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Electronic properties of MoS 2 /MoO x interfaces: Implications in Tunnel Field Effect Transistors and Hole Contacts

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ABSTRACT

In an electronic device based on two dimensional (2D) transitional metal dichalcogenides (TMDs), finding a low resistance metal contact is critical in order to achieve the desired performance. However, due to the unusual Fermi level pinning in metal/2D TMD interface, the performance is limited. Here, we investigate the electronic properties of TMDs and transition metal oxide (TMO) interfaces (MoS2/MoO3) using density functional theory (DFT). Our results demonstrate that, due to the large work function of MoO3 and the relative band alignment with MoS2, together with small energy gap, the MoS2/MoO3 interface is a good candidate for a tunnel field effect (TFET)-type device. Moreover, if the interface is not stoichiometric because of the presence of oxygen vacancies in MoO3, the heterostructure is more suitable for p-type (hole) contacts, exhibiting an Ohmic electrical behavior as experimentally demonstrated for different TMO/TMD interfaces. Our results reveal that the defect state induced by an oxygen vacancy in the MoO3 aligns with the valance band of MoS2, showing an insignificant impact on the band gap of the TMD. This result highlights the role of oxygen vacancies in oxides on facilitating appropriate contacts at the MoS2 and MoOx (x < 3) interface, which consistently explains the available experimental observations.

No MeSH data available.


(a) Atomic structure of the stoichiometric MoS2/MoO3 interface. Red, purple and yellow spheres represent O, Mo and S atoms, respectively. The interlayer distance was optimized using the DFT + vdW approach. (b) The corresponding DOS of the interface. Green and blue lines represent the DOS of S and Mo atoms from the MoS2 layer, whereas red and pink lines correspond to the O and Mo atoms from the MoO3 layer.
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f3: (a) Atomic structure of the stoichiometric MoS2/MoO3 interface. Red, purple and yellow spheres represent O, Mo and S atoms, respectively. The interlayer distance was optimized using the DFT + vdW approach. (b) The corresponding DOS of the interface. Green and blue lines represent the DOS of S and Mo atoms from the MoS2 layer, whereas red and pink lines correspond to the O and Mo atoms from the MoO3 layer.

Mentions: In order to investigate the electronic properties of the MoS2/MoO3 interface, a heterostructure using the MoO3 (010) and MoS2 (001) monolayer surfaces was constructed and subsequently optimized. If any defects are present, the electronic properties of the pristine MoS2 (001) monolayer will be altered significantly and a surface passivation treatment will be crucial before constructing the interface444546. Figure 3(a) shows the atomic configuration of the MoS2/MoO3 interface model. As stated previously, the corresponding interlayer distance optimization was done using the DFT + vdW approach, to account for the weak MoS2-MoO3 interaction. Our calculations show that standard DFT overestimates the interlayer distance by ∆d ~1.7 Å, with the obtained DFT + vdW result being d(S-O) ~2.8 Å. The DOS of the optimized interface model reveals the relative band alignments between both monolayers. The overall band gap of the pristine MoS2/MoO3 stack is substantially reduced (~0.22 eV) with respect to the respective separate counterparts, due to the metal oxide empty states appearing in the band gap energy range of MoS2. Including the HSE correction, the interface band gap only increases to 0.51 eV, even though the gaps of the individual monolayers widen significantly. As shown in Fig. 3(b), the VBM of MoS2 is located close to the CBM of MoO3.


Electronic properties of MoS 2 /MoO x interfaces: Implications in Tunnel Field Effect Transistors and Hole Contacts
(a) Atomic structure of the stoichiometric MoS2/MoO3 interface. Red, purple and yellow spheres represent O, Mo and S atoms, respectively. The interlayer distance was optimized using the DFT + vdW approach. (b) The corresponding DOS of the interface. Green and blue lines represent the DOS of S and Mo atoms from the MoS2 layer, whereas red and pink lines correspond to the O and Mo atoms from the MoO3 layer.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5035990&req=5

f3: (a) Atomic structure of the stoichiometric MoS2/MoO3 interface. Red, purple and yellow spheres represent O, Mo and S atoms, respectively. The interlayer distance was optimized using the DFT + vdW approach. (b) The corresponding DOS of the interface. Green and blue lines represent the DOS of S and Mo atoms from the MoS2 layer, whereas red and pink lines correspond to the O and Mo atoms from the MoO3 layer.
Mentions: In order to investigate the electronic properties of the MoS2/MoO3 interface, a heterostructure using the MoO3 (010) and MoS2 (001) monolayer surfaces was constructed and subsequently optimized. If any defects are present, the electronic properties of the pristine MoS2 (001) monolayer will be altered significantly and a surface passivation treatment will be crucial before constructing the interface444546. Figure 3(a) shows the atomic configuration of the MoS2/MoO3 interface model. As stated previously, the corresponding interlayer distance optimization was done using the DFT + vdW approach, to account for the weak MoS2-MoO3 interaction. Our calculations show that standard DFT overestimates the interlayer distance by ∆d ~1.7 Å, with the obtained DFT + vdW result being d(S-O) ~2.8 Å. The DOS of the optimized interface model reveals the relative band alignments between both monolayers. The overall band gap of the pristine MoS2/MoO3 stack is substantially reduced (~0.22 eV) with respect to the respective separate counterparts, due to the metal oxide empty states appearing in the band gap energy range of MoS2. Including the HSE correction, the interface band gap only increases to 0.51 eV, even though the gaps of the individual monolayers widen significantly. As shown in Fig. 3(b), the VBM of MoS2 is located close to the CBM of MoO3.

View Article: PubMed Central - PubMed

ABSTRACT

In an electronic device based on two dimensional (2D) transitional metal dichalcogenides (TMDs), finding a low resistance metal contact is critical in order to achieve the desired performance. However, due to the unusual Fermi level pinning in metal/2D TMD interface, the performance is limited. Here, we investigate the electronic properties of TMDs and transition metal oxide (TMO) interfaces (MoS2/MoO3) using density functional theory (DFT). Our results demonstrate that, due to the large work function of MoO3 and the relative band alignment with MoS2, together with small energy gap, the MoS2/MoO3 interface is a good candidate for a tunnel field effect (TFET)-type device. Moreover, if the interface is not stoichiometric because of the presence of oxygen vacancies in MoO3, the heterostructure is more suitable for p-type (hole) contacts, exhibiting an Ohmic electrical behavior as experimentally demonstrated for different TMO/TMD interfaces. Our results reveal that the defect state induced by an oxygen vacancy in the MoO3 aligns with the valance band of MoS2, showing an insignificant impact on the band gap of the TMD. This result highlights the role of oxygen vacancies in oxides on facilitating appropriate contacts at the MoS2 and MoOx (x < 3) interface, which consistently explains the available experimental observations.

No MeSH data available.