Variation of spectral response for exponential-doped
transmission-mode GaAs photocathodes in the
preparation process
Yijun Zhang,
1
Jun Niu,
1,2
Jijun Zou,
1
Benkang Chang,
1,
* and Yajuan Xiong
1
1
Institute of Electronic Engineering and Optoelectronic Technology, Nanjing University of Science and Technology,
Nanjing 210094, China
2
Department of Electronic and Electric Engineering, Nanyang Institute of Technology, Nanyang 473004, China
*Corresponding author: bkchang@mail.njust.edu.cn
Received 23 March 2010; revised 27 May 2010; accepted 15 June 2010;
posted 17 June 2010 (Doc. ID 125797); published 8 July 2010
To confirm the actual effect of an exponential-doped structure on cathode performance, an exponential-
doped structure was applied to the preparation of a transmission-mode GaAs photocathode, and spectral
response curves after high-temperature activation, low-temperature activation, and the indium sealing
process were separately measured by use of the on-line spectral response measurement system. The re-
sults show that, compared to the previously uniform-doped photocathode, the exponential-doped photo-
cathode can obtain higher cathode performance and photoemission capability because of the built-in
electric field. Nevertheless, cesium desorption and impurity of gas during the sealing process can cause
the degeneration of spectral response in the entire response waveband, especially in the long-wavelength
region, with the decrease in surface electron escape probability related to the adverse evolution of the
surface potential barrier profile. © 2010 Optical Society of America
OCIS codes: 160.2100, 250.0250.
1. Introduction
Negative electron affinity (NEA) GaAs photo-
cathodes activated by cesium and oxygen have al-
ready found widespread application in night visi on
imaging intensifiers and polarized electron sources
due to their high quantum efficiency, good long-
wavelength response, and low energy spread [1–4].
For most practical device applications, the photo-
cathodes must operate in the transmission mode.
Meanwhile, the characteristics of quantum values
for transmission-mode (t-mode) GaAs photocathodes
mainly depends on three factors, namely, electron
diffusion length, back interface recombination ve-
locity, and surface electron escape probability [5].
The former two factors are related to the quality of
the grown cathode material, while the latter factor
is related to the activation technique. To improve
NEA photocathode performance, an exponential-
doped structure on reflection-mode (r-mode) GaAs
photocathodes was put forward as complying with
the bulk photoemission effect [6], which can obtain
higher quantum efficiency than the uniform-doped
one. However, there are few reports with respect
to the exponential-doped r-mode GaAs photo-
cathodes, rather than the practical t-mode GaAs
photocathodes [7,8]. In this paper, we apply this
exponential-doped structure to the preparation of
t-mode GaAs photocathodes.
In addition, although the spectral response curves
of GaAs photocathodes during the activation process,
after activation, and indium seal have been widely
investigated [9–11], little work on the variation of
the spectral response for the exponential-doped t-
mode GaAs photocathodes during the preparation
process has been published in earlier studies. Using
an on-line spectral response measurement system,
0003-6935/10/203935-06$15.00/0
© 2010 Optical Society of America
10 July 2010 / Vol. 49, No. 20 / APPLIED OPTICS 3935
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