Download gamma radiation effects on electro

GAMMA RADIATION EFFECTS ON ELECTRO-PHYSICAL FEATURES OF
SEMICONDUCTOR MATERIALS
Rashit Maliqi, Gani Pllana
Faculty of Electrical and computer Engineering, University of Prishtina
Bregu i Diellit, p.n.10000 Prishtina, Republic of Kosova
Telephone +381 (0)38 554 896 ext.224
Abstract: A research of the influence of gamma radiation on the electrical, physical, optical, etc. features of semiconductor materials has
been made with concrete measurements conducted in the Mono-crystal of the p-type of Cadmium antimony. The influence of external factors
has been examined: like the temperature and Gamma radiation in the movement of the carriers of electric charges in semiconductor. After the
experimental measurements evidence has been concluded and presented, proving the change of these parameters. These facts are a good
basic to calculate the Hall-mobility of holes and to identify possible defects that may occur during such treatments in the semiconductor.
Key words: Chrystal, radiation, temperature, defects.
1. Introduction
3
𝑁𝑁(𝐸𝐸) = 2𝜋𝜋(2𝑚𝑚𝑒𝑒∗ )−2 (𝐸𝐸 − 𝐸𝐸𝑐𝑐 )1/2
The measurement of electrical parameters such as:
specific electrical resistance, Hall's Constanta, electric mobility
of electrical charges, magnetic susceptibility, coefficient of electrolocomotive force, etc. allow to get acquainted with the new physical
features of materials dealing with the presence of defects in
semiconductor materials. The
defects
in
the
crystal grid
significantly affect many features of the semiconductors, especially
on the electrical and optical features.
Crystals with beam radiation such
as gamma rays, fast
neutrons, laser rays, then the method of heating and cooling
after radiation are of particular interest in the study of defects in
semiconductor, because the appearance and disappearance of
defects has a major
influence on
the
physical features of
semiconductors.
A semiconductor material
that shows some
special
features during radiation, during heating and cooling is the
antimony cadmium system, for which we can find many
publications recently, due to its application as a temperature sensor.
The cadmium antimony system creates three compounds: 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶,
Some features of this composition
during
𝐶𝐶𝑑𝑑3 𝑆𝑆𝑏𝑏2 , 𝐶𝐶𝑑𝑑4 𝑆𝑆𝑏𝑏3 .
radiation are examined in the 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 semiconductor
The concentration of holes is given with:
where
𝑓𝑓ℎ - is
1
𝐸𝐸−𝐸𝐸𝐹𝐹
𝑒𝑒 𝑘𝑘𝑘𝑘
(4)
carriers of electric
𝑁𝑁(𝐸𝐸) = 2𝜋𝜋(2𝑚𝑚ℎ∗ )−3/2 (𝐸𝐸𝑣𝑣 − 𝐸𝐸𝑐𝑐 )1/2
𝑅𝑅𝐻𝐻 =
(5)
𝐸𝐸𝑓𝑓 −𝐸𝐸𝑐𝑐
𝑘𝑘𝑘𝑘
𝑎𝑎𝑎𝑎𝑎𝑎
𝑝𝑝 = 𝑁𝑁𝑣𝑣 𝑒𝑒
𝐸𝐸𝑣𝑣 −𝐸𝐸𝑓𝑓
𝑘𝑘𝑘𝑘
(6)
𝐴𝐴
(𝑝𝑝−𝑛𝑛𝑛𝑛 )2
2
𝑒𝑒 (𝑝𝑝+𝑛𝑛𝑏𝑏 )
(7)
For 𝑛𝑛 = 0, when in the semiconductor dominate the holes in the
electric conductivity, so we have:
where:
𝑅𝑅𝐻𝐻 =
𝐴𝐴
𝑒𝑒𝑒𝑒
(8)
𝐴𝐴 −is the coefficient, whose value is determined by the mechanism
of distribution of the holes in the the crystal grid, 𝑒𝑒 = 1,6 ∙
10−19 C, while p- is the concentration of the holes.
(1)
𝑓𝑓(𝐸𝐸𝐹𝐹 ) − represents the Fermi distribution function for electrons
which is given with:
𝑓𝑓𝑒𝑒 =
𝑓𝑓ℎ (𝐸𝐸, 𝑇𝑇)𝑁𝑁(𝐸𝐸)𝑑𝑑𝑑𝑑
The concentration of the bearers of the electrical charges
in the semiconductor material can also be found with a simpler
connection between the macroscopic sizes: Hall’s coefficient, the
specific electrical resistance. Hall’s coefficient is given with the
expression:
The concentration of the electrons or free holes in the
semiconductor is in the function of temperature or of the Fermi
level. Their concentration in the zone of conductivity is given with
the expression:
where
𝐸𝐸𝑣𝑣
𝑛𝑛 = 𝑁𝑁𝑐𝑐 𝑒𝑒
2. The dependence of electrical charges from
temperature
𝐸𝐸𝑐𝑐
𝐸𝐸𝐸𝐸′
If we substitute the equation for the Fermi distribution
function and the density of state in equation (1), then we obtain the
expressions for the concentration of electrons and holes in
semiconductor:
and has 16 atoms in the elementary cells [1]. In the paper [2] it is
shown that the Mono-crystal cadmium antimony has electrical
anisotropic features. The mobility of electric charges in different
crystallographic
directions has various
orientations
and the
activation energy for different crystallographic axes is in the
interval 0,56 𝑒𝑒𝑒𝑒 − 0,57 𝑒𝑒𝑒𝑒.
𝐸𝐸𝑐𝑐′
𝑝𝑝(𝑇𝑇) = 2 �
the distribution function of holes as
charges, while the density of holes is:
The 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 crystal has an orthorhombic crystal grid with the
dimensions: 𝑎𝑎 = 0,647 𝑛𝑛𝑛𝑛,
𝑏𝑏 = 0,825 𝑛𝑛𝑛𝑛, 𝑐𝑐 = 0,853 𝑛𝑛𝑛𝑛
𝑛𝑛(𝑇𝑇) = 2 � 𝐹𝐹(𝐸𝐸𝐹𝐹 )𝑁𝑁(𝐸𝐸)𝑑𝑑(𝐸𝐸)
(3)
The reciprocal value of the specific electric resistance is the specific
electrical conductivity given with:
(2)
𝑁𝑁(𝐸𝐸) − represents the density of state which in this case for the
electrons is:
where:
𝜎𝜎 = 𝑒𝑒𝑒𝑒𝜇𝜇𝐻𝐻
(9)
𝜇𝜇𝐻𝐻 - is the mobility of the holes in the semiconductor.
19
Knowing the specific values of the electrical conductivity
and Hall’s Constanta we can find the mobility of the electric
charges, e.g. of the holes:
𝜇𝜇𝐻𝐻 = 𝑅𝑅𝐻𝐻 ∙ 𝜎𝜎
3. Experimental measurements
The curve (1) in fig.1 shows the logarithmic dependence
of the specific electric resistance on temperature before the
radiation of the crystal, whereas curve (2) after radiation of the
crystal with gamma rays. Measurements were repeated for several
samples and for various dosages of radiation.
(10)
4. Discussion about the results
The curves show that gamma rays affect on the electrical
features of the semiconductor crystal because Hall’s Constanta
decreases while the concentration of the holes increases.
Experimental measurements are made in the semiconductor material of cadmium antimony, a suitable material for
changing the properties of the electrical parameters by changing the
temperature and the action of external radiation. The preparation of
the samples is made for measuring electrical parameters: the
specific
electric
resistance, Hall coefficient. About
the
nomenclature of the parameters of this material is shown in the
paper [5]. Before the radiation of the crystal samples with gamma
rays, measurements of electrical parameters were made depending
on temperature.
As a result of the interaction of gamma rays or fast
nuclear particles in the crystal grid, various types of defects occur.
With the penetration of gamma rays in the structure of the crystal
grid they provide all or part of the crystal energy. This energy that is
given to the crystal occurs as a kinetic energy in the electron. In this
case, the atoms release their own places in the crystal grid and place
themselves between the spaces of the grid.
The radiation of mono-crystal is done from the source of
gamma rays of cobalt. The source intensity was𝐼𝐼 = 3,56 ∙
105 𝑟𝑟/ℎ which gives 1,14 ∙ 1013 gamma photons per hour for
1 𝑐𝑐𝑐𝑐2 , respectively from 5,5 ∙ 1016 − 2,4 ∙ 1016 𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔/
(𝑐𝑐𝑐𝑐2 ∙ 𝑠𝑠). After the radiation of the samples the measurement
of the
specific
electric
resistance and Hall's Constanta,
depending on temperature, has been made again. The measurement
results are shown in fig. 1 and fig. 2.
In the literature [4] it is known that with the action of
gamma rays in the crystal of cadmium antimony defects appear
as with Franklin (vacancies and inter-space atoms) as a result of
elastic collisions of electrons with atoms of the grid.
Different
types
of radiation in cadmium antimony:
neutrons, protons, electrons, gamma quanta, laser rays, etc.,
show various defects where they form energetic levels in the
zone of detention. It is known that the defects of the crystal grid in
the semiconductor material, appearing by gamma radiation
[6] create recombination centers in the detention area and thus
change the electro-physical features of materials.
In the irradiated samples after
heating, experimental
measurements of Hall’s Constanta were made from the temperature
of 450 K up to room temperature, while in some samples we made
measurements at the temperature of 373 K. For all measurements
the duration was 20 minutes. During this we recorded the changes
of Hall’s Constanta, which is shown in the diagram of fig.2.
Experimental measurements show that after the action
with gamma rays and upon heating to higher temperatures appears
an instability of the defects set by radiation. Tests, done in this
case, show that when the CdSb crystal is heated to temperatures
higher than 540 K in the samples irradiated with gamma rays,
except for defects arising from radiation, thermal defects are placed
as well. In this case the super-ponation of two different defects is
done. At a large number of such semiconductors, like GE, SI,
etc., these defects are considered well and
there
is sufficient
information. However, for the CdSb semiconductor there is
little information until now that is published on the effects
of radiation on this material.
Fig.1.Dependence of specific electrical resistance on temperature
Experimental results, obtained with the case of the
gamma radiation, show that a translation of the curves of the
specific electric resistance has been done. From the
measurements that have been performed in the temperature
interval of 80 K-293K, it is clearly indicated that the gamma
radiation show a shallow acceptor level. In order to identify and to
provide details, measurements should be done at temperatures lower
than 80K.
5. CONCLUSION
Cadmium, antimony, a material with semiconductor
features, reacts during its radiation with gamma rays. It is concluded
that the gamma radiation show defects in the structure of this
crystal. Also, experimental measurements indicate that the gamma
radiation puts a shallow acceptor level in the detention area. To
do deeper analysis and to detect this level there should be done
measurements at temperatures lower than 80 K.
Fig.2 Changes of Hall’s Constanta
20
References
[1] A.E.Vol, I.K.Kagan: “Stroienie i svojstva dvoinih sistem”, Tom
IV, Nauka, Moskva,1979.
[2] Philips, C.J.: “Solid State Physics”,18, 55 ,1996.
[3] R.Hultgren,etc.: ”Selected values of the thermodynamic
properties of binary alloys”, ASM-New York, 1973
[4] G.V.Pljacko, etc, “Efektet e rrezatimit laserik në Cd Sb” ,
Ukrainski Fiziceski Zhurnal, nr. 4, p.552, 1980.
[5] Maliqi, R. etc. “The influence of the higher temperatures on the
electrical conductivity of CdSb”,ETAN 84, 1984, Split, Kroaci.
[6] Maliqi, R.; Pllana, G.:”Determination of composition and
nature of crystal thin surface layers using X-Ray radiographic
method”. Proceedings of the 22-nd International DAAAM
Symposium “Intelligent Manufacturing & Automation:Power of
knowledge and creativity” p. 1609-1610, 23-26th November 2011,
Vienna, Austria.
[7] I.V. Melnicuk, etc.: “Rasejanje rendgenski lucei monokristala
CdSb”, UFZH, n.3, p.368, 1982.
[8] B.M. Bulah etc. “Physics and technics of semiconductors”,
vol.15, N.2. Kiev,1981.
21