelectronic substitution of W atoms for Mo atoms in CVD-grown monolayers of Mo 1-xW xSe 2 (02 monolayers. The resultant decrease in defect-medicated non-radiative recombination in the Mo 0.82W 0.18Se 2 monolayers yielded ~10 times more intense PL and extended the carrier lifetime by a factor of 3 compared to pristine CVD-grown MoSe 2 monolayers grown under similar conditions. Low temperatures (4 125 K) PL from defect-related localized states confirms theoretical predictions that isoelectronic W alloying should suppress deep levels in MoSe 2, showing that the defect levels in Mo 1-xW xSe 2 monolayers are higher in energy and quenched more quickly than inmore » MoSe 2. Isoelectronic substitution therefore appears to be a promising synthetic method to control the heterogeneity of 2D TMDs to realize the scalable production of high performance optoelectronic and electronic devices.« less

Authors:
 [1];  [1];  [1];  [1];  [1];  [2];  [1];  [1];  [1];  [2];  [3];  [1];  [1];  [1];  [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Univ. of Kansas, Lawrence, KS (United States)
  3. Univ. of Tennessee, Knoxville, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1360047
Grant/Contract Number:
AC05-00OR22725
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Advanced Functional Materials (Online)
Additional Journal Information:
Journal Name: Advanced Functional Materials (Online); Journal Volume: 27; Journal Issue: 19; Journal ID: ISSN 1616-3028
Publisher:
Wiley
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Li, Xufan, Puretzky, Alexander A., Sang, Xiahan, KC, Santosh, Tian, Mengkun, Ceballos, Frank, Mahjouri-Samani, Masoud, Wang, Kai, Unocic, Raymond R., Zhao, Hui, Duscher, Gerd, Cooper, Valentino R., Rouleau, Christopher M., Geohegan, David B., and Xiao, Kai. Suppression of Defects and Deep Levels Using Isoelectronic Tungsten Substitution in Monolayer MoSe2. United States: N. p., 2017. Web. doi:10.1002/adfm.201603850.
Li, Xufan, Puretzky, Alexander A., Sang, Xiahan, KC, Santosh, Tian, Mengkun, Ceballos, Frank, Mahjouri-Samani, Masoud, Wang, Kai, Unocic, Raymond R., Zhao, Hui, Duscher, Gerd, Cooper, Valentino R., Rouleau, Christopher M., Geohegan, David B., & Xiao, Kai. Suppression of Defects and Deep Levels Using Isoelectronic Tungsten Substitution in Monolayer MoSe2. United States. doi:10.1002/adfm.201603850.
Li, Xufan, Puretzky, Alexander A., Sang, Xiahan, KC, Santosh, Tian, Mengkun, Ceballos, Frank, Mahjouri-Samani, Masoud, Wang, Kai, Unocic, Raymond R., Zhao, Hui, Duscher, Gerd, Cooper, Valentino R., Rouleau, Christopher M., Geohegan, David B., and Xiao, Kai. 2017. "Suppression of Defects and Deep Levels Using Isoelectronic Tungsten Substitution in Monolayer MoSe2". United States. doi:10.1002/adfm.201603850.
@article{osti_1360047,
title = {Suppression of Defects and Deep Levels Using Isoelectronic Tungsten Substitution in Monolayer MoSe2},
author = {Li, Xufan and Puretzky, Alexander A. and Sang, Xiahan and KC, Santosh and Tian, Mengkun and Ceballos, Frank and Mahjouri-Samani, Masoud and Wang, Kai and Unocic, Raymond R. and Zhao, Hui and Duscher, Gerd and Cooper, Valentino R. and Rouleau, Christopher M. and Geohegan, David B. and Xiao, Kai},
abstractNote = {Chemical vapor deposition (CVD) is one of the most promising, scalable synthetic techniques to enable large-area synthesis of two-dimensional (2D) transition metal dichalcogenides (TMDs) for the realization of next generation optoelectronic devices. However, defects formed during the CVD growth process currently limit the quality and electronic properties of 2D TMDs. Effective synthesis and processing strategies to suppress defects and enhance the quality of 2D TMDs are urgently needed. In this work, isoelectrnic doping to produce stable alloy is presented as a new strategy to suppress defects and enhance photoluminescence (PL) in CVD-grown TMD monolayers. The random, isoelectronic substitution of W atoms for Mo atoms in CVD-grown monolayers of Mo1-xWxSe2 (02 monolayers. The resultant decrease in defect-medicated non-radiative recombination in the Mo0.82W0.18Se2 monolayers yielded ~10 times more intense PL and extended the carrier lifetime by a factor of 3 compared to pristine CVD-grown MoSe2 monolayers grown under similar conditions. Low temperatures (4 125 K) PL from defect-related localized states confirms theoretical predictions that isoelectronic W alloying should suppress deep levels in MoSe2, showing that the defect levels in Mo1-xWxSe2 monolayers are higher in energy and quenched more quickly than in MoSe2. Isoelectronic substitution therefore appears to be a promising synthetic method to control the heterogeneity of 2D TMDs to realize the scalable production of high performance optoelectronic and electronic devices.},
doi = {10.1002/adfm.201603850},
journal = {Advanced Functional Materials (Online)},
number = 19,
volume = 27,
place = {United States},
year = 2017,
month = 5
}

Journal Article:
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  • Doping and alloying are effective ways to engineer the band structure and modulate the optoelectronic functionality of monolayer transition metal dichalcogenides (TMDs). In this work, we explore the synthesis and electronic properties of monolayer Mo 1-xW xSe 2 (0 < x < 0.18) alloys with almost 100% alloying degree. The isoelectronic substitutional doping of tungsten for molybdenum in the monolayer MoSe 2 is shown to suppress its intrinsically n-type conduction behavior, with p-type conduction gradually emerging to become dominant with increasing W concentration in the alloys. Atomic resolution Z-contrast electron microscopy show that W is shown to substitute directly formore » Mo without the introduction of noticeable vacancy or interstitial defects, however with randomly-distributed W-rich regions ~2 nm in diameter. Scanning tunneling microscopy/spectroscopy measurements reveal that these W-rich regions exhibit a local band structure with the valence band maximum (VBM) closer to the Fermi level as compared with the Mo-rich regions in the monolayer Mo 1-xW xSe 2 crystal. These localized upshifts of the VBM in the local band structure appear responsible for the overall p-type behavior observed for the monolayer Mo 1-xW xSe 2 crystals. Stacked monolayers of n-type MoSe 2 and p-type Mo 1-xW xSe 2 were demonstrated to form atomically thin, vertically stacked p n homojunctions with gate-tunable characteristics, which appear useful for future optoelectronic applications. Lastly, these results indicate that alloying with isoelectronic dopant atoms appears to be an effective and advantageous alternate strategy to doping or alloying with electron donors or acceptors in two-dimensional TMDs.« less
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  • The synthesis of large-area monolayer tungsten disulphide (WS{sub 2}) single crystal is critical for realistic application in electronic and optical devices. Here, we demonstrate an effective approach to synthesize monolayer WS{sub 2} crystals using tungsten hexachloride (WCl{sub 6}) as a solid precursor in atmospheric chemical vapor deposition process. In this technique, 0.05M solution of WCl{sub 6} in ethanol was drop-casted on SiO{sub 2}/Si substrate to create an even distribution of the precursor, which was reduced and sulfurized at 750 °C in Ar atmosphere. We observed growth of triangular, star-shaped, as well as dendritic WS{sub 2} crystals on the substrate. The crystalmore » geometry evolves with the shape and size of the nuclei as observed from the dendritic structures. These results show that controlling the initial nucleation and growth process, large WS{sub 2} single crystalline monolayer can be grown using the WCl{sub 6} precursor. Our finding shows an easier and effective approach to grow WS{sub 2} monolayer using tungsten halide solution-casting, rather than evaporating the precursor for gas phase reaction.« less
  • Monolayer transition metal dichalcogenides, a new class of atomically thin semiconductors, possess optically coupled 2D valley excitons. The nature of exciton relaxation in these systems is currently poorly understood. Here, we investigate exciton relaxation in monolayer MoSe₂ using polarization-resolved coherent nonlinear optical spectroscopy with high spectral resolution. We report strikingly narrow population pulsation resonances with two different characteristic linewidths of 1 and <0.2 μeV at low temperature. These linewidths are more than 3 orders of magnitude narrower than the photoluminescence and absorption linewidth, and indicate that a component of the exciton relaxation dynamics occurs on time scales longer than 1more » ns. The ultranarrow resonance (<0.2 μeV) emerges with increasing excitation intensity, and implies the existence of a long-lived state whose lifetime exceeds 6 ns.« less