Limits...
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

Gas sensing and its effect on photoresponse.(a) IDS-VDS characteristics (on a log scale of y-axis) of the WS2 nanoflakes photodetectors under dark or in the presence of light (633 nm, 30 mW/cm2) measured in air and in vacuum. The insert is corresponding curve on a linear scale of y axis. (b) Time-dependent photocurrent response under air and vacuum during the light switching on/off. (c) IDS-VDS characteristics (on a log scale of y-axis) of the device under dark or in the presence of light (633 nm, 40 mW/cm2) measured in various gas atmospheres. The inset is corresponding curves on a linear scale of y axis. (d) Time-dependent photocurrent response under various gas atmospheres. (e) The extracted dark current and photocurrent under different gas atmospheres. (f) Schematic diagram of charge transfer process between adsorbed gas molecules and the multilayer WS2 nanoflakes transistor. (g) The gas sensitivity (A) (defined as S = /(Igas − Ivacuum)/Ivacuum/) and current change (B) (defined as ΔI = /Igas − Ivacuum/) under different conditions. (h) The photo-responsivity Rλ under various gas atmospheres, showing high sensitivity. The device exhibits a maximum Rλ of 884 A/W with low light density of 50 μW/cm2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4048886&req=5

f4: Gas sensing and its effect on photoresponse.(a) IDS-VDS characteristics (on a log scale of y-axis) of the WS2 nanoflakes photodetectors under dark or in the presence of light (633 nm, 30 mW/cm2) measured in air and in vacuum. The insert is corresponding curve on a linear scale of y axis. (b) Time-dependent photocurrent response under air and vacuum during the light switching on/off. (c) IDS-VDS characteristics (on a log scale of y-axis) of the device under dark or in the presence of light (633 nm, 40 mW/cm2) measured in various gas atmospheres. The inset is corresponding curves on a linear scale of y axis. (d) Time-dependent photocurrent response under various gas atmospheres. (e) The extracted dark current and photocurrent under different gas atmospheres. (f) Schematic diagram of charge transfer process between adsorbed gas molecules and the multilayer WS2 nanoflakes transistor. (g) The gas sensitivity (A) (defined as S = /(Igas − Ivacuum)/Ivacuum/) and current change (B) (defined as ΔI = /Igas − Ivacuum/) under different conditions. (h) The photo-responsivity Rλ under various gas atmospheres, showing high sensitivity. The device exhibits a maximum Rλ of 884 A/W with low light density of 50 μW/cm2.

Mentions: Previous reports showed that the photoelectrical response properties were strongly affected by gas environment for the MoS2 monolayer-based phototransistors43. We also performed the photosensitive measurements of our devices in ambient air and under vacuum. The drain current under vacuum is higher than that in ambient air under both dark and light (Figure 4a), and the increment of current is more obvious under light illumination shown in the inset. Moreover, the photosensitivity is also enhanced under vacuum (Figure 4b). Density functional theory (DFT) calculations12 discover that the O2 and H2O molecules can interact weakly to the TMDCs monolayer with binding energies ranging from 70 to 140 meV and substantial electrons can transfer into the physical-adsorbed gas molecules from the semiconductors. Large amounts of O2 and H2O molecules exist in air and the WS2 nanoflakes display n-type behavior from the above Hall and field-effect results. In our case, O2 and H2O molecules in ambient air can be physically adsorbed on the surface of the WS2 nanoflakes and withdraw numerous electrons from WS2, depleting the n-type of WS2 nanoflakes. Thus the resistance becomes larger due to the reduction of major conduction electrons, corresponding to the reduced IDS. Upon light illumination in air, much electron-hole pairs generate and the density of electrons in the WS2 nanoflakes is improved as discussed above. O2 and H2O molecules as electron acceptors will have more electrons to accept, corresponding to more gas molecules in ambient can be adsorbed and deplete more electrons, leading to the decreased photosensitivity. Moreover, the photocurrent shows a strong dependence on light intensity and the experimental data are fitted by a power equation Iph = aPα, where a is scaling constant, and α is exponent. Under vacuum, the photocurrent displays a power dependence of ~0.91 (function: Iph = 0.26P0.91) as shown in Figure S5a, indicating a superior photocurrent capability and a high efficiency of photo-generated charge carriers from the absorbed photons. However, the exponent α in air (function: Iph = 0.52P0.73) shown in Figure S5b is smaller than that under vacuum, indicating the route of the loss of the photo-exited carrier by the adsorbed O2 or H2O molecules in air. Similar phenomenon is also observed in MoS2-based phototransistor43.


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)

Gas sensing and its effect on photoresponse.(a) IDS-VDS characteristics (on a log scale of y-axis) of the WS2 nanoflakes photodetectors under dark or in the presence of light (633 nm, 30 mW/cm2) measured in air and in vacuum. The insert is corresponding curve on a linear scale of y axis. (b) Time-dependent photocurrent response under air and vacuum during the light switching on/off. (c) IDS-VDS characteristics (on a log scale of y-axis) of the device under dark or in the presence of light (633 nm, 40 mW/cm2) measured in various gas atmospheres. The inset is corresponding curves on a linear scale of y axis. (d) Time-dependent photocurrent response under various gas atmospheres. (e) The extracted dark current and photocurrent under different gas atmospheres. (f) Schematic diagram of charge transfer process between adsorbed gas molecules and the multilayer WS2 nanoflakes transistor. (g) The gas sensitivity (A) (defined as S = /(Igas − Ivacuum)/Ivacuum/) and current change (B) (defined as ΔI = /Igas − Ivacuum/) under different conditions. (h) The photo-responsivity Rλ under various gas atmospheres, showing high sensitivity. The device exhibits a maximum Rλ of 884 A/W with low light density of 50 μW/cm2.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Gas sensing and its effect on photoresponse.(a) IDS-VDS characteristics (on a log scale of y-axis) of the WS2 nanoflakes photodetectors under dark or in the presence of light (633 nm, 30 mW/cm2) measured in air and in vacuum. The insert is corresponding curve on a linear scale of y axis. (b) Time-dependent photocurrent response under air and vacuum during the light switching on/off. (c) IDS-VDS characteristics (on a log scale of y-axis) of the device under dark or in the presence of light (633 nm, 40 mW/cm2) measured in various gas atmospheres. The inset is corresponding curves on a linear scale of y axis. (d) Time-dependent photocurrent response under various gas atmospheres. (e) The extracted dark current and photocurrent under different gas atmospheres. (f) Schematic diagram of charge transfer process between adsorbed gas molecules and the multilayer WS2 nanoflakes transistor. (g) The gas sensitivity (A) (defined as S = /(Igas − Ivacuum)/Ivacuum/) and current change (B) (defined as ΔI = /Igas − Ivacuum/) under different conditions. (h) The photo-responsivity Rλ under various gas atmospheres, showing high sensitivity. The device exhibits a maximum Rλ of 884 A/W with low light density of 50 μW/cm2.
Mentions: Previous reports showed that the photoelectrical response properties were strongly affected by gas environment for the MoS2 monolayer-based phototransistors43. We also performed the photosensitive measurements of our devices in ambient air and under vacuum. The drain current under vacuum is higher than that in ambient air under both dark and light (Figure 4a), and the increment of current is more obvious under light illumination shown in the inset. Moreover, the photosensitivity is also enhanced under vacuum (Figure 4b). Density functional theory (DFT) calculations12 discover that the O2 and H2O molecules can interact weakly to the TMDCs monolayer with binding energies ranging from 70 to 140 meV and substantial electrons can transfer into the physical-adsorbed gas molecules from the semiconductors. Large amounts of O2 and H2O molecules exist in air and the WS2 nanoflakes display n-type behavior from the above Hall and field-effect results. In our case, O2 and H2O molecules in ambient air can be physically adsorbed on the surface of the WS2 nanoflakes and withdraw numerous electrons from WS2, depleting the n-type of WS2 nanoflakes. Thus the resistance becomes larger due to the reduction of major conduction electrons, corresponding to the reduced IDS. Upon light illumination in air, much electron-hole pairs generate and the density of electrons in the WS2 nanoflakes is improved as discussed above. O2 and H2O molecules as electron acceptors will have more electrons to accept, corresponding to more gas molecules in ambient can be adsorbed and deplete more electrons, leading to the decreased photosensitivity. Moreover, the photocurrent shows a strong dependence on light intensity and the experimental data are fitted by a power equation Iph = aPα, where a is scaling constant, and α is exponent. Under vacuum, the photocurrent displays a power dependence of ~0.91 (function: Iph = 0.26P0.91) as shown in Figure S5a, indicating a superior photocurrent capability and a high efficiency of photo-generated charge carriers from the absorbed photons. However, the exponent α in air (function: Iph = 0.52P0.73) shown in Figure S5b is smaller than that under vacuum, indicating the route of the loss of the photo-exited carrier by the adsorbed O2 or H2O molecules in air. Similar phenomenon is also observed in MoS2-based phototransistor43.

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