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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) Side view of the atomic structure of a non-stoichiometric MoS2/MoOx interface model. The oxygen vacancy site is indicated by an arrow pointing to a circle. Red, purple and yellow spheres represent O, Mo and S atoms, respectively. (b) The corresponding DOS of the defective interface. The green and blue filled lines represent the DOS of S and Mo atoms from the MoS2 layer, whereas red and pink filled lines corresponds to the O and Mo atoms from the MoOx layer. The arrow indicates the gap states caused by an oxygen vacancy in the MoO3 layer.
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f4: (a) Side view of the atomic structure of a non-stoichiometric MoS2/MoOx interface model. The oxygen vacancy site is indicated by an arrow pointing to a circle. Red, purple and yellow spheres represent O, Mo and S atoms, respectively. (b) The corresponding DOS of the defective interface. The green and blue filled lines represent the DOS of S and Mo atoms from the MoS2 layer, whereas red and pink filled lines corresponds to the O and Mo atoms from the MoOx layer. The arrow indicates the gap states caused by an oxygen vacancy in the MoO3 layer.

Mentions: MoO3 is thought to contain a certain amount of oxygen vacancies (up to 3%), and is known to behave as a p-type contact with TMDs or other semiconductors26. Therefore, a model interface structure with oxygen vacancies was also investigated, in order to examine the effect of possible O vacancies on the electronic properties. Indeed, our calculations show that the MoOx interfacial layer can behave as a p-type contact. Moreover, a unique band alignment between (MoS2/MoOx) with an almost zero charge injection barrier is formed, as demonstrated by the DOS shown in Fig. 4(b). The MoS2/MoOx contact does not cause Fermi level pinning, showing a superior contact performance over other true metals171819. Therefore, our results clarify why the defective MoS2/MoOx interface can also be used as an ideal hole contact for TMD-based devices, besides the well-studied organic semiconductors. The presence of O vacancies produce Mo dangling bonds, which induces defect gap states in the upper region of the MoOx band gap (close to the CBM). Moreover, this is an extraordinarily localized effect with only slight changes showed in the electronic structure of the neighboring atoms. These defect states of Mo 4d nature are just empty states that can be easily filled by electron transfer from the valance band of the MoS2 layer, creating the p-type MoS2. In other words, it behaves as a MoOx hole contact layer, injecting holes into the MoS2.


Electronic properties of MoS 2 /MoO x interfaces: Implications in Tunnel Field Effect Transistors and Hole Contacts
(a) Side view of the atomic structure of a non-stoichiometric MoS2/MoOx interface model. The oxygen vacancy site is indicated by an arrow pointing to a circle. Red, purple and yellow spheres represent O, Mo and S atoms, respectively. (b) The corresponding DOS of the defective interface. The green and blue filled lines represent the DOS of S and Mo atoms from the MoS2 layer, whereas red and pink filled lines corresponds to the O and Mo atoms from the MoOx layer. The arrow indicates the gap states caused by an oxygen vacancy in the MoO3 layer.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: (a) Side view of the atomic structure of a non-stoichiometric MoS2/MoOx interface model. The oxygen vacancy site is indicated by an arrow pointing to a circle. Red, purple and yellow spheres represent O, Mo and S atoms, respectively. (b) The corresponding DOS of the defective interface. The green and blue filled lines represent the DOS of S and Mo atoms from the MoS2 layer, whereas red and pink filled lines corresponds to the O and Mo atoms from the MoOx layer. The arrow indicates the gap states caused by an oxygen vacancy in the MoO3 layer.
Mentions: MoO3 is thought to contain a certain amount of oxygen vacancies (up to 3%), and is known to behave as a p-type contact with TMDs or other semiconductors26. Therefore, a model interface structure with oxygen vacancies was also investigated, in order to examine the effect of possible O vacancies on the electronic properties. Indeed, our calculations show that the MoOx interfacial layer can behave as a p-type contact. Moreover, a unique band alignment between (MoS2/MoOx) with an almost zero charge injection barrier is formed, as demonstrated by the DOS shown in Fig. 4(b). The MoS2/MoOx contact does not cause Fermi level pinning, showing a superior contact performance over other true metals171819. Therefore, our results clarify why the defective MoS2/MoOx interface can also be used as an ideal hole contact for TMD-based devices, besides the well-studied organic semiconductors. The presence of O vacancies produce Mo dangling bonds, which induces defect gap states in the upper region of the MoOx band gap (close to the CBM). Moreover, this is an extraordinarily localized effect with only slight changes showed in the electronic structure of the neighboring atoms. These defect states of Mo 4d nature are just empty states that can be easily filled by electron transfer from the valance band of the MoS2 layer, creating the p-type MoS2. In other words, it behaves as a MoOx hole contact layer, injecting holes into the MoS2.

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.