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Semiconductor detector as ionising radiation dosimeter
Rodmr.
Phjs.
Chem.
Vol.
Elsevier
Pergamon
46, No.
Science
4-6,
Ltd.
pp.
Printed
1287-1290, in Great
1995 Britain
0969-806X(95)00371-1
SEMICONDUCTOR
DETECTOR AS IONISING DOSIMETER
M.S.YUNUSOV,
Institute
of Nuclear
A.AKHMADALlEV,
Physics Tashkent,
RADIATION
K.A.BEGMATOV
of Academy of Sciences 702132, UZBEKISTAN
of Uzbeklstan
ABSTRACT There are presented the results of processing of y-irradiation power detector, which possesses high stabilitiy of working parameters. The possibility of its application as a radiation intensimeter and as an absorbed dose dosimeter simultaneously is also discussed. It has been showen that the obtained high stability of parameters of p-Sielr> (the concentration and the life-time of carriers) influenced by doping with Ir allows to use the detectors as a dosimeter of high absorbed doses of ionizing radiation. The ways of rising of the lower limit of dosimeters sensibility to biological absorbed dose are discussed as well. The concrete solution of this problem is suggested.
KEYWORDS Ionizing radiation; dosimeter; iridium doped silicon. In most p - i - n detectors i - region is created by compensation of the material with low initial resistivity (p) [1,2,3]. For this purpose the compensation of Si is realized usually by fast diffusive impurity doping. The successful doping impurity choice allows to obtain the detector parameters stable against irradiation induced degradation so that a higher power radiation dose can be measured. From this point of view the application of Ir as a doping impurity was proved to be very successful for some reasons. The first, Ir-impurity in Si has very fast diffusion rate (Dz 2.10-7+2.10-6cm2.s-1). It permits to realize the short time thermodiffusion compensation of n - and p - Si with a large depth and a wide scale of initial values of p. The second, Ir in n - Si was found to show strong recombinational properties, so that the life time of current carriers 7, decreases up to - 10mgs [4,5,6]. The last is very important for fast operating devices contruction. As to Ir in psi the situation is quite peculiar recombination properties are not realized practically, therefore a value of 7 increases as compared to that of the initial psi (Fig.1.). We have established that life time of carriers increased until 500 t 700 ~LSwith initial holes concentration increasing at realization of conductivity full compensation conditions by Ir. The third, the compensation of Si with Ir has been found to lead to high stability of the most important parameters of semiconductor (for instance, concentration and the life-time of carriers) against the irradiation induced degradation [6]. Fig.2).
1288 M. S. Yunusov
ef al.
o~--l--p-~--i~~B Nh
1 O’6cm-s
Fig. 1. Dependence of the 7 in p - Si on concentration of Ir (the initial concentration of holes p~3.10’ 5 cmm3).
The electronic states spectrum for p - Siclr> was investigated by DLTS-method and two Ir local levels were found in the lower part of gap: E,=E,+0.30 eV and E2=Ev+0.57 eV. The charge trap cross-sections and the centers concentration are correspondingly 01=2.7.1 O13cm2, Nl=9.8.1013cm-3 and a2=7.7.10’15cm2,N2=1.2.1014 cm3. Naturally there are some interesting physical mechanisms of Ir influence on he above mentioned Si properties. However we don’t discuss them at the present stage of our investigation (it will be publisled later). It is possible Ir doping of p - Si creates the centers some of which are levels of sticking for holes and leads to increase in their life-time. As mentioned above, Ir can compensate a conductivity of the Si practically till the self value [71 Besides, the life time increase resulting from the compensation depends on a dopant concentration (Fig.1 .). Furthermore after doping the parameters of material (specific resistivity, life time of current carriers) possess a higher radiation stability (Fig.2). So, one can be see that p-Si+z= is a good material for constructing the dosimeter of large ionization radiation fluences. Based on this idea p-i-n-structures have been constructed on the base of psi, compensated by Ir. The initial material was psi with different resistivities. Doping of Si with Ir was performed by the thermodiffusional method. A time and a temperature of the diffusion process are dependent on a depth of the compensated layer, which was up to 300 pm in these experiments. The means of dose power registration of ionizing radiation is based on measurement of short currents (1s.~) in photovoltaic regime of operation. In this case the electromotive force appears due to radiation induced generation of electron-hole pairs in a base layer and their separation by means of field of transition. In photovoltaic regime produced detector has demonstrated the linear dependence of Iglsc. on power of irradiation in the range of 100+600 R/s (Fig.3). The current sensitivity (q) is n=(2s3).10”
A/@/s).
9th International
Meeting
on Radiation
Processing
D, 10’
Fig. 2. Dependence
Fig. 3. Dependence
1289
Gy
of the T (1) and p (2) on a total dose.
of 1gls.c. on of a dose power.
Investigation of the n stability under 6o Co y-irradiation has shown that q decreases by less than 15% at dose - 2.107Gy. It is well seen that linearity of 1s.~. on a dose rate is constant, up to an irradiation dose of pure Si-detectors-106Gy. Temperature variation of rt in an interval of 20 t 60 OC is not more than OJ%/OC. For increasing of the detector sensitivity to a biological absorbed dose, the electronic scheme was elaborated to integrate detector pulses followed by registration with the standard digital device (type of PSD-2M). This equipment permits to widen the interval of dose measurement: a lower limit - IO-*Gy; an upper limit 1O’Gy.
1290
M.
S. Yunusov
et al
REFERENCES
[l]
G.Dearnally, 1964.
D.C. Northorp.
Semiconductor
[I?!] Akinov Yu.K. at all. Semiconductor Moscow, Energoatomizdat, 1989.
counters
detector
for nuclear radiations,
in experimental
physics
London,
(in Russian),
[3]
Fedoseeva L.C. at all. The silicon detectors Moscow, Energoatomizdat, 1983.
of the ionizing raditaion (in Russian),
[4J
Yunusov M.S., Akhmadaliev A., Turaev T.N. Electrophysical and recombination properties of the silicon, doped by iridium (in Russian) Uzbekian Physical Journal, 1994, n2, p.24.
[5]
Liziak K.P. and Milnes A.G., Rhodium Electron. 1976, vol.1 9, p,p.11!5-119.
[6]
Physical properties of irradiated Fan, 1987, p,p. 117-l 19.
[7]
Yunusov Russian),
and Iridium as deep impurities
silicon
(in Russian),
editor:
in silicon. Sol. St.
Yunusov
M.&Tashkent,
M.S., Physical properties of the silicon doped with platinium group of metals (in Tashkent, Fan, 1983, p.80.
Phjs.
Chem.
Vol.
Elsevier
Pergamon
46, No.
Science
4-6,
Ltd.
pp.
Printed
1287-1290, in Great
1995 Britain
0969-806X(95)00371-1
SEMICONDUCTOR
DETECTOR AS IONISING DOSIMETER
M.S.YUNUSOV,
Institute
of Nuclear
A.AKHMADALlEV,
Physics Tashkent,
RADIATION
K.A.BEGMATOV
of Academy of Sciences 702132, UZBEKISTAN
of Uzbeklstan
ABSTRACT There are presented the results of processing of y-irradiation power detector, which possesses high stabilitiy of working parameters. The possibility of its application as a radiation intensimeter and as an absorbed dose dosimeter simultaneously is also discussed. It has been showen that the obtained high stability of parameters of p-Sielr> (the concentration and the life-time of carriers) influenced by doping with Ir allows to use the detectors as a dosimeter of high absorbed doses of ionizing radiation. The ways of rising of the lower limit of dosimeters sensibility to biological absorbed dose are discussed as well. The concrete solution of this problem is suggested.
KEYWORDS Ionizing radiation; dosimeter; iridium doped silicon. In most p - i - n detectors i - region is created by compensation of the material with low initial resistivity (p) [1,2,3]. For this purpose the compensation of Si is realized usually by fast diffusive impurity doping. The successful doping impurity choice allows to obtain the detector parameters stable against irradiation induced degradation so that a higher power radiation dose can be measured. From this point of view the application of Ir as a doping impurity was proved to be very successful for some reasons. The first, Ir-impurity in Si has very fast diffusion rate (Dz 2.10-7+2.10-6cm2.s-1). It permits to realize the short time thermodiffusion compensation of n - and p - Si with a large depth and a wide scale of initial values of p. The second, Ir in n - Si was found to show strong recombinational properties, so that the life time of current carriers 7, decreases up to - 10mgs [4,5,6]. The last is very important for fast operating devices contruction. As to Ir in psi the situation is quite peculiar recombination properties are not realized practically, therefore a value of 7 increases as compared to that of the initial psi (Fig.1.). We have established that life time of carriers increased until 500 t 700 ~LSwith initial holes concentration increasing at realization of conductivity full compensation conditions by Ir. The third, the compensation of Si with Ir has been found to lead to high stability of the most important parameters of semiconductor (for instance, concentration and the life-time of carriers) against the irradiation induced degradation [6]. Fig.2).
1288 M. S. Yunusov
ef al.
o~--l--p-~--i~~B Nh
1 O’6cm-s
Fig. 1. Dependence of the 7 in p - Si
The electronic states spectrum for p - Siclr> was investigated by DLTS-method and two Ir local levels were found in the lower part of gap: E,=E,+0.30 eV and E2=Ev+0.57 eV. The charge trap cross-sections and the centers concentration are correspondingly 01=2.7.1 O13cm2, Nl=9.8.1013cm-3 and a2=7.7.10’15cm2,N2=1.2.1014 cm3. Naturally there are some interesting physical mechanisms of Ir influence on he above mentioned Si properties. However we don’t discuss them at the present stage of our investigation (it will be publisled later). It is possible Ir doping of p - Si creates the centers some of which are levels of sticking for holes and leads to increase in their life-time. As mentioned above, Ir can compensate a conductivity of the Si practically till the self value [71 Besides, the life time increase resulting from the compensation depends on a dopant concentration (Fig.1 .). Furthermore after doping the parameters of material (specific resistivity, life time of current carriers) possess a higher radiation stability (Fig.2). So, one can be see that p-Si+z= is a good material for constructing the dosimeter of large ionization radiation fluences. Based on this idea p-i-n-structures have been constructed on the base of psi, compensated by Ir. The initial material was psi with different resistivities. Doping of Si with Ir was performed by the thermodiffusional method. A time and a temperature of the diffusion process are dependent on a depth of the compensated layer, which was up to 300 pm in these experiments. The means of dose power registration of ionizing radiation is based on measurement of short currents (1s.~) in photovoltaic regime of operation. In this case the electromotive force appears due to radiation induced generation of electron-hole pairs in a base layer and their separation by means of field of transition. In photovoltaic regime produced detector has demonstrated the linear dependence of Iglsc. on power of irradiation in the range of 100+600 R/s (Fig.3). The current sensitivity (q) is n=(2s3).10”
A/@/s).
9th International
Meeting
on Radiation
Processing
D, 10’
Fig. 2. Dependence
Fig. 3. Dependence
1289
Gy
of the T (1) and p (2) on a total dose.
of 1gls.c. on of a dose power.
Investigation of the n stability under 6o Co y-irradiation has shown that q decreases by less than 15% at dose - 2.107Gy. It is well seen that linearity of 1s.~. on a dose rate is constant, up to an irradiation dose of pure Si-detectors-106Gy. Temperature variation of rt in an interval of 20 t 60 OC is not more than OJ%/OC. For increasing of the detector sensitivity to a biological absorbed dose, the electronic scheme was elaborated to integrate detector pulses followed by registration with the standard digital device (type of PSD-2M). This equipment permits to widen the interval of dose measurement: a lower limit - IO-*Gy; an upper limit 1O’Gy.
1290
M.
S. Yunusov
et al
REFERENCES
[l]
G.Dearnally, 1964.
D.C. Northorp.
Semiconductor
[I?!] Akinov Yu.K. at all. Semiconductor Moscow, Energoatomizdat, 1989.
counters
detector
for nuclear radiations,
in experimental
physics
London,
(in Russian),
[3]
Fedoseeva L.C. at all. The silicon detectors Moscow, Energoatomizdat, 1983.
of the ionizing raditaion (in Russian),
[4J
Yunusov M.S., Akhmadaliev A., Turaev T.N. Electrophysical and recombination properties of the silicon, doped by iridium (in Russian) Uzbekian Physical Journal, 1994, n2, p.24.
[5]
Liziak K.P. and Milnes A.G., Rhodium Electron. 1976, vol.1 9, p,p.11!5-119.
[6]
Physical properties of irradiated Fan, 1987, p,p. 117-l 19.
[7]
Yunusov Russian),
and Iridium as deep impurities
silicon
(in Russian),
editor:
in silicon. Sol. St.
Yunusov
M.&Tashkent,
M.S., Physical properties of the silicon doped with platinium group of metals (in Tashkent, Fan, 1983, p.80.