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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

The performance of the multilayer WS2 nanoflakes as photodetector.(a) Drain-source (IDS-VDS) characteristic of the device based on the WS2 nanoflakes under the chopped red light illumination (633 nm, 30 mW/cm2). (b) Time-dependent photocurrent response during the light switching on/off at source drain voltage of 1.0 V. (c) Dynamic response characteristic of the device. The inset is corresponding to the rise (left) and decay (right) process. (d) Stability test of photo-switching behavior of the device with light switching on/off quickly and repetitively. (e) Source-drain (IDS-VDS) characteristics of the device under different incident optical power density from 0.1 to 62.8 mW/cm2 on a log scale. (f) “Output” characteristics of the device with light as “gating”.
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f3: The performance of the multilayer WS2 nanoflakes as photodetector.(a) Drain-source (IDS-VDS) characteristic of the device based on the WS2 nanoflakes under the chopped red light illumination (633 nm, 30 mW/cm2). (b) Time-dependent photocurrent response during the light switching on/off at source drain voltage of 1.0 V. (c) Dynamic response characteristic of the device. The inset is corresponding to the rise (left) and decay (right) process. (d) Stability test of photo-switching behavior of the device with light switching on/off quickly and repetitively. (e) Source-drain (IDS-VDS) characteristics of the device under different incident optical power density from 0.1 to 62.8 mW/cm2 on a log scale. (f) “Output” characteristics of the device with light as “gating”.

Mentions: Few- or monolayer MoS2 was demonstrated as ultrasensitive photodetectors based on the previous reports112243. In contrast to the widely studied MoS2 used for photodetectors, little attention has been paid to the 2D WS2. According to the above analysis, the multilayer WS2 nanoflakes can response to the visible light especially the red light with 633 nm since the energy of the red light approximates the band gap of WS2. Therefore, the photosensitive properties of the WS2 nanoflakes based photodetctors for the red light was measured systematically. Figure 3a shows the output characteristics under chopped red light irradiation with zero VG. The drain current can be modulated rapidly by the chopped light, and the current is significantly increased under the light irradiation compared to that in dark, implying a quick response to red light. As shown in Figure 3b, with light irradiation on/off, the device can work between low and high impedance states fast and reversibly with an on/off ratio (defined as Iphoto/Idark) of 25, allowing the device to act as a high quality photosensitive switch. The device also exhibits very fast dynamic response for both rise and decay process (Figure 3c), the response and recovery time is shorter than the detection limit of our measurement setup (20 ms), which is shorter than values for phototransistors based on monolayer MoS2 and hybrid graphene quantum dot2244, and it is also orders of magnitude shorter than the amorphous oxide semiconductors phototransistors45. Stability test of photo-switching behavior of the WS2 nanoflakes is also performed by switching the light on/off quickly and repetitively, accordingly the photocurrent of the device can change instantly between “ON” state and “OFF” state (Figure 3d). After hundreds of cycles, the photocurrent can still change with light switching on/off, displaying a high reversibility and stability of the device. Figure 3e shows the output characteristics under different light illumination densities. When the WS2 nanoflakes absorb the incident photons, large amounts of electron-pairs generate, forming like a conductive channel, and then being extracted by VDS to form the photocurrent. With increasing light density, the photocurrent is increased significantly. From the “output” characteristics shown in Figure 3f, our phototransistor can be open by the incident light of about 10 mW/cm2. So, like the electrical field effect, the incident light field can also act as a “gating” to modulate the density of carries in the source drain channel and make important effect on the electrical properties of the device.


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)

The performance of the multilayer WS2 nanoflakes as photodetector.(a) Drain-source (IDS-VDS) characteristic of the device based on the WS2 nanoflakes under the chopped red light illumination (633 nm, 30 mW/cm2). (b) Time-dependent photocurrent response during the light switching on/off at source drain voltage of 1.0 V. (c) Dynamic response characteristic of the device. The inset is corresponding to the rise (left) and decay (right) process. (d) Stability test of photo-switching behavior of the device with light switching on/off quickly and repetitively. (e) Source-drain (IDS-VDS) characteristics of the device under different incident optical power density from 0.1 to 62.8 mW/cm2 on a log scale. (f) “Output” characteristics of the device with light as “gating”.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: The performance of the multilayer WS2 nanoflakes as photodetector.(a) Drain-source (IDS-VDS) characteristic of the device based on the WS2 nanoflakes under the chopped red light illumination (633 nm, 30 mW/cm2). (b) Time-dependent photocurrent response during the light switching on/off at source drain voltage of 1.0 V. (c) Dynamic response characteristic of the device. The inset is corresponding to the rise (left) and decay (right) process. (d) Stability test of photo-switching behavior of the device with light switching on/off quickly and repetitively. (e) Source-drain (IDS-VDS) characteristics of the device under different incident optical power density from 0.1 to 62.8 mW/cm2 on a log scale. (f) “Output” characteristics of the device with light as “gating”.
Mentions: Few- or monolayer MoS2 was demonstrated as ultrasensitive photodetectors based on the previous reports112243. In contrast to the widely studied MoS2 used for photodetectors, little attention has been paid to the 2D WS2. According to the above analysis, the multilayer WS2 nanoflakes can response to the visible light especially the red light with 633 nm since the energy of the red light approximates the band gap of WS2. Therefore, the photosensitive properties of the WS2 nanoflakes based photodetctors for the red light was measured systematically. Figure 3a shows the output characteristics under chopped red light irradiation with zero VG. The drain current can be modulated rapidly by the chopped light, and the current is significantly increased under the light irradiation compared to that in dark, implying a quick response to red light. As shown in Figure 3b, with light irradiation on/off, the device can work between low and high impedance states fast and reversibly with an on/off ratio (defined as Iphoto/Idark) of 25, allowing the device to act as a high quality photosensitive switch. The device also exhibits very fast dynamic response for both rise and decay process (Figure 3c), the response and recovery time is shorter than the detection limit of our measurement setup (20 ms), which is shorter than values for phototransistors based on monolayer MoS2 and hybrid graphene quantum dot2244, and it is also orders of magnitude shorter than the amorphous oxide semiconductors phototransistors45. Stability test of photo-switching behavior of the WS2 nanoflakes is also performed by switching the light on/off quickly and repetitively, accordingly the photocurrent of the device can change instantly between “ON” state and “OFF” state (Figure 3d). After hundreds of cycles, the photocurrent can still change with light switching on/off, displaying a high reversibility and stability of the device. Figure 3e shows the output characteristics under different light illumination densities. When the WS2 nanoflakes absorb the incident photons, large amounts of electron-pairs generate, forming like a conductive channel, and then being extracted by VDS to form the photocurrent. With increasing light density, the photocurrent is increased significantly. From the “output” characteristics shown in Figure 3f, our phototransistor can be open by the incident light of about 10 mW/cm2. So, like the electrical field effect, the incident light field can also act as a “gating” to modulate the density of carries in the source drain channel and make important effect on the electrical properties of the device.

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