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Ultrafast response of monolayer molybdenum disulfide photodetectors.

Wang H, Zhang C, Chan W, Tiwari S, Rana F - Nat Commun (2015)

Bottom Line: In this work, using two-pulse photovoltage correlation technique, we show that monolayer molybdenum disulfide photodetector can have intrinsic response times as short as 3 ps implying photodetection bandwidths as wide as 300 GHz.The fast photodetector response is a result of the short electron-hole and exciton lifetimes in this material.The fast response time, and the ease of fabrication of these devices, make them interesting for low-cost ultrafast optical communication links.

View Article: PubMed Central - PubMed

Affiliation: School of Electrical and Computer Engineering, Cornell University, Ithaca 14853, New York, USA.

ABSTRACT
The strong light emission and absorption exhibited by single atomic layer transitional metal dichalcogenides in the visible to near-infrared wavelength range make them attractive for optoelectronic applications. In this work, using two-pulse photovoltage correlation technique, we show that monolayer molybdenum disulfide photodetector can have intrinsic response times as short as 3 ps implying photodetection bandwidths as wide as 300 GHz. The fast photodetector response is a result of the short electron-hole and exciton lifetimes in this material. Recombination of photoexcited carriers in most two-dimensional metal dichalcogenides is dominated by nonradiative processes, most notable among which is Auger scattering. The fast response time, and the ease of fabrication of these devices, make them interesting for low-cost ultrafast optical communication links.

No MeSH data available.


TPPC experiment and circuit model of metal-MoS2 photodetector.(a) Optical micrograph of a fabricated back-gated monolayer metal-MoS2 photodetector on SiO2/Si substrate is shown. (b) A schematic of the two-pulse photovoltage correlation (TPPC) experiment is shown. Two time-delayed 452 nm optical pulses, both obtained via upconversion from a single Ti:Sapphire laser, are focused at one of the metal-semiconductor Schottky junctions. The generated d.c. photovoltage is recorded as a function of the time delay between the pulses. A lock-in detection scheme is used to improve the signal-to-noise ratio. The arrow indicates the positive direction of the photocurrent (and the sign of the measured photovoltage) form the illuminated metal contact. (c) A low-frequency circuit model of the device and measurement. The current source I2(t, Δt) represents the short circuit current response of the junction in response to two optical pulses separated by time Δt. Rj is the resistance of the metal-MoS2 junction.  is the resistance of the MoS2 layer. Rext is the external circuit resistance (including the ∼10 MΩ input resistance of the measurement instrument).
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f1: TPPC experiment and circuit model of metal-MoS2 photodetector.(a) Optical micrograph of a fabricated back-gated monolayer metal-MoS2 photodetector on SiO2/Si substrate is shown. (b) A schematic of the two-pulse photovoltage correlation (TPPC) experiment is shown. Two time-delayed 452 nm optical pulses, both obtained via upconversion from a single Ti:Sapphire laser, are focused at one of the metal-semiconductor Schottky junctions. The generated d.c. photovoltage is recorded as a function of the time delay between the pulses. A lock-in detection scheme is used to improve the signal-to-noise ratio. The arrow indicates the positive direction of the photocurrent (and the sign of the measured photovoltage) form the illuminated metal contact. (c) A low-frequency circuit model of the device and measurement. The current source I2(t, Δt) represents the short circuit current response of the junction in response to two optical pulses separated by time Δt. Rj is the resistance of the metal-MoS2 junction. is the resistance of the MoS2 layer. Rext is the external circuit resistance (including the ∼10 MΩ input resistance of the measurement instrument).

Mentions: Microscope image of a monolayer metal-MoS2 photodetector is shown in Fig. 1a, and the schematic in Fig. 1b depicts the setup for a TPPC experiment. A ∼80-fs, 905-nm (1.37 eV) centre wavelength, optical pulse from a ∼83-MHz repetition rate Ti–Sapphire laser is frequency doubled to 452 nm (2.74 eV, ∼150 fs) by a beta-BaB2O4 crystal, then mechanically chopped at 1.73 KHz and then split into two pulses by a 50/50 beam splitter. The time delay Δt between these two pulses is controlled by a linear translation stage. The resulting voltage across the photodetector is measured as a function of the time delay between the pulses using a lock-in amplifier with a 10 MΩ input resistance. In experiments, the maximum photoresponse was obtained when the light was focused on the sample near one of the metal contacts of the device, and the photoresponse decayed rapidly as the centre of the focus spot was moved more than half a micron away from the metal contact. The direction of the d.c. photocurrent, and the resulting sign of the measured d.c. photovoltage are shown in Fig. 1b, and were determined without using the lock-in. Photovoltage was always positive at the contact near which the light was focused. Figure 1c shows a low-frequency circuit model of the device and the measurement. The circuit model shown can be derived from a high-frequency circuit model (Supplementary Fig. 2 and Supplementary Note 3). If the time-dependent short circuit current response of the illuminated junction to a single optical pulse is I1(t), and to two optical pulses separated by time Δt is I2(t, Δt), and the external resistance Rext is much larger than the total device resistance, then the measured d.c. voltage Vc(Δt) is approximately equal to (Rj/TR)∫I2(t, Δt)dt, where TR is the pulse repetition period, Rj is the resistance of the metal-MoS2 junction, and the time integral is over one complete period. As the time delay Δt becomes much longer than the duration of I1(t), one expects Vc(Δt) to approach (2Rj/TR)∫I1(t)dt.


Ultrafast response of monolayer molybdenum disulfide photodetectors.

Wang H, Zhang C, Chan W, Tiwari S, Rana F - Nat Commun (2015)

TPPC experiment and circuit model of metal-MoS2 photodetector.(a) Optical micrograph of a fabricated back-gated monolayer metal-MoS2 photodetector on SiO2/Si substrate is shown. (b) A schematic of the two-pulse photovoltage correlation (TPPC) experiment is shown. Two time-delayed 452 nm optical pulses, both obtained via upconversion from a single Ti:Sapphire laser, are focused at one of the metal-semiconductor Schottky junctions. The generated d.c. photovoltage is recorded as a function of the time delay between the pulses. A lock-in detection scheme is used to improve the signal-to-noise ratio. The arrow indicates the positive direction of the photocurrent (and the sign of the measured photovoltage) form the illuminated metal contact. (c) A low-frequency circuit model of the device and measurement. The current source I2(t, Δt) represents the short circuit current response of the junction in response to two optical pulses separated by time Δt. Rj is the resistance of the metal-MoS2 junction.  is the resistance of the MoS2 layer. Rext is the external circuit resistance (including the ∼10 MΩ input resistance of the measurement instrument).
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4660040&req=5

f1: TPPC experiment and circuit model of metal-MoS2 photodetector.(a) Optical micrograph of a fabricated back-gated monolayer metal-MoS2 photodetector on SiO2/Si substrate is shown. (b) A schematic of the two-pulse photovoltage correlation (TPPC) experiment is shown. Two time-delayed 452 nm optical pulses, both obtained via upconversion from a single Ti:Sapphire laser, are focused at one of the metal-semiconductor Schottky junctions. The generated d.c. photovoltage is recorded as a function of the time delay between the pulses. A lock-in detection scheme is used to improve the signal-to-noise ratio. The arrow indicates the positive direction of the photocurrent (and the sign of the measured photovoltage) form the illuminated metal contact. (c) A low-frequency circuit model of the device and measurement. The current source I2(t, Δt) represents the short circuit current response of the junction in response to two optical pulses separated by time Δt. Rj is the resistance of the metal-MoS2 junction. is the resistance of the MoS2 layer. Rext is the external circuit resistance (including the ∼10 MΩ input resistance of the measurement instrument).
Mentions: Microscope image of a monolayer metal-MoS2 photodetector is shown in Fig. 1a, and the schematic in Fig. 1b depicts the setup for a TPPC experiment. A ∼80-fs, 905-nm (1.37 eV) centre wavelength, optical pulse from a ∼83-MHz repetition rate Ti–Sapphire laser is frequency doubled to 452 nm (2.74 eV, ∼150 fs) by a beta-BaB2O4 crystal, then mechanically chopped at 1.73 KHz and then split into two pulses by a 50/50 beam splitter. The time delay Δt between these two pulses is controlled by a linear translation stage. The resulting voltage across the photodetector is measured as a function of the time delay between the pulses using a lock-in amplifier with a 10 MΩ input resistance. In experiments, the maximum photoresponse was obtained when the light was focused on the sample near one of the metal contacts of the device, and the photoresponse decayed rapidly as the centre of the focus spot was moved more than half a micron away from the metal contact. The direction of the d.c. photocurrent, and the resulting sign of the measured d.c. photovoltage are shown in Fig. 1b, and were determined without using the lock-in. Photovoltage was always positive at the contact near which the light was focused. Figure 1c shows a low-frequency circuit model of the device and the measurement. The circuit model shown can be derived from a high-frequency circuit model (Supplementary Fig. 2 and Supplementary Note 3). If the time-dependent short circuit current response of the illuminated junction to a single optical pulse is I1(t), and to two optical pulses separated by time Δt is I2(t, Δt), and the external resistance Rext is much larger than the total device resistance, then the measured d.c. voltage Vc(Δt) is approximately equal to (Rj/TR)∫I2(t, Δt)dt, where TR is the pulse repetition period, Rj is the resistance of the metal-MoS2 junction, and the time integral is over one complete period. As the time delay Δt becomes much longer than the duration of I1(t), one expects Vc(Δt) to approach (2Rj/TR)∫I1(t)dt.

Bottom Line: In this work, using two-pulse photovoltage correlation technique, we show that monolayer molybdenum disulfide photodetector can have intrinsic response times as short as 3 ps implying photodetection bandwidths as wide as 300 GHz.The fast photodetector response is a result of the short electron-hole and exciton lifetimes in this material.The fast response time, and the ease of fabrication of these devices, make them interesting for low-cost ultrafast optical communication links.

View Article: PubMed Central - PubMed

Affiliation: School of Electrical and Computer Engineering, Cornell University, Ithaca 14853, New York, USA.

ABSTRACT
The strong light emission and absorption exhibited by single atomic layer transitional metal dichalcogenides in the visible to near-infrared wavelength range make them attractive for optoelectronic applications. In this work, using two-pulse photovoltage correlation technique, we show that monolayer molybdenum disulfide photodetector can have intrinsic response times as short as 3 ps implying photodetection bandwidths as wide as 300 GHz. The fast photodetector response is a result of the short electron-hole and exciton lifetimes in this material. Recombination of photoexcited carriers in most two-dimensional metal dichalcogenides is dominated by nonradiative processes, most notable among which is Auger scattering. The fast response time, and the ease of fabrication of these devices, make them interesting for low-cost ultrafast optical communication links.

No MeSH data available.