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Modulation transfer function characteristic of uniform-doping transmission-mode GaAs/GaAlAs photocathode |
Ren Ling(任玲)† and Chang Ben-Kang(常本康) |
Institute of Electronic Engineering and Optoelectronic Technology, Nanjing University of Science and Technology, Nanjing 210094, China |
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Abstract The resolution characteristic can be obtained by the modulation transfer function (MTF) of a GaAs/GaAlAs photocathode. After establishing the theoretical model of GaAs(100)-oriented atomic configuration and the formula for the ionized impurity scattering of the non-equilibrium carriers, this paper calculates the trajectories of photoelectrons in a photocathode. Thus the distribution of photoelectron spots on the emit-face is obtained, which is namely the point spread function. The MTF is obtained by Fourier transfer of the line spread function obtained from the point spread function. The MTF obtained from these calculations is shown to depend heavily on the electron diffusion length, and enhanced considerably by decreasing the electron diffusion length and increasing the doping concentration. Furthermore, the resolution is enhanced considerably by increasing the active-layer thickness, especially at high spatial frequencies. The best spatial resolution is 860 lp/mm, for the GaAs photocathode of doping concentration 1 × 1019 cm-3, electron diffusion length 3.6 μm and the active-layer thickness 2 μm, under the 633-nm light irradiated. This research will contribute to the future improvement of the cathode's resolution for preparing a high performance GaAs photocathode, and improve the resolution of a low light level image intensifier.
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Received: 24 November 2010
Revised: 01 March 2011
Accepted manuscript online:
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PACS:
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73.61.Ey
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(III-V semiconductors)
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42.30.Lr
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(Modulation and optical transfer functions)
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73.50.-h
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(Electronic transport phenomena in thin films)
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79.60.-i
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(Photoemission and photoelectron spectra)
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Fund: Project supported by the National Natural Science Foundation of China (Grant No. 60678043) and the Research and Innovation
Plan for Graduate Students of Jiangsu Higher Education Institutions, China (Grant No. CX09B 096Z). |
Cite this article:
Ren Ling(任玲) and Chang Ben-Kang(常本康) Modulation transfer function characteristic of uniform-doping transmission-mode GaAs/GaAlAs photocathode 2011 Chin. Phys. B 20 087308
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