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Sensors of high-energy radiation based on amorphous chalcogenides
A
ELSEVIER
Sensorsand ActuatorsA 68 ( 1998) 356-358
PHYSICAL
Sensorsof high-energy radiation basedon amorphouschalcogenides 0.1. Shpotyuk a7b,*,V.O. Balitska a, M.M. Vakiv a, L.I. Shpotyuk a aLviv Scientific Research Institute of Materials, Stryjska St. 202, UA-290031, Lviv, Ukraine h Physics Institute of Pedagogical University of Czestochowa, Al. Armii Krajowej 13/15, PL-42201, Czestochowa, Poland
Abstract Possibilities of practical application of amorphouschalcogenidesemiconductorsobtained in the form of bulk glassesasradiation-sensitive elementsof solid-state dosimetric systemsfor high-energy ionizing radiation are analysed. It is establishedthat the most suitable for this 0 1998Elsevier ScienceS.A. All purposeare sensorsbasedon the electrical and photoelectrical propertiesof the investigated materials. rights reserved. Keywords: Amorphous chalcogenide semiconductors; Radiation sensors; Photoconductivity
1. Introduction
Optical dosimetric systemsbasedon amorphouschalcogenide semiconductors (AChSs) can be used for radiation measurements in a wide range of absorbed doses (from 1O2 to IO7Gy) of high-energy ionizing radiation [ 11.Suchradiation sensors are characterized by a low barrier of information bleaching (440-470 K) [2] in comparison with widely used
ones based on coloured oxide glasses [ 3,4] I The physical principles of their functioning areso-calledradiation destruction-polymerization transformations accompaniedby concentration changesof coordination defects,studied in detail using the far-JRFourier spectrometrytechnique [ 5-81. The optical properties of AChSs, first of all the optical density D in the middle point of the upper part of the fundamental optical transmission edge, being tightly connected with their defectstate,dependmonotonically on theabsorbed dose @in agreementwith the expression ADID,=Slg@+A
(1)
where A is some constant for a specific AChS composition and S is the device sensitivity. However, it is well known that the electrical and photoelectrical properties of AChSs are also determined by the coordination-defect concentration [ 91. Hence we suppose
that the level of radiation influence can be estimatedarising from radiation-induced defect changesin the sameway. It mustbe noted that a similar principle of functioning is proper
to radiation sensorswith sensitiveelementsmadeof crystal* Corresponding author. Tel.: + 7-380-322-634-205; Fax: + 7-380-322632-228; E-mail: [email protected]
line semiconductors,but they have a low level of registered dosesand sensitivities [ 3,4]. We shall consider in this paper the new experimental results obtainedusing AChS samples in the form of bulk As,Se,-basedchalcogenide glassesin order to confirm this supposition. 2. Experiments
Investigated AChS samples of ( As,Se,),(Sb,Se,) I --x (0.75 2x5 1.OO) compositions were prepared from highpurity elementalconstituentsby direct synthesisin evacuated quartz ampoulesasdescribedpreviously in Refs. [ 5-81. The standardrocking furnace techniquefollowed by air quenching was applied. After synthesis all ingots were cut to 1 mm X 1 mm X 5 mm parallelepipeds.It was confirmed by Xray diffraction measurementsthat phaseseparationand crystallization are absentin the samples.Two kinds of samples were selected for experimental measurements: freshly obtained and previously thermoannealedin air (at T= 420430 K for 3 to 5 h). The dosimetric characteristicsof bulk AChS samples were studied after irradiation by y-quanta from a 6oCosource. The dark electrical conductivity u and maximal intensity of spectral photoconductivity aPhwere used as radiation-sensitive parametersin our experiments
[lOI * 3. Results
The main characteristicsof radiation-sensitive dosimetric systemsbasedon As,Se, chalcogenideglassesarepresented in Table 1.
0.1. Shpotyuk et al. /Sensors
and Actuators
357
A 68 (1998) 356-358
Table 1 Dosimetric characteristics of As,Se,-based chalcogenide glasses Radiation-sensitive element
Control parameter
Range of doses A@, Gy
Sensitivity S, au.
Freshly obtained Freshly obtained Thermoannealed Thermoannealed Freshly obtained Freshly obtained Thermoannealed
Au/a<0 Au/u<0 Ada>0 Ada>0 Au,,lu,,O
5x105-5x106 5 x los-5 x 106 7.5 x 105-10’ 5 x IO”-2 x 10’ 3x los-2x IO6 3 x lo”-2 x 106 3 x lOj-5 x lo6
0.06 0.15 1.00 0.34 0.65 0.95 0.87
A&Se3 bulk glasses (As,Se,),,,(Sb,Se,)~,~ glasses As&Se, glasses (AsaSe3)085(Sb2Se3)0 ,s glasses As,Se, bulk glasses (As,Se,), so(Sb,Se,),,,, glasses As,Se, glasses
Not all our investigated radiation-sensitive elementscan be used repeatedly becauseirreversible radiation-structural transformations were produced by chemical interaction of absorbed impurities and the destroyed units of the glassy network aretoo high for thesecompositions [ 111.Apartfrom this feature,As,Se,-basedelectrical dosimetric systemshave a relatively narrow range of registereddosesin comparison with AChS-basedoptical sensors[ 11. The dosimetric characteristicsof such sensorsare quite reproducible in the wide range of preparation conditions. Only thermal annealing has a significant influence on thesesensors. It is establishedthat freshly obtained As,Se,-basedchalcogenide glasses are characterized by negative radiationinduced changes of control parameters. The maximum sensitivity Sdoesnot exceed0.15 in the caseof dark electrical conductivity measurements,while it is approximately equal to 1.Ofor aphmeasurements.Chalcogenideglassespreviously thermoannealedat a temperature near the glass transition point have higher sensitivities for both u and oPhmeasurements.Thus AChSs obtainedby the traditional direct synthesis methodhave predictable sensitivity characteristicsbut the thermal annealing conditions must be taken into account.
4. Discussion Solid-state dosimetric systemsbasedon freshly obtained and previously thermoannealed(As,Se,),( Sb,Se,) 1--xchalcogenideglassesare characterizedby high sensitivities to yirradiation of the 6oCoradioisotope. Taking into account experimental results on the microstructural mechanismof radiation-inducedtransformationsin AChS [ 7,8], we conclude that the observedchangesof dark electrical conductivity c and the maximum value of spectral photoconductivity aPhare mainly connectedwith coordination-defect formation processes.But impurity radiationchemical interactions led to the formation of OH-, CH- and CO-containing complexes [ 111which play an important role too and explain the irreversibility of the investigatedsensors. Coordination-defect formation processesare associated with chemical-bond switching [ 7,8]. Instead of a chemical bond being destroyed,another one forms and the balanceof the new bondsis stabilized in the glassstructure.The number of covalent chemical bonds is not changedduring this proc-
ess,but the mean energy of the bond network may reach a new level different from the initial one.Moreover, two point defectsappearin the neighborhood with transformedbonds, over- and under-coordinated atoms having uncompensated negative andpositive charges.It is supposedthat the microstructural nature of coordination-defectformation in AChS is explained by exciton self-trapping [ 121 or excitation of socalled soft atomic configurations [ 131.
5. Conclusions The dosimetric characteristicsof As&-based chalcogenide glassesfor y-irradiation measurementshavebeenstudied. It has been shown that these materials can be conveniently usedasradiation-sensitive elements.The dark electrical conductivity and the maximum value of the spectralphotoconductivity are expected to be the most suitable control parametersof these sensors,characterizedby the necessary reproducibility of measurementsand high sensitivity. But irreversible effects causedby radiation-structural transformations limit the repeateduse of AChS sensors.The microstructural mechanismof suchtransformationsis basedon the coordination-defect formation processesand chemical-bond switching.
References t11 0.1. Shpotyuk,
Amorphous chalcogenide semiconductors for dosimetry of high-energy ionizing radiation, Radiat. Phys. Chem. 46 ( 1995) 1279-1282. [21 0.1. Shpotyuk, Temperature stability of gamma-induced effects in vitreous arsenic trisulphide, Zh. Prikl. Spektroskopii 46 ( 1987) 122126. [31 A.K. Pikaev, Modern Radiation Chemistry, Main States, Experimental Technique and Methods, Nauka, Moscow, 1985, p. 375. I41 M. Frank, B. Shtolz, Solid State Dosimetry of Ionizing Radiation, Atomizdat, Moscow, 1973, p. 247. [51 0.1. Shpotyuk, A.P. Kovalsky, M.M. Vakiv, O.Ya. Mrooz, Reversible radiation effects in vitreous AsaS,, Phys. Status Solidi A 144 ( 1994) 277-283. I61 0.1. Shpotyuk, A.O. Matkovskii, Radiation-stimulated processes in vitreous arsenic trisulphide, .I. Non-Cry& Solids 176 (1994) 45-50. [71 0.1. Shpotyuk, Mechanism of radiation-structural transformations in amorphous As&, Rad. Eff. Defects Solids 132 (1994) 393-396.
358
0.1. Shpotyuk et al. /Sensors and Actuators A 68 (1998) 356-358
[81 0.1. Shpotyuk,
Reversible radiation effects in vitreous A&. 2. Mechanism of structural transformations, Phys. Status Solidi A 145 ( 1994) 69-75. [91 A. Feltz, Amorphous and Vitreous Inorganic Solids, Mir, Moscow, 1986, p. 558. 1101 A. ROW, Photoconductivity Principles, Mir, Moscow, 1966, p. 192. 11110.1. Shpotyuk, Spectroscopic study of penetrating radiation influence on surface of vitreous arsenic chalcogenides, Ukr. Fiz. Zh. 32 ( 1987) 509-5 12, 1121R.A. Street, Non-radiative recombination in chalcogenide glasses, Solid State Commun. 24 (1977) 363-365. [I31 M.I. Klinger, Model of electronic processes in glassy semiconductors: correlation with structural features, Solid State Commun. 45 ( 1983) 949-953.
Biographies Oleg Shpotyukwasborn in 1958and is a Doctor of PhysicalMathematical Sciences.He graduatedfrom the Materials ScienceDepartmentof Lviv StateUniversity (Ukraine) in 1980.
He is the researchdirector of the scientific researchcompany Carat (Lviv, Ukraine). His scientific interests include materials scienceengineering and defect-formation processesin disorderedsolids. Valentina Balitska wasborn in 1954.Shegraduatedfrom the SemiconductorPhysicsDepartmentof Lviv StateUniversity (Ukraine) in 1976. She is a leading engineer at Carat. Her scientific interests are materials science engineering and amorphouschakogenides. Mykola Vakiv has a Ph.D. in engineering and was born in 1952.He graduatedfrom the OpticsDepartmentofLviv State University (Ukraine) in 1974.He is generaldirector of Carat. His scientific interests are materials science engineering, degradationprocessesin solids, and sensorsand actuators. Lyubov Shpotyuk was born in 1960. She graduated from the Energetic Department of Lviv Polytechnic University (Ukraine) in 1982. Sheis scientific secretary of Carat. Her scientific interest is solid-statematerialsfor electronics.
ELSEVIER
Sensorsand ActuatorsA 68 ( 1998) 356-358
PHYSICAL
Sensorsof high-energy radiation basedon amorphouschalcogenides 0.1. Shpotyuk a7b,*,V.O. Balitska a, M.M. Vakiv a, L.I. Shpotyuk a aLviv Scientific Research Institute of Materials, Stryjska St. 202, UA-290031, Lviv, Ukraine h Physics Institute of Pedagogical University of Czestochowa, Al. Armii Krajowej 13/15, PL-42201, Czestochowa, Poland
Abstract Possibilities of practical application of amorphouschalcogenidesemiconductorsobtained in the form of bulk glassesasradiation-sensitive elementsof solid-state dosimetric systemsfor high-energy ionizing radiation are analysed. It is establishedthat the most suitable for this 0 1998Elsevier ScienceS.A. All purposeare sensorsbasedon the electrical and photoelectrical propertiesof the investigated materials. rights reserved. Keywords: Amorphous chalcogenide semiconductors; Radiation sensors; Photoconductivity
1. Introduction
Optical dosimetric systemsbasedon amorphouschalcogenide semiconductors (AChSs) can be used for radiation measurements in a wide range of absorbed doses (from 1O2 to IO7Gy) of high-energy ionizing radiation [ 11.Suchradiation sensors are characterized by a low barrier of information bleaching (440-470 K) [2] in comparison with widely used
ones based on coloured oxide glasses [ 3,4] I The physical principles of their functioning areso-calledradiation destruction-polymerization transformations accompaniedby concentration changesof coordination defects,studied in detail using the far-JRFourier spectrometrytechnique [ 5-81. The optical properties of AChSs, first of all the optical density D in the middle point of the upper part of the fundamental optical transmission edge, being tightly connected with their defectstate,dependmonotonically on theabsorbed dose @in agreementwith the expression ADID,=Slg@+A
(1)
where A is some constant for a specific AChS composition and S is the device sensitivity. However, it is well known that the electrical and photoelectrical properties of AChSs are also determined by the coordination-defect concentration [ 91. Hence we suppose
that the level of radiation influence can be estimatedarising from radiation-induced defect changesin the sameway. It mustbe noted that a similar principle of functioning is proper
to radiation sensorswith sensitiveelementsmadeof crystal* Corresponding author. Tel.: + 7-380-322-634-205; Fax: + 7-380-322632-228; E-mail: [email protected]
line semiconductors,but they have a low level of registered dosesand sensitivities [ 3,4]. We shall consider in this paper the new experimental results obtainedusing AChS samples in the form of bulk As,Se,-basedchalcogenide glassesin order to confirm this supposition. 2. Experiments
Investigated AChS samples of ( As,Se,),(Sb,Se,) I --x (0.75 2x5 1.OO) compositions were prepared from highpurity elementalconstituentsby direct synthesisin evacuated quartz ampoulesasdescribedpreviously in Refs. [ 5-81. The standardrocking furnace techniquefollowed by air quenching was applied. After synthesis all ingots were cut to 1 mm X 1 mm X 5 mm parallelepipeds.It was confirmed by Xray diffraction measurementsthat phaseseparationand crystallization are absentin the samples.Two kinds of samples were selected for experimental measurements: freshly obtained and previously thermoannealedin air (at T= 420430 K for 3 to 5 h). The dosimetric characteristicsof bulk AChS samples were studied after irradiation by y-quanta from a 6oCosource. The dark electrical conductivity u and maximal intensity of spectral photoconductivity aPhwere used as radiation-sensitive parametersin our experiments
[lOI * 3. Results
The main characteristicsof radiation-sensitive dosimetric systemsbasedon As,Se, chalcogenideglassesarepresented in Table 1.
0.1. Shpotyuk et al. /Sensors
and Actuators
357
A 68 (1998) 356-358
Table 1 Dosimetric characteristics of As,Se,-based chalcogenide glasses Radiation-sensitive element
Control parameter
Range of doses A@, Gy
Sensitivity S, au.
Freshly obtained Freshly obtained Thermoannealed Thermoannealed Freshly obtained Freshly obtained Thermoannealed
Au/a<0 Au/u<0 Ada>0 Ada>0 Au,,lu,,
5x105-5x106 5 x los-5 x 106 7.5 x 105-10’ 5 x IO”-2 x 10’ 3x los-2x IO6 3 x lo”-2 x 106 3 x lOj-5 x lo6
0.06 0.15 1.00 0.34 0.65 0.95 0.87
A&Se3 bulk glasses (As,Se,),,,(Sb,Se,)~,~ glasses As&Se, glasses (AsaSe3)085(Sb2Se3)0 ,s glasses As,Se, bulk glasses (As,Se,), so(Sb,Se,),,,, glasses As,Se, glasses
Not all our investigated radiation-sensitive elementscan be used repeatedly becauseirreversible radiation-structural transformations were produced by chemical interaction of absorbed impurities and the destroyed units of the glassy network aretoo high for thesecompositions [ 111.Apartfrom this feature,As,Se,-basedelectrical dosimetric systemshave a relatively narrow range of registereddosesin comparison with AChS-basedoptical sensors[ 11. The dosimetric characteristicsof such sensorsare quite reproducible in the wide range of preparation conditions. Only thermal annealing has a significant influence on thesesensors. It is establishedthat freshly obtained As,Se,-basedchalcogenide glasses are characterized by negative radiationinduced changes of control parameters. The maximum sensitivity Sdoesnot exceed0.15 in the caseof dark electrical conductivity measurements,while it is approximately equal to 1.Ofor aphmeasurements.Chalcogenideglassespreviously thermoannealedat a temperature near the glass transition point have higher sensitivities for both u and oPhmeasurements.Thus AChSs obtainedby the traditional direct synthesis methodhave predictable sensitivity characteristicsbut the thermal annealing conditions must be taken into account.
4. Discussion Solid-state dosimetric systemsbasedon freshly obtained and previously thermoannealed(As,Se,),( Sb,Se,) 1--xchalcogenideglassesare characterizedby high sensitivities to yirradiation of the 6oCoradioisotope. Taking into account experimental results on the microstructural mechanismof radiation-inducedtransformationsin AChS [ 7,8], we conclude that the observedchangesof dark electrical conductivity c and the maximum value of spectral photoconductivity aPhare mainly connectedwith coordination-defect formation processes.But impurity radiationchemical interactions led to the formation of OH-, CH- and CO-containing complexes [ 111which play an important role too and explain the irreversibility of the investigatedsensors. Coordination-defect formation processesare associated with chemical-bond switching [ 7,8]. Instead of a chemical bond being destroyed,another one forms and the balanceof the new bondsis stabilized in the glassstructure.The number of covalent chemical bonds is not changedduring this proc-
ess,but the mean energy of the bond network may reach a new level different from the initial one.Moreover, two point defectsappearin the neighborhood with transformedbonds, over- and under-coordinated atoms having uncompensated negative andpositive charges.It is supposedthat the microstructural nature of coordination-defectformation in AChS is explained by exciton self-trapping [ 121 or excitation of socalled soft atomic configurations [ 131.
5. Conclusions The dosimetric characteristicsof As&-based chalcogenide glassesfor y-irradiation measurementshavebeenstudied. It has been shown that these materials can be conveniently usedasradiation-sensitive elements.The dark electrical conductivity and the maximum value of the spectralphotoconductivity are expected to be the most suitable control parametersof these sensors,characterizedby the necessary reproducibility of measurementsand high sensitivity. But irreversible effects causedby radiation-structural transformations limit the repeateduse of AChS sensors.The microstructural mechanismof suchtransformationsis basedon the coordination-defect formation processesand chemical-bond switching.
References t11 0.1. Shpotyuk,
Amorphous chalcogenide semiconductors for dosimetry of high-energy ionizing radiation, Radiat. Phys. Chem. 46 ( 1995) 1279-1282. [21 0.1. Shpotyuk, Temperature stability of gamma-induced effects in vitreous arsenic trisulphide, Zh. Prikl. Spektroskopii 46 ( 1987) 122126. [31 A.K. Pikaev, Modern Radiation Chemistry, Main States, Experimental Technique and Methods, Nauka, Moscow, 1985, p. 375. I41 M. Frank, B. Shtolz, Solid State Dosimetry of Ionizing Radiation, Atomizdat, Moscow, 1973, p. 247. [51 0.1. Shpotyuk, A.P. Kovalsky, M.M. Vakiv, O.Ya. Mrooz, Reversible radiation effects in vitreous AsaS,, Phys. Status Solidi A 144 ( 1994) 277-283. I61 0.1. Shpotyuk, A.O. Matkovskii, Radiation-stimulated processes in vitreous arsenic trisulphide, .I. Non-Cry& Solids 176 (1994) 45-50. [71 0.1. Shpotyuk, Mechanism of radiation-structural transformations in amorphous As&, Rad. Eff. Defects Solids 132 (1994) 393-396.
358
0.1. Shpotyuk et al. /Sensors and Actuators A 68 (1998) 356-358
[81 0.1. Shpotyuk,
Reversible radiation effects in vitreous A&. 2. Mechanism of structural transformations, Phys. Status Solidi A 145 ( 1994) 69-75. [91 A. Feltz, Amorphous and Vitreous Inorganic Solids, Mir, Moscow, 1986, p. 558. 1101 A. ROW, Photoconductivity Principles, Mir, Moscow, 1966, p. 192. 11110.1. Shpotyuk, Spectroscopic study of penetrating radiation influence on surface of vitreous arsenic chalcogenides, Ukr. Fiz. Zh. 32 ( 1987) 509-5 12, 1121R.A. Street, Non-radiative recombination in chalcogenide glasses, Solid State Commun. 24 (1977) 363-365. [I31 M.I. Klinger, Model of electronic processes in glassy semiconductors: correlation with structural features, Solid State Commun. 45 ( 1983) 949-953.
Biographies Oleg Shpotyukwasborn in 1958and is a Doctor of PhysicalMathematical Sciences.He graduatedfrom the Materials ScienceDepartmentof Lviv StateUniversity (Ukraine) in 1980.
He is the researchdirector of the scientific researchcompany Carat (Lviv, Ukraine). His scientific interests include materials scienceengineering and defect-formation processesin disorderedsolids. Valentina Balitska wasborn in 1954.Shegraduatedfrom the SemiconductorPhysicsDepartmentof Lviv StateUniversity (Ukraine) in 1976. She is a leading engineer at Carat. Her scientific interests are materials science engineering and amorphouschakogenides. Mykola Vakiv has a Ph.D. in engineering and was born in 1952.He graduatedfrom the OpticsDepartmentofLviv State University (Ukraine) in 1974.He is generaldirector of Carat. His scientific interests are materials science engineering, degradationprocessesin solids, and sensorsand actuators. Lyubov Shpotyuk was born in 1960. She graduated from the Energetic Department of Lviv Polytechnic University (Ukraine) in 1982. Sheis scientific secretary of Carat. Her scientific interest is solid-statematerialsfor electronics.