Limits...
Novel field-effect Schottky barrier transistors based on graphene-MoS2 heterojunctions.

Tian H, Tan Z, Wu C, Wang X, Mohammad MA, Xie D, Yang Y, Wang J, Li LJ, Xu J, Ren TL - Sci Rep (2014)

Bottom Line: Recently, two-dimensional materials such as molybdenum disulphide (MoS2) have been demonstrated to realize field effect transistors (FET) with a large current on-off ratio.Moreover, the field effective mobility of the FESBT is up to 58.7 cm(2)/V · s.Our theoretical analysis shows that if the thickness of oxide is further reduced, a subthreshold swing (SS) of 40 mV/decade can be maintained within three orders of drain current at room temperature.

View Article: PubMed Central - PubMed

Affiliation: 1] Institute of Microelectronics, Tsinghua University, Beijing 100084, China [2] Tsinghua National Laboratory for Information Science and Technology (TNList), Tsinghua University, Beijing 100084, China [3].

ABSTRACT
Recently, two-dimensional materials such as molybdenum disulphide (MoS2) have been demonstrated to realize field effect transistors (FET) with a large current on-off ratio. However, the carrier mobility in backgate MoS2 FET is rather low (typically 0.5-20 cm(2)/V · s). Here, we report a novel field-effect Schottky barrier transistors (FESBT) based on graphene-MoS2 heterojunction (GMH), where the characteristics of high mobility from graphene and high on-off ratio from MoS2 are properly balanced in the novel transistors. Large modulation on the device current (on/off ratio of 10(5)) is achieved by adjusting the backgate (through 300 nm SiO2) voltage to modulate the graphene-MoS2 Schottky barrier. Moreover, the field effective mobility of the FESBT is up to 58.7 cm(2)/V · s. Our theoretical analysis shows that if the thickness of oxide is further reduced, a subthreshold swing (SS) of 40 mV/decade can be maintained within three orders of drain current at room temperature. This provides an opportunity to overcome the limitation of 60 mV/decade for conventional CMOS devices. The FESBT implemented with a high on-off ratio, a relatively high mobility and a low subthreshold promises low-voltage and low-power applications for future electronics.

No MeSH data available.


Related in: MedlinePlus

The theoretical model of the gate controlled GMH.(a) The schematic structure of the gate controlled GMH. The MoS2 is sandwiched between the graphene and the SiO2. (b) The Schottky barrier height obtained from different gate bias by solving the Poisson equation. Large (0.34 eV) Fermi level shift is obtained by −40 to 40 V gate control. (c) The simulations (Lines) and experiments (Points) of the FESBT. (d) Theoretical analysis showing that the subthreshold swing of FESBT overcomes the limitation of 60 mV/dec of conventional FET. (e) The mobility vs. the Vgate showing a maximum mobility of 58.7 cm2/V·s. The mobility is induced from the experimental results in Fig. 2c at 0.1 V bias. (f) The mobility vs. the Schottky barrier height showing that the maximum mobility is obtained at a barrier height of 0.26 eV.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4127518&req=5

f4: The theoretical model of the gate controlled GMH.(a) The schematic structure of the gate controlled GMH. The MoS2 is sandwiched between the graphene and the SiO2. (b) The Schottky barrier height obtained from different gate bias by solving the Poisson equation. Large (0.34 eV) Fermi level shift is obtained by −40 to 40 V gate control. (c) The simulations (Lines) and experiments (Points) of the FESBT. (d) Theoretical analysis showing that the subthreshold swing of FESBT overcomes the limitation of 60 mV/dec of conventional FET. (e) The mobility vs. the Vgate showing a maximum mobility of 58.7 cm2/V·s. The mobility is induced from the experimental results in Fig. 2c at 0.1 V bias. (f) The mobility vs. the Schottky barrier height showing that the maximum mobility is obtained at a barrier height of 0.26 eV.

Mentions: The graphene-MoS2 heterojunction is the core of FESBT devices. In order to fundamentally understand the physics of the heterojunction, a theoretical model is established. As illustrated in Figure 4a, the model consists of three parts: a Schottky junction formed by the GMH and two resistors connected with the source and drain terminals. The electrical performance of our device is mainly dependent on the heterojunction. In this case, the lateral transport is the dominant factor, suggesting that the resistance of this uniform junction is scaled with Ljunction/Wjunction. Therefore, the junction could also be regarded as an artificial thin film FET. These two resistors are included to consider the resistances of graphene and MoS2 between the junction and source/drain electrodes. Here MoS2 is considered as a thin bulk material, and the drop of electric potential in graphene is ignored since it has only several layers. The integral of electric field along the path perpendicular to the plane equals to the difference of work function between MoS2 and gate, assuming that the electric field is constant in graphene and MoS2, respectively. where , , , and Vch are the electric field, the thicknesses of the oxide and MoS2, the difference of the work functions between MoS2 and gate electrode, and the channel potential of graphene. The electric field is consistent at the interface between the oxide and the MoS2, where is the relative dielectric constant of the oxide and the MoS2. As the electric field penetrates into graphene, it induces free charges, so we obtain where e and n2D are electron charge and two-dimensional carrier density in graphene.


Novel field-effect Schottky barrier transistors based on graphene-MoS2 heterojunctions.

Tian H, Tan Z, Wu C, Wang X, Mohammad MA, Xie D, Yang Y, Wang J, Li LJ, Xu J, Ren TL - Sci Rep (2014)

The theoretical model of the gate controlled GMH.(a) The schematic structure of the gate controlled GMH. The MoS2 is sandwiched between the graphene and the SiO2. (b) The Schottky barrier height obtained from different gate bias by solving the Poisson equation. Large (0.34 eV) Fermi level shift is obtained by −40 to 40 V gate control. (c) The simulations (Lines) and experiments (Points) of the FESBT. (d) Theoretical analysis showing that the subthreshold swing of FESBT overcomes the limitation of 60 mV/dec of conventional FET. (e) The mobility vs. the Vgate showing a maximum mobility of 58.7 cm2/V·s. The mobility is induced from the experimental results in Fig. 2c at 0.1 V bias. (f) The mobility vs. the Schottky barrier height showing that the maximum mobility is obtained at a barrier height of 0.26 eV.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4127518&req=5

f4: The theoretical model of the gate controlled GMH.(a) The schematic structure of the gate controlled GMH. The MoS2 is sandwiched between the graphene and the SiO2. (b) The Schottky barrier height obtained from different gate bias by solving the Poisson equation. Large (0.34 eV) Fermi level shift is obtained by −40 to 40 V gate control. (c) The simulations (Lines) and experiments (Points) of the FESBT. (d) Theoretical analysis showing that the subthreshold swing of FESBT overcomes the limitation of 60 mV/dec of conventional FET. (e) The mobility vs. the Vgate showing a maximum mobility of 58.7 cm2/V·s. The mobility is induced from the experimental results in Fig. 2c at 0.1 V bias. (f) The mobility vs. the Schottky barrier height showing that the maximum mobility is obtained at a barrier height of 0.26 eV.
Mentions: The graphene-MoS2 heterojunction is the core of FESBT devices. In order to fundamentally understand the physics of the heterojunction, a theoretical model is established. As illustrated in Figure 4a, the model consists of three parts: a Schottky junction formed by the GMH and two resistors connected with the source and drain terminals. The electrical performance of our device is mainly dependent on the heterojunction. In this case, the lateral transport is the dominant factor, suggesting that the resistance of this uniform junction is scaled with Ljunction/Wjunction. Therefore, the junction could also be regarded as an artificial thin film FET. These two resistors are included to consider the resistances of graphene and MoS2 between the junction and source/drain electrodes. Here MoS2 is considered as a thin bulk material, and the drop of electric potential in graphene is ignored since it has only several layers. The integral of electric field along the path perpendicular to the plane equals to the difference of work function between MoS2 and gate, assuming that the electric field is constant in graphene and MoS2, respectively. where , , , and Vch are the electric field, the thicknesses of the oxide and MoS2, the difference of the work functions between MoS2 and gate electrode, and the channel potential of graphene. The electric field is consistent at the interface between the oxide and the MoS2, where is the relative dielectric constant of the oxide and the MoS2. As the electric field penetrates into graphene, it induces free charges, so we obtain where e and n2D are electron charge and two-dimensional carrier density in graphene.

Bottom Line: Recently, two-dimensional materials such as molybdenum disulphide (MoS2) have been demonstrated to realize field effect transistors (FET) with a large current on-off ratio.Moreover, the field effective mobility of the FESBT is up to 58.7 cm(2)/V · s.Our theoretical analysis shows that if the thickness of oxide is further reduced, a subthreshold swing (SS) of 40 mV/decade can be maintained within three orders of drain current at room temperature.

View Article: PubMed Central - PubMed

Affiliation: 1] Institute of Microelectronics, Tsinghua University, Beijing 100084, China [2] Tsinghua National Laboratory for Information Science and Technology (TNList), Tsinghua University, Beijing 100084, China [3].

ABSTRACT
Recently, two-dimensional materials such as molybdenum disulphide (MoS2) have been demonstrated to realize field effect transistors (FET) with a large current on-off ratio. However, the carrier mobility in backgate MoS2 FET is rather low (typically 0.5-20 cm(2)/V · s). Here, we report a novel field-effect Schottky barrier transistors (FESBT) based on graphene-MoS2 heterojunction (GMH), where the characteristics of high mobility from graphene and high on-off ratio from MoS2 are properly balanced in the novel transistors. Large modulation on the device current (on/off ratio of 10(5)) is achieved by adjusting the backgate (through 300 nm SiO2) voltage to modulate the graphene-MoS2 Schottky barrier. Moreover, the field effective mobility of the FESBT is up to 58.7 cm(2)/V · s. Our theoretical analysis shows that if the thickness of oxide is further reduced, a subthreshold swing (SS) of 40 mV/decade can be maintained within three orders of drain current at room temperature. This provides an opportunity to overcome the limitation of 60 mV/decade for conventional CMOS devices. The FESBT implemented with a high on-off ratio, a relatively high mobility and a low subthreshold promises low-voltage and low-power applications for future electronics.

No MeSH data available.


Related in: MedlinePlus