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Photoresponsive and gas sensing field-effect transistors based on multilayer WS₂ nanoflakes.

Huo N, Yang S, Wei Z, Li SS, Xia JB, Li J - Sci Rep (2014)

Bottom Line: The photoelectrical properties of multilayer WS₂ nanoflakes including field-effect, photosensitive and gas sensing are comprehensively and systematically studied.The ethanol and NH₃ molecules can serve as electron donors to enhance the Rλ and EQE significantly.Under the NH3 atmosphere, the maximum Rλ and EQE can even reach 884 A/W and 1.7 × 10(5)%, respectively.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of SciencesP.O. Box 912, Beijing 100083, China.

ABSTRACT
The photoelectrical properties of multilayer WS₂ nanoflakes including field-effect, photosensitive and gas sensing are comprehensively and systematically studied. The transistors perform an n-type behavior with electron mobility of 12 cm(2)/Vs and exhibit high photosensitive characteristics with response time (τ) of <20 ms, photo-responsivity (Rλ) of 5.7 A/W and external quantum efficiency (EQE) of 1118%. In addition, charge transfer can appear between the multilayer WS₂ nanoflakes and the physical-adsorbed gas molecules, greatly influencing the photoelectrical properties of our devices. The ethanol and NH₃ molecules can serve as electron donors to enhance the Rλ and EQE significantly. Under the NH3 atmosphere, the maximum Rλ and EQE can even reach 884 A/W and 1.7 × 10(5)%, respectively. This work demonstrates that multilayer WS₂ nanoflakes possess important potential for applications in field-effect transistors, highly sensitive photodetectors, and gas sensors, and it will open new way to develop two-dimensional (2D) WS₂-based optoelectronics.

No MeSH data available.


Related in: MedlinePlus

Field effect of the multilayer WS2 nanoflakes.(a) Output characteristics of the transistor based on multilayer WS2 nanoflakes using Au/Au as the drain/source electrodes. The inset is linear region at low source drain voltage. (b) Transfer characteristics of the device at a fixed VDS of 1 V on a log scale (left y axis) and on a linear scale (right y axis). All measurements were performed in air at room temperature with the absence of light. Output characteristics of the device with (c) white light (15 mW/cm2) from LEDs and (d) red light (633 nm, 15 mW/cm2) from red lasers. (e) Transfer characteristics of the devices in dark and under light illumination. (f) Output characteristics of the devices in dark with VDS ranging from 0 to 3 V.
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f2: Field effect of the multilayer WS2 nanoflakes.(a) Output characteristics of the transistor based on multilayer WS2 nanoflakes using Au/Au as the drain/source electrodes. The inset is linear region at low source drain voltage. (b) Transfer characteristics of the device at a fixed VDS of 1 V on a log scale (left y axis) and on a linear scale (right y axis). All measurements were performed in air at room temperature with the absence of light. Output characteristics of the device with (c) white light (15 mW/cm2) from LEDs and (d) red light (633 nm, 15 mW/cm2) from red lasers. (e) Transfer characteristics of the devices in dark and under light illumination. (f) Output characteristics of the devices in dark with VDS ranging from 0 to 3 V.

Mentions: Owing to the lack of dangling bonds, structural stability and high mobility40, 2D TMDCs were promising materials for FETs. To evaluate the electrical performance of the multilayer WS2 nanoflakes, the bottom-gated transistors on SiO2/Si were fabricated. Figure 2a and 2b show the typical output and transfer characteristics respectively, performing an n-type behavior. According to the previous reports4142, in the case of VG > VT and /VDS/ ≪ /VG − VT/, the FETs are turned on. The positive gate voltage (VG) can induce large amounts of electrons in the interfaces between the WS2 nanoflakes and SiO2 substrate, and a conducting channel is created which allows the current to flow between the source and drain. The FETs operate like a resistor and work at linear region, thus the source-drain current (IDS) can linearly depend of source-drain voltage (VDS) as shown in the inset of Figure 2a. In this case, the IDS and VDS can satisfy the formula , where L is channel length (20 μm), W is channel width (15 μm), and Ci is the gate capacitance which can be given by equation Ci = εoεr/d, εo (8.85 × 10−12 F/m) is vacuum dielectric constant, and εr (3.9) and d (300 nm) are dielectric constant and thickness of SiO2, respectively. The field-effect carrier mobility (μ) and threshold voltage (VT) of WS2 nanoflakes based FETs can be calculated from the linear region of the output properties by supplying the values of IDS and VDS at different VG into the above equation. We get that VT = −3.5 V, and the electrons mobility is up to 12 cm2/Vs. To estimate the intrinsic doping level of the prepared WS2 nanoflakes, IDS at zero VG was modeled as , where n2D is the 2D carrier concentration, q is the electron charge. From the output characteristics of WS2 nanoflakes (Figure 2a), n2D is extracted to be ~1.4 × 1011 cm−2. We have also performed Hall-effect measurements with four-probes on the WS2 nanoflakes to accurately determine μ and n2D, and the results are very similar with the field-effect μ and n2D (Figure S4).


Photoresponsive and gas sensing field-effect transistors based on multilayer WS₂ nanoflakes.

Huo N, Yang S, Wei Z, Li SS, Xia JB, Li J - Sci Rep (2014)

Field effect of the multilayer WS2 nanoflakes.(a) Output characteristics of the transistor based on multilayer WS2 nanoflakes using Au/Au as the drain/source electrodes. The inset is linear region at low source drain voltage. (b) Transfer characteristics of the device at a fixed VDS of 1 V on a log scale (left y axis) and on a linear scale (right y axis). All measurements were performed in air at room temperature with the absence of light. Output characteristics of the device with (c) white light (15 mW/cm2) from LEDs and (d) red light (633 nm, 15 mW/cm2) from red lasers. (e) Transfer characteristics of the devices in dark and under light illumination. (f) Output characteristics of the devices in dark with VDS ranging from 0 to 3 V.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4048886&req=5

f2: Field effect of the multilayer WS2 nanoflakes.(a) Output characteristics of the transistor based on multilayer WS2 nanoflakes using Au/Au as the drain/source electrodes. The inset is linear region at low source drain voltage. (b) Transfer characteristics of the device at a fixed VDS of 1 V on a log scale (left y axis) and on a linear scale (right y axis). All measurements were performed in air at room temperature with the absence of light. Output characteristics of the device with (c) white light (15 mW/cm2) from LEDs and (d) red light (633 nm, 15 mW/cm2) from red lasers. (e) Transfer characteristics of the devices in dark and under light illumination. (f) Output characteristics of the devices in dark with VDS ranging from 0 to 3 V.
Mentions: Owing to the lack of dangling bonds, structural stability and high mobility40, 2D TMDCs were promising materials for FETs. To evaluate the electrical performance of the multilayer WS2 nanoflakes, the bottom-gated transistors on SiO2/Si were fabricated. Figure 2a and 2b show the typical output and transfer characteristics respectively, performing an n-type behavior. According to the previous reports4142, in the case of VG > VT and /VDS/ ≪ /VG − VT/, the FETs are turned on. The positive gate voltage (VG) can induce large amounts of electrons in the interfaces between the WS2 nanoflakes and SiO2 substrate, and a conducting channel is created which allows the current to flow between the source and drain. The FETs operate like a resistor and work at linear region, thus the source-drain current (IDS) can linearly depend of source-drain voltage (VDS) as shown in the inset of Figure 2a. In this case, the IDS and VDS can satisfy the formula , where L is channel length (20 μm), W is channel width (15 μm), and Ci is the gate capacitance which can be given by equation Ci = εoεr/d, εo (8.85 × 10−12 F/m) is vacuum dielectric constant, and εr (3.9) and d (300 nm) are dielectric constant and thickness of SiO2, respectively. The field-effect carrier mobility (μ) and threshold voltage (VT) of WS2 nanoflakes based FETs can be calculated from the linear region of the output properties by supplying the values of IDS and VDS at different VG into the above equation. We get that VT = −3.5 V, and the electrons mobility is up to 12 cm2/Vs. To estimate the intrinsic doping level of the prepared WS2 nanoflakes, IDS at zero VG was modeled as , where n2D is the 2D carrier concentration, q is the electron charge. From the output characteristics of WS2 nanoflakes (Figure 2a), n2D is extracted to be ~1.4 × 1011 cm−2. We have also performed Hall-effect measurements with four-probes on the WS2 nanoflakes to accurately determine μ and n2D, and the results are very similar with the field-effect μ and n2D (Figure S4).

Bottom Line: The photoelectrical properties of multilayer WS₂ nanoflakes including field-effect, photosensitive and gas sensing are comprehensively and systematically studied.The ethanol and NH₃ molecules can serve as electron donors to enhance the Rλ and EQE significantly.Under the NH3 atmosphere, the maximum Rλ and EQE can even reach 884 A/W and 1.7 × 10(5)%, respectively.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of SciencesP.O. Box 912, Beijing 100083, China.

ABSTRACT
The photoelectrical properties of multilayer WS₂ nanoflakes including field-effect, photosensitive and gas sensing are comprehensively and systematically studied. The transistors perform an n-type behavior with electron mobility of 12 cm(2)/Vs and exhibit high photosensitive characteristics with response time (τ) of <20 ms, photo-responsivity (Rλ) of 5.7 A/W and external quantum efficiency (EQE) of 1118%. In addition, charge transfer can appear between the multilayer WS₂ nanoflakes and the physical-adsorbed gas molecules, greatly influencing the photoelectrical properties of our devices. The ethanol and NH₃ molecules can serve as electron donors to enhance the Rλ and EQE significantly. Under the NH3 atmosphere, the maximum Rλ and EQE can even reach 884 A/W and 1.7 × 10(5)%, respectively. This work demonstrates that multilayer WS₂ nanoflakes possess important potential for applications in field-effect transistors, highly sensitive photodetectors, and gas sensors, and it will open new way to develop two-dimensional (2D) WS₂-based optoelectronics.

No MeSH data available.


Related in: MedlinePlus