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Thickness Considerations of Two-Dimensional Layered Semiconductors for Transistor Applications.

Zhang Y, Li H, Wang H, Xie H, Liu R, Zhang SL, Qiu ZJ - Sci Rep (2016)

Bottom Line: The decrease in Ion/Ioff is exponential for t between 20 nm and 100 nm, by a factor of 10 for each additional 10 nm.This excellent agreement confirms that multilayer-MoS2 films can be approximated as a homogeneous semiconductor with high surface conductivity that tends to deteriorate Ion/Ioff.Our findings are helpful in guiding material synthesis and designing advanced field-effect transistors based on the layered semiconductors.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of ASIC and System, School of Information Science and Technology, Fudan University, Shanghai 200433, China.

ABSTRACT
Layered two-dimensional semiconductors have attracted tremendous attention owing to their demonstrated excellent transistor switching characteristics with a large ratio of on-state to off-state current, Ion/Ioff. However, the depletion-mode nature of the transistors sets a limit on the thickness of the layered semiconductor films primarily determined by a given Ion/Ioff as an acceptable specification. Identifying the optimum thickness range is of significance for material synthesis and device fabrication. Here, we systematically investigate the thickness-dependent switching behavior of transistors with a wide thickness range of multilayer-MoS2 films. A difference in Ion/Ioff by several orders of magnitude is observed when the film thickness, t, approaches a critical depletion width. The decrease in Ion/Ioff is exponential for t between 20 nm and 100 nm, by a factor of 10 for each additional 10 nm. For t larger than 100 nm, Ion/Ioff approaches unity. Simulation using technical computer-aided tools established for silicon technology faithfully reproduces the experimentally determined scaling behavior of Ion/Ioff with t. This excellent agreement confirms that multilayer-MoS2 films can be approximated as a homogeneous semiconductor with high surface conductivity that tends to deteriorate Ion/Ioff. Our findings are helpful in guiding material synthesis and designing advanced field-effect transistors based on the layered semiconductors.

No MeSH data available.


Carrier distribution in 50-nm (a) and 100-nm (b) MoS2 at various Vg. (c,d) Electron and hole current distributions in a 100-nm-thick MoS2 at Vg = −30 V.
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f5: Carrier distribution in 50-nm (a) and 100-nm (b) MoS2 at various Vg. (c,d) Electron and hole current distributions in a 100-nm-thick MoS2 at Vg = −30 V.

Mentions: As the device switching behavior is mainly determined by Ioff, the carrier distribution at negative Vg is shown, respectively, in Fig. 5a,b for t < Wmax and t > Wmax. At a negative Vg, electrons are repelled from while holes are attracted to the MoS2/SiO2 interface. For t < Wmax, electrons are depleted in the whole MoS2 film at Vg < −25 V. Simultaneously, an inversion layer populated with holes is formed at the MoS2/SiO2 interface. However, when t > Wmax, the carrier concentration close to the sample surface (away from the MoS2/SiO2 interface) remains constant independent of Vg. This is a result of charge screening effect that results in a poor electrostatic control of the electrons in the excess part of the MoS2 film. This high and uncontrolled electron concentration in this excess MoS2 close to the sample surface, shown in Fig. 5c, contributes to Ioff. Although a hole inversion layer is formed under large negative Vg, the hole conduction current can be neglected due to a large SBH at the contact interfaces (see Fig. 5d).


Thickness Considerations of Two-Dimensional Layered Semiconductors for Transistor Applications.

Zhang Y, Li H, Wang H, Xie H, Liu R, Zhang SL, Qiu ZJ - Sci Rep (2016)

Carrier distribution in 50-nm (a) and 100-nm (b) MoS2 at various Vg. (c,d) Electron and hole current distributions in a 100-nm-thick MoS2 at Vg = −30 V.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4940740&req=5

f5: Carrier distribution in 50-nm (a) and 100-nm (b) MoS2 at various Vg. (c,d) Electron and hole current distributions in a 100-nm-thick MoS2 at Vg = −30 V.
Mentions: As the device switching behavior is mainly determined by Ioff, the carrier distribution at negative Vg is shown, respectively, in Fig. 5a,b for t < Wmax and t > Wmax. At a negative Vg, electrons are repelled from while holes are attracted to the MoS2/SiO2 interface. For t < Wmax, electrons are depleted in the whole MoS2 film at Vg < −25 V. Simultaneously, an inversion layer populated with holes is formed at the MoS2/SiO2 interface. However, when t > Wmax, the carrier concentration close to the sample surface (away from the MoS2/SiO2 interface) remains constant independent of Vg. This is a result of charge screening effect that results in a poor electrostatic control of the electrons in the excess part of the MoS2 film. This high and uncontrolled electron concentration in this excess MoS2 close to the sample surface, shown in Fig. 5c, contributes to Ioff. Although a hole inversion layer is formed under large negative Vg, the hole conduction current can be neglected due to a large SBH at the contact interfaces (see Fig. 5d).

Bottom Line: The decrease in Ion/Ioff is exponential for t between 20 nm and 100 nm, by a factor of 10 for each additional 10 nm.This excellent agreement confirms that multilayer-MoS2 films can be approximated as a homogeneous semiconductor with high surface conductivity that tends to deteriorate Ion/Ioff.Our findings are helpful in guiding material synthesis and designing advanced field-effect transistors based on the layered semiconductors.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of ASIC and System, School of Information Science and Technology, Fudan University, Shanghai 200433, China.

ABSTRACT
Layered two-dimensional semiconductors have attracted tremendous attention owing to their demonstrated excellent transistor switching characteristics with a large ratio of on-state to off-state current, Ion/Ioff. However, the depletion-mode nature of the transistors sets a limit on the thickness of the layered semiconductor films primarily determined by a given Ion/Ioff as an acceptable specification. Identifying the optimum thickness range is of significance for material synthesis and device fabrication. Here, we systematically investigate the thickness-dependent switching behavior of transistors with a wide thickness range of multilayer-MoS2 films. A difference in Ion/Ioff by several orders of magnitude is observed when the film thickness, t, approaches a critical depletion width. The decrease in Ion/Ioff is exponential for t between 20 nm and 100 nm, by a factor of 10 for each additional 10 nm. For t larger than 100 nm, Ion/Ioff approaches unity. Simulation using technical computer-aided tools established for silicon technology faithfully reproduces the experimentally determined scaling behavior of Ion/Ioff with t. This excellent agreement confirms that multilayer-MoS2 films can be approximated as a homogeneous semiconductor with high surface conductivity that tends to deteriorate Ion/Ioff. Our findings are helpful in guiding material synthesis and designing advanced field-effect transistors based on the layered semiconductors.

No MeSH data available.