Effects of 10 MeV Proton Irradiation
on Electrical Properties of GaAs
M. Kitagawa and K. Morimoto
Radiation Center of Osaka Prefecture, 704 Shinke-cho, Sakai, Osaka
S. Yoshida, K. Mitsui, and Y. Yukimoto
LSI Research and Development Laboratory, Mitsubishi Electric Corporation
4-1 Mizuhara, Itami, Hyogo
Introduction
Radiation effects on GaAs crystals are lesswellunderstood than on Si andGe. Solid state devices are sometimes employed in the field of ionization
radiation. Recent progress in the development of GaAs devices requires further study of radiation effects on this material. The impurity conduction
process in GaAs is an important subject to be studied as well as the usual
conduction band conduction process because of the difficulty of material
purification at present and then high impurity concentration in device material put to practical use.
This paper is concerned with proton irradiation effects on electrical properties of n-type GaAs single crystals. It has been investigated that the proton
induced defects acting as acceptors play an important role in conduction
process and an activation energy £3 of the hopping conduction process varies
with changing impurity compensation.
Experimental Results and Discussion
Hall effect measurement were made with a conventional de method at temperatures between 10 and 300 K for three samples T21-02, Gll-03, and G3n-Ol
having different concentrations n=l.6xl018, 1.3xl017, and 2.6xl016 cm-3 at
300 K, respectively. Before irradiation the temperature dependence of theelectrical properties indicates that the conduction due to the' impurity conEspecially the sample
duction process is significant in all the samples.
with the highest carrier concentration (T21-02) shows almost completely constant resistivity in the whole temperature range, namely, the metallic impurity
conduction occurs. The hopping type conduction with an activation energy t3
Irradiation wasis observed at low temperature region in the sample G3n-Ol.
carried out at room temperature by 10 MeV protons from a cyclotron of The
Institute of Physical and Chemical Research.
With irradiation the carrier concentration n and the carrier mobility p
decreased, and then the electric resistivity p increased. The carrier removal
rate, -dn/d~, was much larger than that of high energy electron irradiation.l)
The decrease in carrier concentration suggests the increase in number ofacceptor-type defects. The change in n with irradiation is listed in Table 1.
Carrier concentration of p-type GaAs also decreased by 10 MeV proton irradiation,2) which suggests that donor-type defects are also produced. The facts
indicate the creation of both the donor-type and acceptor-type defects byproton irradiation. Different type defects are active in different type (nor p) samples. This is due to the position of the Fermi level in the forbidIn high conductive n-type samples the Fermi level is close toden band.
the bottom of the conduction band and all acceptor-type defects except thedefects whose energy levels lie above the Fermi level are active and capture
the conduction electrons, while most donor-type defects except very shallow
donors are inactive.
Magnitude of the carrier mobility gives valuable information on the conIt is clear that the change in mobility atcentration of charged centers.
300 K is resulted from a change in concentration of charged scattering centers
by irradiation. From the analysis of the mobility data charged donor concentration Nd+and acceptor concentration Na- were calculated.3) It became evident
from the calculation that the decrease in n with irradiation was due to alarger increase in acceptor concentration than an increase in acting donor
concentration.
-163-Table 1.

Change in n (cm-3) at 300 K with irradiatio n~ence (protons/ em 2)Samp
0T21-02

1. 5x10l3

1.61x1018

Gll-03G3n-015x10122.58x1016

4.5x10l3
1.46x1018

1. 28x1017

1.12x1017

2.07x1o16

1.67x1016

1.29x1017

Figure 1 shows the temper10°~-------------------------------.
ature dependenc e curvesof electric resistivi ty p
1.5E13
before and after irradiation for each sample.
5E12/
The resistivi ty of all thebefore//"'
samples increased in wno1eII.. -··
temperatu re range with ir.i
10-1
radiation .
/..··.-··In the sample_/ ,/G3n-01G3n-01 two activatio nE
processes of impurity()
conductio n were observed:-·-·-·-·-·-·- ·-·-·- 4.5E 13
E/ 1.5E13
the hopping conductio n.r::.... ----····
0with an activatio n energy-.. 5E12'-'.-··
C3 and another type of
G11-03>impurity conductio n with>£2 which appears charac.....(/)
teristica lly in the inter(/)
mediate impurity concentQ)
ration samples. £ 3 increas0:
4.5E13
T21-02
ed slightly with irradi/
ation.
It is deduced"-before
that the increase in p
10-3of G3n-01 and G11-03 arises
from a decrease in donorsite electrons because of
the increase in compensa tion.
When the compensa tion
increases , the random
10-4L-_L__J __ _L _ _ L_ _J __ _L-~~~--~-7
potential becomes greater
0 .1 .2 .3 .4 .5 .6 .7 .8
and the mobility edge may
9 1.0
be shifted upwards and then
10/T
increases .4l
Theincrease in p of T21-02 possibly reflects a decrease in number of electrons
in the impurity band.

--t3

Reference s1), 2) M.Kitagaw a and K.Morimot o, unpublish ed.
3) K.Morimot o, M.Kitagaw a, and T.Yoshida , J.Cryst.G rowth 59, 257(1982).
4) N.F.Mott and E.A.Davis , "Electron Processes in Non-Crys talline Materials"
Clarendon Press Oxford, 1979.

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