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Photothermoelectric and photovoltaic effects both present in MoS2.

Zhang Y, Li H, Wang L, Wang H, Xie X, Zhang SL, Liu R, Qiu ZJ - Sci Rep (2015)

Bottom Line: The generation and transport of photocurrent in multilayer MoS2 are found to differ from those in other low-dimensional materials that only contribute with either photovoltaic effect (PVE) or photothermoelectric effect (PTE).In multilayer MoS2, the PVE at the MoS2-metal interface dominates in the accumulation regime whereas the hot-carrier-assisted PTE prevails in the depletion regime.Besides, the anomalously large Seebeck coefficient observed in multilayer MoS2, which has also been reported by others, is caused by hot photo-excited carriers that are not in thermal equilibrium with the MoS2 lattice.

View Article: PubMed Central - PubMed

Affiliation: 1] State Key Laboratory of ASIC &System, School of Information Science and Technology, Fudan University, Shanghai 200433, China [2] State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem &Information Technology, Chinese Academy of Sciences, Changning Road 865, Shanghai 200050, China.

ABSTRACT
As a finite-energy-bandgap alternative to graphene, semiconducting molybdenum disulfide (MoS2) has recently attracted extensive interest for energy and sensor applications. In particular for broad-spectral photodetectors, multilayer MoS2 is more appealing than its monolayer counterpart. However, little is understood regarding the physics underlying the photoresponse of multilayer MoS2. Here, we employ scanning photocurrent microscopy to identify the nature of photocurrent generated in multilayer MoS2 transistors. The generation and transport of photocurrent in multilayer MoS2 are found to differ from those in other low-dimensional materials that only contribute with either photovoltaic effect (PVE) or photothermoelectric effect (PTE). In multilayer MoS2, the PVE at the MoS2-metal interface dominates in the accumulation regime whereas the hot-carrier-assisted PTE prevails in the depletion regime. Besides, the anomalously large Seebeck coefficient observed in multilayer MoS2, which has also been reported by others, is caused by hot photo-excited carriers that are not in thermal equilibrium with the MoS2 lattice.

No MeSH data available.


Related in: MedlinePlus

Electrical characteristics and photoswitching behavior of MoS2 transistor.(a) Transfer characteristics of the MoS2 transistor, measured at Vd = 1 V, with Vg sweeping in AP mode. (b) Stability of photoswitching behavior of the MoS2 transistor at Vd = 1 V and Vg = −15 V in AP mode. The laser spot was focused in the MoS2 channel with a laser power of 100 μW.
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f2: Electrical characteristics and photoswitching behavior of MoS2 transistor.(a) Transfer characteristics of the MoS2 transistor, measured at Vd = 1 V, with Vg sweeping in AP mode. (b) Stability of photoswitching behavior of the MoS2 transistor at Vd = 1 V and Vg = −15 V in AP mode. The laser spot was focused in the MoS2 channel with a laser power of 100 μW.

Mentions: Electrical characterization of our MoS2 FETs was performed in ambient environment. Similar to other low-dimensional devices without surface protection262728, MoS2 FETs are highly sensitive to extrinsic effects, especially adsorption of H2O/O2 from air2930. These effects can induce current hysteresis in transfer characteristics and electrical stress instability of MoS2 FETs when measured in conventional DC mode (Supplementary Fig. S1). The electrical instability can lead to persistent photoconductivity when switching on and off the laser illumination and therefore, a reduction of photoresponsivity with switching time (Supplementary Figs. S3 and S4). Therefore, stability of the device under electrical stress is a prerequisite for practical optoelectronic applications of MoS2. Recently, electrical characterization with Vg pulses of alternating polarities i.e. AP mode, has been reported to distinctively reduce the device instability compared to using DC mode283132. As shown in Supplementary Fig. S1 and Fig. 2a, the hysteresis of our MoS2 FETs is almost completely eliminated and stable electrical characteristics are obtained using the AP method. This method leads indeed to stable photoswitching behaviors when applying multiple illuminations (Fig. 2b and Supplementary Fig. S4), which can only be achieved in vacuum if MoS2 FETs are measured using the DC method33. Since the AP method is not based on any structural or chemical modification of the devices, as opposed to other measures employed to improve the device stability262934, it is of great potential in leading to more repeatable and clearly interpretable photo-sensing signals. Therefore, all our photoelectrical measurements were performed in AP mode in order to avoid additional stressing of the devices.


Photothermoelectric and photovoltaic effects both present in MoS2.

Zhang Y, Li H, Wang L, Wang H, Xie X, Zhang SL, Liu R, Qiu ZJ - Sci Rep (2015)

Electrical characteristics and photoswitching behavior of MoS2 transistor.(a) Transfer characteristics of the MoS2 transistor, measured at Vd = 1 V, with Vg sweeping in AP mode. (b) Stability of photoswitching behavior of the MoS2 transistor at Vd = 1 V and Vg = −15 V in AP mode. The laser spot was focused in the MoS2 channel with a laser power of 100 μW.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4300500&req=5

f2: Electrical characteristics and photoswitching behavior of MoS2 transistor.(a) Transfer characteristics of the MoS2 transistor, measured at Vd = 1 V, with Vg sweeping in AP mode. (b) Stability of photoswitching behavior of the MoS2 transistor at Vd = 1 V and Vg = −15 V in AP mode. The laser spot was focused in the MoS2 channel with a laser power of 100 μW.
Mentions: Electrical characterization of our MoS2 FETs was performed in ambient environment. Similar to other low-dimensional devices without surface protection262728, MoS2 FETs are highly sensitive to extrinsic effects, especially adsorption of H2O/O2 from air2930. These effects can induce current hysteresis in transfer characteristics and electrical stress instability of MoS2 FETs when measured in conventional DC mode (Supplementary Fig. S1). The electrical instability can lead to persistent photoconductivity when switching on and off the laser illumination and therefore, a reduction of photoresponsivity with switching time (Supplementary Figs. S3 and S4). Therefore, stability of the device under electrical stress is a prerequisite for practical optoelectronic applications of MoS2. Recently, electrical characterization with Vg pulses of alternating polarities i.e. AP mode, has been reported to distinctively reduce the device instability compared to using DC mode283132. As shown in Supplementary Fig. S1 and Fig. 2a, the hysteresis of our MoS2 FETs is almost completely eliminated and stable electrical characteristics are obtained using the AP method. This method leads indeed to stable photoswitching behaviors when applying multiple illuminations (Fig. 2b and Supplementary Fig. S4), which can only be achieved in vacuum if MoS2 FETs are measured using the DC method33. Since the AP method is not based on any structural or chemical modification of the devices, as opposed to other measures employed to improve the device stability262934, it is of great potential in leading to more repeatable and clearly interpretable photo-sensing signals. Therefore, all our photoelectrical measurements were performed in AP mode in order to avoid additional stressing of the devices.

Bottom Line: The generation and transport of photocurrent in multilayer MoS2 are found to differ from those in other low-dimensional materials that only contribute with either photovoltaic effect (PVE) or photothermoelectric effect (PTE).In multilayer MoS2, the PVE at the MoS2-metal interface dominates in the accumulation regime whereas the hot-carrier-assisted PTE prevails in the depletion regime.Besides, the anomalously large Seebeck coefficient observed in multilayer MoS2, which has also been reported by others, is caused by hot photo-excited carriers that are not in thermal equilibrium with the MoS2 lattice.

View Article: PubMed Central - PubMed

Affiliation: 1] State Key Laboratory of ASIC &System, School of Information Science and Technology, Fudan University, Shanghai 200433, China [2] State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem &Information Technology, Chinese Academy of Sciences, Changning Road 865, Shanghai 200050, China.

ABSTRACT
As a finite-energy-bandgap alternative to graphene, semiconducting molybdenum disulfide (MoS2) has recently attracted extensive interest for energy and sensor applications. In particular for broad-spectral photodetectors, multilayer MoS2 is more appealing than its monolayer counterpart. However, little is understood regarding the physics underlying the photoresponse of multilayer MoS2. Here, we employ scanning photocurrent microscopy to identify the nature of photocurrent generated in multilayer MoS2 transistors. The generation and transport of photocurrent in multilayer MoS2 are found to differ from those in other low-dimensional materials that only contribute with either photovoltaic effect (PVE) or photothermoelectric effect (PTE). In multilayer MoS2, the PVE at the MoS2-metal interface dominates in the accumulation regime whereas the hot-carrier-assisted PTE prevails in the depletion regime. Besides, the anomalously large Seebeck coefficient observed in multilayer MoS2, which has also been reported by others, is caused by hot photo-excited carriers that are not in thermal equilibrium with the MoS2 lattice.

No MeSH data available.


Related in: MedlinePlus