Comparative research on indium seal process for transmission-mode
GaAs photocathodes
Liang Chen
a,
n
, Shuqin Zhang
a
, Shangzhong Jin
a
, Sunan Xu
a
, Gangcheng Jiao
b
a
Institute of Optoelectronics Technology, China Jiliang University, 310018 Hangzhou, China
b
Science and Technology on Low-Light-Level Night Vision Laboratory, 710065 Xi'an, China
article info
Article history:
Received 22 July 2013
Received in revised form
19 August 2013
Accepted 20 August 2013
Available online 3 September 2013
Keywords:
GaAs photocathode
Surface photovoltage spectroscopy
Indium seal process
abstract
For night vision devices and other applications, the transmission-mode photocathodes must be sealed to
tube by indium seal process (ISP) in practical application. But in early researc h, the integr al sensitivity has
large drop to about 30% amplitude after ISP process than after activation process. In order to well study the
influence of ISP on surface barriers of activat ed GaAs photo cathodes, we used the comparative research
method by surface photov oltag e spectroscop y (SPS) and spectral response current (SRC ). Through fitting
calculation, we can find that the impurity gas sources by micro channel plate and fluorescent screen have
deep influence on the amplitude and width of surface barriers which lead to the large drop on SRC curves
before and after ISP process. This on-line comparative research method can help to optimize ISP technique
and vacuum degree optimization for transmission-mode GaAs photocathodes in the future.
& 2013 Published by Elsevier B.V.
1. Introduction
Negativ e electron affinity GaAs photocathode s activat ed by cesium
(Cs) and oxy ge n (O) have becom e increasingly importan t to be
efficient emitters in night vision devices and polarized electron
sources because of their high qu antum efficiency , narrow energy
spread and low dark emission. For most practical device applications,
the Cs–O activated GaAs photocathodes must operate in transmission-
mode. The performance of photocathodes mainly depends on three
factors, namely , electron diffusion length, bac k interface recombination
velocity and surface escape probability. The former two factors are
related to the body properties of the grown cathode materials, while
the later factor is related to the crystal face, the surface cleaning
procedure and the particular activ ation techniq ue [1–4]. Thus the
final performance for activated cathode material will be decided not
only by cathode material but also activation technique. So in recent
years, many resear ches have been carried out on cathode structure
and activation techniqu e [3–5,10]. But for night vision devices, the
transmission-mode phot ocathodes must be sealed to tube by ISP in
practical application. Thus the influence of ISP techniq ue for activat ed
GaAs photocathodes must be taken into account. For example, one
uniform doping transmission-mode GaAs photocathode can acquire
the value of SRC value to above 1 300 mA/lm in activating room by
Cs–O activation, while after ISP, the value of SRC can only attach to
about 800 mA/lm. So the ISP technique will deeply affect the surface
properties and the research on ISP technique will help to further
promote the propertie s of transmission-mode photocathodes in night
vision devices. But in early resear ch, the resear ch on activation
techniqu e and ISP technique mainly depend on measuring SR C curves
after these processes. For SRC values are influenced by not only
activation and seal techniq ue but also material properties, so the ISP
techniqu e has not been well studied. In recent research, we carried out
comparative research though SPS before activation and SRC after
activation on cathode structure design and activ ation technique [3–5].
For the SPS values are only in connection with cathode material
properties, thus through this comparative method, the value of surface
escape probability for photo-e xcited electrons can be well fitted.
Furthermore, by means of surface barrier model, the values of surface
barriers can also be finally well fitted by surface escape probability
curves. So this comparative research method has well effect on
material structure design and activ ation te chniq ue in recent resear ches
[8–10]. Thus in this paper , we apply this comparative research method
on ISP technique and the variations on surface barriers after ISP can be
well fitted which can also explain the drop for SRC values before and
after ISP. The research results will help to well study ISP technique for
transmission-mode GaAs photocathodes in the future.
2. Experiment
In order to carry out comparative research on ISP technique for
transmission-mode GaAs photocathodes, the designed cathode
material was grown on the high quality p-type GaAs (100)-oriented
Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/optcom
Optics Communications
0030-4018/$ - see front matter & 2013 Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.optcom.2013.08.064
n
Corresponding author.
E-mail addresses: 52571497@qq.com, sunembed@yahoo.com.cn (L. Chen).
Optics Communications 311 (2013) 385–388