High-speed scanning photocurrent imaging techniques on nanoscale devices

Park, J.K.; Son, Byung Hee; Park, Jiyong; Lee, Soonil; Ahn, Y. H.

doi:10.1016/j.cap.2013.08.019

Cited by 8 publications

(12 citation statements)

References 24 publications

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“…The carrier diffusion motions induced by a pump pulse located in the middle of the NWs were visualized; however, these optical measurements are limited for interrogating the carrier dynamics in operating devices because they strongly depend on the non-linear properties of materials and they are frequently obscured by the substrate signals. Consequently, these techniques are not ideal for low-dimensional systems with NWs thinner than the optical spot size (<100 nm) or with SWNTs.Scanning photocurrent microscopy (SPCM) techniques have been introduced as powerful tools for investigating local optoelectronic characteristics, such as metallic contacts, defects, interfaces, and junctions [12][13][14][15][16][17][18][19] . We were able to collect localized electronic band information that is not disturbed by signals originating from the substrate, and hence, compared with conventional optical pump-probe techniques, SPCM can provide a higher signal-to-noise ratio.…”

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confidence: 99%

“…Scanning photocurrent microscopy (SPCM) techniques have been introduced as powerful tools for investigating local optoelectronic characteristics, such as metallic contacts, defects, interfaces, and junctions [12][13][14][15][16][17][18][19] . We were able to collect localized electronic band information that is not disturbed by signals originating from the substrate, and hence, compared with conventional optical pump-probe techniques, SPCM can provide a higher signal-to-noise ratio.…”

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confidence: 99%

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Imaging Ultrafast Carrier Transport in Nanoscale Field-Effect Transistors

et al. 2014

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One-dimensional nanoscale devices, such as semiconductor nanowires (NWs) and singlewalled carbon nanotubes (SWNTs), have been intensively investigated because of their potential application of future high-speed electronic, optoelectronic, and sensing devices 1-3 .To overcome current limitations on the speed of contemporary devices, investigation of charge carrier dynamics with an ultrashort time scale is one of the primary steps necessary for developing high-speed devices. In the present study, we visualize ultrafast carrier dynamics in nanoscale devices using a combination of scanning photocurrent microscopy and timeresolved pump-probe techniques. We investigate transit times of carriers that are generated near one metallic electrode and subsequently transported toward the opposite electrode based on drift and diffusion motions. Carrier dynamics have been measured for various working conditions. In particular, the carrier velocities extracted from transit times increase for a larger negative gate bias, because of the increased field strength at the Schottky barrier. *Electronic mail: ahny@ajou.ac.kr 2The transit time of the charge carriers is a crucial factor limiting the high frequency response of nanoscale devices; however, traditional radio-frequency measurements are often limited by the high impedance or the RC constants of the devices [4][5][6][7][8] . Alternatively, optical ultrafast measurement techniques have been widely used to investigate charge carrier dynamics with a time resolution determined by the optical pulse width (down to a few femtoseconds) 9 . Recently, researchers have reported visualizing charge carrier movements in free-standing Si NWs using an ultrafast pump-probe imaging technique 10,11 . The carrier diffusion motions induced by a pump pulse located in the middle of the NWs were visualized; however, these optical measurements are limited for interrogating the carrier dynamics in operating devices because they strongly depend on the non-linear properties of materials and they are frequently obscured by the substrate signals. Consequently, these techniques are not ideal for low-dimensional systems with NWs thinner than the optical spot size (<100 nm) or with SWNTs.Scanning photocurrent microscopy (SPCM) techniques have been introduced as powerful tools for investigating local optoelectronic characteristics, such as metallic contacts, defects, interfaces, and junctions [12][13][14][15][16][17][18][19] . We were able to collect localized electronic band information that is not disturbed by signals originating from the substrate, and hence, compared with conventional optical pump-probe techniques, SPCM can provide a higher signal-to-noise ratio. Only recently, ultrafast pump-probe photocurrent techniques have been demonstrated for studying carrier dynamics in carbon nanotube devices by using a collinear pump and probe beams, focused at the same position 20,21 . In addition, ultrafast phenomena in graphene and GaAs NWs have been investigated by measuring terahertz radiation that results from...

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Imaging Ultrafast Carrier Transport in Nanoscale Field-Effect Transistors

et al. 2014

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“…7,11,[18][19][20][21][22][23][24] Since the SPCM signal originates from local electric fields, the position, intensity, and shape of the signals provide detailed information regarding the electric potential profiles of the devices, as has been discussed elsewhere. 11,12,25 Additionally, SPCM methods are based on optical probing techniques that can deliver optoelectronic information in a non-contact and non-destructive manner. Therefore, they can serve as a powerful tool for addressing the localized electronic states in SWNTs and NWs in aqueous environments without noticeably disturbing the device operation.…”

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confidence: 99%

“…In this setup, the individual SWNT devices are illuminated using a diffraction-limited laser focal spot, while the electric current is recorded as a function of the laser spot position, as has been discussed previously. 12,26,27 To address the device operation in an aqueous environment, we used a water-immersion type objective lens (60Â, N.A 0.9), whereas for measurements in ambient conditions, we used a conventional objective lens (100Â, N.A 0.8). The focused laser was scanned using galvanometer scanning mirrors.…”

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Imaging surface charge distribution near carbon nanotube device in aqueous environments

Park

Son

Park

et al. 2014

Applied Physics Letters

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In this paper, we demonstrate the scanning photocurrent imaging on carbon nanotube devices in high-purity water environments. We found a streak of photocurrent signals along the nanotube devices; these streaks help in locating individual nanotubes. The photocurrent signals appearing in the middle of the nanotubes are due to the presence of additional ions in the electrical double layer, and as a result, a nanotube device can be used to sense the charge distribution at water-substrate interfaces with nanometer resolution. The gate-dependent photocurrent signals allow us to enumerate the effective charge density influencing nanotube electric potentials. We monitored the dynamical change in the charge distribution, which originates from the dissolution of carbon dioxide from the atmosphere into the solutions.

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“…As schematically shown in Fig. 1 , we scanned the focused UV laser (2.8 mW) over the samples, while simultaneously monitoring the photo-induced signals as a function of the laser’s position 26 – 29 . To address the device operation in an electrolyte environment, we used a water-immersion type objective lens (Supplementary Information S1 ) 32 .…”

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Electronic Band Alignment at Complex Oxide Interfaces Measured by Scanning Photocurrent Microscopy

Yoon

Jung

Hong

et al. 2017

Sci Rep

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The band alignment at an Al2O3/SrTiO3 heterointerface forming a two-dimensional electron gas (2DEG) was investigated using scanning photocurrent microscopy (SPCM) in an electrolyte-gated environment. We used a focused UV laser source for above-the-bandgap illumination on the SrTiO3 layer, creating electron-hole pairs that contributed to the photocurrent through migration towards the metal electrodes. The polarity of the SPCM signals of a bare SrTiO3 device shows typical p-type behavior at zero gate bias, in which the photogenerated electrons are collected by the electrodes. In contrast, the SPCM polarity of 2DEG device indicates that the hole carriers were collected by the metal electrodes. Careful transport measurements revealed that the gate-dependent conductance of the 2DEG devices exhibits n-type switching behavior. More importantly, the SPCM signals in 2DEG devices demonstrated very unique gate-responses that cannot be found in conventional semiconducting devices, based on which we were able to perform detailed investigation into the electronic band alignment of the 2DEG devices and obtain the valence band offset at the heterointerface.

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High-speed scanning photocurrent imaging techniques on nanoscale devices

Cited by 8 publications

References 24 publications

Imaging Ultrafast Carrier Transport in Nanoscale Field-Effect Transistors

Imaging Ultrafast Carrier Transport in Nanoscale Field-Effect Transistors

Imaging surface charge distribution near carbon nanotube device in aqueous environments

Electronic Band Alignment at Complex Oxide Interfaces Measured by Scanning Photocurrent Microscopy

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