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Electronic structures of defects and magnetic impurities in MoS2 monolayers.

Lu SC, Leburton JP - Nanoscale Res Lett (2014)

Bottom Line: Specifically, we found VB group impurity elements, such as Ta, substituting Mo to achieve negative formation energy values with impurity states all sitting at less than 0.1 eV from the valence band maximum (VBM), making them the optimal p-type dopant candidates.Among the magnetic impurities such as Mn, Fe, and Co with 1, 2, and 3 magnetic moments/atom, respectively, Mn has the lowest formation energy, the most localized spin distribution, and the nearest impurity level to the conduction band among those elements.Additionally, impurity levels and Fermi level for the above three elements are closer to the conduction band than the previous work (PCCP 16:8990-8996, 2014) which shows the possibility of n-type doping by Mn, thanks to our 5 × 5 cell model.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical and Computer Engineering, and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois, 61801, USA, slu18@illinois.edu.

ABSTRACT
We provide a systematic and theoretical study of the electronic properties of a large number of impurities, vacancies, and adatoms in monolayer MoS2, including groups III and IV dopants, as well as magnetic transition metal atoms such as Mn, Fe, Co, V, Nb, and Ta. By using density functional theory over a 5 × 5 atomic cell, we identify the most promising element candidates for p-doping of MoS2. Specifically, we found VB group impurity elements, such as Ta, substituting Mo to achieve negative formation energy values with impurity states all sitting at less than 0.1 eV from the valence band maximum (VBM), making them the optimal p-type dopant candidates. Moreover, our 5 × 5 cell model shows that B, a group III element, can induce impurity states very close to the VBM with a low formation energy around 0.2 eV, which has not been reported previously. Among the magnetic impurities such as Mn, Fe, and Co with 1, 2, and 3 magnetic moments/atom, respectively, Mn has the lowest formation energy, the most localized spin distribution, and the nearest impurity level to the conduction band among those elements. Additionally, impurity levels and Fermi level for the above three elements are closer to the conduction band than the previous work (PCCP 16:8990-8996, 2014) which shows the possibility of n-type doping by Mn, thanks to our 5 × 5 cell model.

No MeSH data available.


DOS of MoS2doped with (a) C (b) Si (c) Ge (d) B (e) Al, and (f) Ga (solid line). Positive (negative) dotted lines: up-spin (down-spin) states. Pristine MoS2 (Dashed blue line). E = 0 is the VBM. The vertical grey dashed line stands for Fermi level.
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Fig5: DOS of MoS2doped with (a) C (b) Si (c) Ge (d) B (e) Al, and (f) Ga (solid line). Positive (negative) dotted lines: up-spin (down-spin) states. Pristine MoS2 (Dashed blue line). E = 0 is the VBM. The vertical grey dashed line stands for Fermi level.

Mentions: To further assess the possibility of p-type doping by the replacement of S with other group A elements, we choose to study groups III and IV elements, such as C, Si, Ge, B, Al, and Ga that are commonly used in today’s industry. When a C, Si, or Ge atom replaces an S atom, there is a deficit of two valence electrons/atom, but the two remaining electrons have opposite spins, making the system nonmagnetic (Table 1). When substituting C for S, our calculation shows that a mid-gap state appears well above the Fermi level, acting more as a recombination center than as a doping state. For Si dopant, two defect states arise within the bandgap, one at valence band edge and the other close to mid-gap at 0.75 eV from the valence band (Figure 5a). However, the band edge state is already occupied, leaving only the mid-gap state acting as p-dopants or as electron traps, thereby hardly contributing any doping effect as well. In the case of Ge, similar to Si dopants, there are two defect states, with the mid-gap state shifting toward the valence band by approximately 0.3 eV (Figure 5b). Yet at room temperature, it is still quite unlikely to thermally generate a significant amount of free holes through such a state located so far from the VBM.Figure 5


Electronic structures of defects and magnetic impurities in MoS2 monolayers.

Lu SC, Leburton JP - Nanoscale Res Lett (2014)

DOS of MoS2doped with (a) C (b) Si (c) Ge (d) B (e) Al, and (f) Ga (solid line). Positive (negative) dotted lines: up-spin (down-spin) states. Pristine MoS2 (Dashed blue line). E = 0 is the VBM. The vertical grey dashed line stands for Fermi level.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC4494037&req=5

Fig5: DOS of MoS2doped with (a) C (b) Si (c) Ge (d) B (e) Al, and (f) Ga (solid line). Positive (negative) dotted lines: up-spin (down-spin) states. Pristine MoS2 (Dashed blue line). E = 0 is the VBM. The vertical grey dashed line stands for Fermi level.
Mentions: To further assess the possibility of p-type doping by the replacement of S with other group A elements, we choose to study groups III and IV elements, such as C, Si, Ge, B, Al, and Ga that are commonly used in today’s industry. When a C, Si, or Ge atom replaces an S atom, there is a deficit of two valence electrons/atom, but the two remaining electrons have opposite spins, making the system nonmagnetic (Table 1). When substituting C for S, our calculation shows that a mid-gap state appears well above the Fermi level, acting more as a recombination center than as a doping state. For Si dopant, two defect states arise within the bandgap, one at valence band edge and the other close to mid-gap at 0.75 eV from the valence band (Figure 5a). However, the band edge state is already occupied, leaving only the mid-gap state acting as p-dopants or as electron traps, thereby hardly contributing any doping effect as well. In the case of Ge, similar to Si dopants, there are two defect states, with the mid-gap state shifting toward the valence band by approximately 0.3 eV (Figure 5b). Yet at room temperature, it is still quite unlikely to thermally generate a significant amount of free holes through such a state located so far from the VBM.Figure 5

Bottom Line: Specifically, we found VB group impurity elements, such as Ta, substituting Mo to achieve negative formation energy values with impurity states all sitting at less than 0.1 eV from the valence band maximum (VBM), making them the optimal p-type dopant candidates.Among the magnetic impurities such as Mn, Fe, and Co with 1, 2, and 3 magnetic moments/atom, respectively, Mn has the lowest formation energy, the most localized spin distribution, and the nearest impurity level to the conduction band among those elements.Additionally, impurity levels and Fermi level for the above three elements are closer to the conduction band than the previous work (PCCP 16:8990-8996, 2014) which shows the possibility of n-type doping by Mn, thanks to our 5 × 5 cell model.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical and Computer Engineering, and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois, 61801, USA, slu18@illinois.edu.

ABSTRACT
We provide a systematic and theoretical study of the electronic properties of a large number of impurities, vacancies, and adatoms in monolayer MoS2, including groups III and IV dopants, as well as magnetic transition metal atoms such as Mn, Fe, Co, V, Nb, and Ta. By using density functional theory over a 5 × 5 atomic cell, we identify the most promising element candidates for p-doping of MoS2. Specifically, we found VB group impurity elements, such as Ta, substituting Mo to achieve negative formation energy values with impurity states all sitting at less than 0.1 eV from the valence band maximum (VBM), making them the optimal p-type dopant candidates. Moreover, our 5 × 5 cell model shows that B, a group III element, can induce impurity states very close to the VBM with a low formation energy around 0.2 eV, which has not been reported previously. Among the magnetic impurities such as Mn, Fe, and Co with 1, 2, and 3 magnetic moments/atom, respectively, Mn has the lowest formation energy, the most localized spin distribution, and the nearest impurity level to the conduction band among those elements. Additionally, impurity levels and Fermi level for the above three elements are closer to the conduction band than the previous work (PCCP 16:8990-8996, 2014) which shows the possibility of n-type doping by Mn, thanks to our 5 × 5 cell model.

No MeSH data available.