skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

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. Thu . "Suppression of Defects and Deep Levels Using Isoelectronic Tungsten Substitution in Monolayer MoSe2". United States. doi:10.1002/adfm.201603850. https://www.osti.gov/servlets/purl/1360047.
@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 = {Thu May 18 00:00:00 EDT 2017},
month = {Thu May 18 00:00:00 EDT 2017}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Citation Metrics:
Cited by: 8works
Citation information provided by
Web of Science

Save / Share:
  • 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
  • Defect engineering has been a critical step in controlling the transport characteristics of electronic devices, and the ability to create, tune, and annihilate defects is essential to enable the range of next-generation devices. Whereas defect formation has been well-demonstrated in three-dimensional semiconductors, similar exploration of the heterogeneity in atomically thin two-dimensional semiconductors and the link between their atomic structures, defects, and properties has not yet been extensively studied. In this paper, we demonstrate the growth of MoSe 2–x single crystals with selenium (Se) vacancies far beyond intrinsic levels, up to ~20%, that exhibit a remarkable transition in electrical transport propertiesmore » from n- to p-type character with increasing Se vacancy concentration. A new defect-activated phonon band at ~250 cm -1 appears, and the A 1g Raman characteristic mode at 240 cm -1 softens toward ~230 cm -1 which serves as a fingerprint of vacancy concentration in the crystals. We show that post-selenization using pulsed laser evaporated Se atoms can repair Se-vacant sites to nearly recover the properties of the pristine crystals. Finally, first-principles calculations reveal the underlying mechanisms for the corresponding vacancy-induced electrical and optical transitions.« less
  • Van der Waals bound heterostructures constructed with two-dimensional materials, such as graphene, boron nitride and transition metal dichalcogenides, have sparked wide interest in both device physics and technologies at the two-dimensional limit. One highly coveted heterostructure is that of differing monolayer transition metal dichalcogenides with type-II band alignment, with bound electrons and holes localized in individual monolayers, that is, interlayer excitons. Here, we report the observation of interlayer excitons in monolayer MoSe 2–WSe 2 heterostructures by photoluminescence and photoluminescence excitation spectroscopy. The energy and luminescence intensity are highly tunable by an applied vertical gate voltage. Moreover, we measure an interlayermore » exciton lifetime of ~1.8 ns, an order of magnitude longer than intralayer excitons in monolayers. Ultimately, our work demonstrates optical pumping of interlayer electric polarization, which may provoke further exploration of interlayer exciton condensation, as well as new applications in two-dimensional lasers, light-emitting diodes and photovoltaic devices.« 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. In this paper, we investigate exciton relaxation in monolayer MoSe 2 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 scalesmore » longer than 1 ns. Finally, 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
  • Tailoring the excitonic properties in two-dimensional monolayer transition metal dichalcogenides (TMDs) through strain engineering is an effective means to explore their potential applications in optoelectronics and nanoelectronics. Here we report pressure-tuned photon emission of trions and excitons in monolayer MoSe2 via a diamond anvil cell (DAC) through photoluminescence measurements and theoretical calculations. Under quasi-hydrostatic compressive strain, our results show neutral (X0) and charged (X–) exciton emission of monolayer MoSe2 can be effectively tuned by alcohol mixture vs inert argon pressure transmitting media (PTM). During this process, X– emission undergoes a continuous blue shift until reaching saturation, while X0 emission turnsmore » up splitting. The pressure-dependent charging effect observed in alcohol mixture PTM results in the increase of the X– exciton component and facilitates the pressure-tuned emission of X– excitons. This substantial tunability of X– and X0 excitons in MoSe2 can be extended to other 2D TMDs, which holds potential for developing strained and optical sensing devices.« less