Research

Scanning Photocurrent Microscopy on Nanoscale Devices

Scanning photocurrent microscopy (SPCM) uses a focused light beam as a local excitation source to generate a photocurrent and maps the measured current signal as a function of position in a non-contact and non-destructive manner. Since the SPCM signal originates from local electric fields, the position, intensity, and the shape of the signal provide detailed information regarding the presence of metal contacts, local defects, inhomogeneities, junctions, and interfaces.



Related articles:
  • Electronic Band Alignment at Complex Oxide Interfaces Measured by Scanning Photocurrent Microscopy
    Scientific Reports 7, 3824 (2017); DOI: 10.1038/s41598-017-04265-9
    J. H. Yoon, H. J. Jung, J. T. Hong, J. Y. Park, S. Lee, S. W. Lee, Y. H. Ahn

  • Imaging surface charge distribution near carbon nanotube device in aqueous environments
    Appl. Phys. Lett. 105, 223101 (2014); DOI: 10.1063/1.4902401; featured (cover) article
    J. K. Park, B. H. Son, J. Y. Park, S. Lee, Y. H. Ahn

  • High-speed scanning photocurrent imaging techniques on nanoscale devices
    Curr. Appl. Phys.13 2076 (2013); DOI: 10.1016/j.cap.2013.08.019
    J. K. Park, B. H. Son, J. Y. Park, S. Lee, Y. H. Ahn

  • Imaging of Photocurrent Generation and Collection in Single-Layer Graphene
    Nano Lett. 9, 1742 (2009)
    J. Park, Y. H. Ahn, C. Ruiz-Vargas

  • Photocurrent Imaging of p-n Junctions in Ambipolar Carbon Nanotube Transistors
    Nano Lett. 7, 3320 (2007)
    Y. H. Ahn, A. W. Tsen, B. Kim, Y. W. Park, J. Park

 




Solar Cell Characterization

The carrier diffusion lengths in semiconductor electrode layers of solar cells can be determined by using scanning photocurrent microscopy. We found a strong correlation between the carrier diffusion length and the cell efficiency, which proved that improvement in the diffusion length is the crucial factors for optimizing device performance. Our work will provide an important guideline for optimizing various contemporary and future photovoltaic devices based on the nanoscale materials and structures.


Related articles:

  • Crystallization Kinetics of Lead Halide Perovskite Film Monitored by In Situ Terahertz Spectroscopy
    J. Phys. Chem. Lett. 8, 401 (2017); DOI: 10.1021/acs.jpclett.6b02691
    S. J. Park, A. R. Kim, J. T. Hong, J. Y. Park, S. Lee, Y. H. Ahn

  • Diffusion Length in Nanoporous Photoelectrodes of Dye-Sensitized Solar Cells under Operating Conditions Measured by Photocurrent Microscopy
    J. Phys. Chem. Lett. 3, 3632 (2012); DOI: 10.1021/jz301751j
    J.-K. Park, J.-C. Kang, S. Y. Kim, B. H. Son, J.-Y. Park, S. Lee, Y. H. Ahn

  • Diffusion Length in Nanoporous TiO2 Films under Above-Band-Gap Illumination
    AIP. Adv. 4, 067106 (2014); DOI: 10.1063/1.4881875
    J. D. Park, B. H. Son, J. K. Park, S. Y. Kim, J. Y. Park, S. Lee, Y. H. Ahn

 

Ultrafast Scanning Photocurrent Microscopy

Ultrafast Scanning Photocurrent Microscopy, which is combined scanning photocurrent microscopy and femtosecond (10-15 second) pump-probe optical techniques, can be used for visualization of the charge carrier movement inside the working semiconductor devices. This information will provide an important guideline to fabricate high-speed electronic and optoelectronic devices.

Related article:

  • Imaging Ultrafast Carrier Transport in Nanoscale Field-Effect Transistors
    ACS Nano  8, 11361 (2014); DOI: 10.1021/nn5042619; SPIE newsroom
    B. H. Son, J. K. Park, J. T. Hong, J. Y. Park, S. Lee, Y. H. Ahn

 

Terahertz Biosensor

Nowadays, we are researching the terahertz (THz) metamaterial and plasmonic devices to realize a highly sensitive and selective microbial biosensor operating in the terahertz frequency. We optimize the various THz biosensors by changing their parameters through Finite Difference Time Domain (FDTD) simulation and fabricate the optimized biosensor by using our various fabrication facilities. With optimized THz biosensor, we are trying to detect various biological substances such as fungi, bacteria, virus, protein, DNA and et cetera.

SEM image of Terahertz Biosensor Schematic Description of Sensing Mechanism

Related Article:

  • Detection of microorganisms using terahertz metamaterials
    Scientific Reports 4, 4988 (2014); DOI: 10.1038/srep04988
    S. J. Park, J. T. Hong, S. J. Choi, H. S. Kim, W. K. Park, S. T. Han, J. Y. Park, S. Lee, D. S. Kim, Y. H. Ahn
  • Sensing viruses using terahertz nano-gap metamaterials
    Biomedical Optics Express 8, 3551 (2017); DOI: 10.1364/BOE.8.003551
    S. J. Park, S. H. Cha, G. A. Shin, Y. H. Ahn

  • Dielectric constant measurements of thin films and liquids using terahertz metamaterials
    RSC Adv. 6, 69381 (2016); DOI: 10.1039/c6ra11777e
    S. J. Park, S. A. N. Yoon, Y. H. Ahn

  • Terahertz metamaterial sensing on polystyrene microbeads: shape dependence
    Opt. Mater. Express 5, 2150 (2015); DOI: 10.1364/OME.5.002150
    S. J. Park, S. W. Jun, A. R. Kim, Y. H. Ahn

  • Sensitive detection of yeast using terahertz slot antennas
    Opt. Express 22, 30467 (2014); DOI: 10.1364/OE.22.030467
    S. J. Park, B. H. Son, S. J. Choi, H. S. Kim, Y. H. Ahn

  • Suspended single-walled carbon nanotube fluidic sensors
    Nanoscale 7, 15421 (2015); DOI: 10.1039/C5NR03215F
    B. H. Son, J. Y. Park, S. Lee, Y. H. Ahn

  

Terahertz Metamaterials and Plasmonics Using Low-Dimensional Materials

We use the highly conductive nanomaterial films (such as carbon nanotube, graphene, silver nanowire) as a novel platform for THz optical devices such as polarizers, metamaterials, and plasmonic devices.
 

Related Article:

  • Terahertz slot antenna devices fabricated on silver nanowire network films
    Opt. Mater. Express 7, 1679 (2017); DOI: 10.1364/OME.7.001679
    J. T. Hong, S. J. Park, J-. Y. Park, S. Lee, Y. H. Ahn

  • UV-induced terahertz wave modulation in freestanding ZnO nanowire films
    Opt. Mater. Express 6, 3751 (2016); DOI: 10.1364/OME.6.003751
    J. T. Hong, J. Y. Park, S. Lee, Y. H. Ahn

  • Dielectric Constant Engineering of Single-Walled Carbon Nanotube Films for Metamaterials and Plasmonic Devices
    J. Phys. Chem. Lett. 4, 3950 (2013); DOI: 10.1021/jz4020053
    J. T. Hong, D. J. Park, J. H. Yim, J. K. Park, J. Y. Park, S. Lee, Y. H. Ahn

  • Terahertz conductivity of reduced graphene oxide films
    Opt. Express 21, 7633 (2013); DOI: 10.1364/OE.21.007633
    J. T. Hong, K. M. Lee, B. H. Son, S. J. Park, D. J. Park, J. Y. Park, S. Lee, and Y. H. Ahn

  • Terahertz Wave Applications of Single-Walled Carbon Nanotube Films with High Shielding Effectiveness
    Appl. Phys. Express 5, 015102 (2012)
    J. T. Hong, D. J. Park, J. Y. Moon, S. B. Choi, J. K. Park, F. Rotermund, J. Y. Park, S. Lee, Y. H. Ahn