中国物理B ›› 2011, Vol. 20 ›› Issue (8): 87308-087308.doi: 10.1088/1674-1056/20/8/087308

• CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES • 上一篇    下一篇

Modulation transfer function characteristic of uniform-doping transmission-mode GaAs/GaAlAs photocathode

任玲, 常本康   

  1. Institute of Electronic Engineering and Optoelectronic Technology, Nanjing University of Science and Technology, Nanjing 210094, China
  • 收稿日期:2010-11-24 修回日期:2011-03-01 出版日期:2011-08-15 发布日期:2011-08-15
  • 基金资助:
    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).

Modulation transfer function characteristic of uniform-doping transmission-mode GaAs/GaAlAs photocathode

Ren Ling(任玲)† and Chang Ben-Kang(常本康)   

  1. Institute of Electronic Engineering and Optoelectronic Technology, Nanjing University of Science and Technology, Nanjing 210094, China
  • Received:2010-11-24 Revised:2011-03-01 Online:2011-08-15 Published:2011-08-15
  • Supported by:
    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).

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摘要： 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.

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.

Key words: GaAs/GaAlAs photocathode, uniform-doping, modulation transfer function, spatial resolution

中图分类号:  (III-V semiconductors)

  • 73.61.Ey
42.30.Lr (Modulation and optical transfer functions) 73.50.-h (Electronic transport phenomena in thin films) 79.60.-i (Photoemission and photoelectron spectra)