Radiation-induced defects influence on the electrical, photoelectrical and optical properties of chalcogenide glasses

Journal of Non-Crystalline Solids 35 & 36 (1980) 877-882 ©North-Holland Publishing Company

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R..LIATION-INSUCED DEPECTS i~FLUEIiCE i~I~CTRICAL,PHOTOgLECTRICAL ~I~D OPTICAL PROPERTIES OF CH~LCOGE~IDE GLASSES

S. S .Sat sembinov ,~ .E .Abdulgafar ov ,if.A • r~ I t~lanov, ~ .A .R oga chev* Kazakh S gate University ~ima-Ata,USSR

High-energy (2 Mev) electron irradiation of vitreous ~soS%,J~sgSe%,As~Se o and GegS % produces the effect, cofr@lat~ng~wit~ photodark~ning and photoatructural effects. The increase of conductivity value and photoconductivity response due the electrodes matter were obserwed.Radiation-induced changes are depends of the glass composition and annealing. 2hotoconductivity amplification effect in vitreous As2Se 3 samples, depending of the photon energy and electric field,,vere also investigated. II'~Ti{0LbOTlOi~ The current paper presents the results of ~ e s t l o a ~ z o n of some c!ectrical,photoelectrical and optical properties of vitreous ~s~S~,as~Se~,As~Se.~ and Ge2So after high-energy electron inradiatiSn~and~(H~-Ne~ l~ser beam ~ll~::ination. mXPERIL~NT~L RESULTS ]ieasurements were carried out on bulk samples sandwich type. El, Cu,~g,_~u,~e,ln and C were used as electrcdestZlectrodes were prepared by thermal evaporation in vacur~ 2 10 -~ Torr. Carbon was daubed as a paste. Samples were irraQiated with 2 ][ev electrons from a linear accelerator. ~lectron fl'~x density d~uring irradiation was ]013 o cm-2sec -1. The samples were irradiated by the integrate flux of 1017 e cm -2. The temperature of the samples were not exeod 30OK. Diffusive concentration profiles measurements was made by means of roentgenospectral microanalysator "C~,D~CA"-}IS-46. Radiation-induced defect structure was investigated by means of positron annihilation technique. Irradiated samples annealing was made during I0 h at 160 C in vacuum 10-3 Torr. 1.Electrical and photoelectrical properties. it was stated, that before electron irradiation the conductivity value and its temperature dependence of all investigated chalcogehide glasses do not depend on electrodes matter. However,after irradiation the strong increase of conductivity value and change of temperature dependence of conductivity were observed (Sarsembinov and i~bdulgafarov (1977,1978)). Eoreever,it was shown, that the increase of conductivity to a great extent depend on electrodes matter. ~s Fig.la shows, in the case of As2S ~ the most strong rise of conductivity is observed in the samples, @upplyied with i~i elec ~rodes. The In and C electrodes influence on tile conductivity of ,Present address: ~.F.loffe Physics-Technical institute,Leningrad.

877

S.S. Sarsembinov e t a l .

878

/ Radiation-Induced

Defects Influence

irradiated samples least of all. According to the present data favourable conditions are created for electrodes matter diffusion into irradiated glass matrix. This may be confir~ed by average on volume diffusive concentration profiles of Fe,Bi,.~u and Cu in As2S3, represented in i,'ig.lb. As that i:igure shows, there are "~hrough diffusion', of electrodes matter through the irradiated glass matrix Annealing of irradiated glass matrix without the electrodes restores it conduction properties.

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Figure I a - temperature dependence of conductivity in ~soS ~ before irradiation(1),after irradiation with Bi(2),Tn~3) and C(4) electrodes ~ b - diffusive concentration profiles of Fe(1),Bi(2),Au(5) and Cu< .) in AsoS~; e - spectral depend@tales of oi±otooonductivity in ~soSo with Bi electrodes before(1) and alter
879

S.S. Sarsembinov et el. / Radiation-Induced Defects Influence

composition are represented at Table I. 2he annealing at 160°0 (~'.~ig.2a,b,c,d) showed that l~adiation-induced cksu~iges of optical properties are incompletely reversible in the case of As2S 3 and As3Se2, and completely reversible - at vitreous Ge2S 3. Thus there is essential inr!uence of chalcogenide glass composition on the value and aS(ev) reversibility of electroninduced changes of the opti25 o.i :~s2S} cal prepe~'ties. =~ii represented at Table I para~eters in 25 0.0~ ~ssSe 2 the composition with arsenic <5
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:,'igume 2. spectral Yepondences of transmission coe Cficisnt in As S (a) ,J~s3Se2( c) an£ GeeSe(b) befoz'e(1 and after(2) irradiation-she after ann@a~ing(3). comparatively

smell and irreversibly.

3.£ositron annihilation in vitreous Aso5 ~. It was stated, that after high-energy ~l~ctron irradiation the area under Oaussian part of ansle disti~ibution curves of annihilated - quantu4"~s is increased, and under parabolic part- is decreased. It means, that the ntuzber of positron annihilation acts with bonding electrons a~e increased, i~egativo charge defects oocentrutien, based on the work (Sarsembinov and ebdulgafarov(1979b)) equal before irradiation Ii°=0.8.I017 cul-~, after irradiation -~{~= 1 .3-1017 cm -3.

880

S.S. Sarsembinov et al. / Radiation-Induced

Defects Influence

4.Laser beam illcm~ination influence on the photoconductivity of vitreous AsoSeo. 2hotoconduc~iv~ty amplification effect (Pig.3a,b) in vitreous i~soSe~ samples under simultaneous ill~r,lnation by monochromatic light'with the w a v e l e n g t h ~ i and He-:Se laser beam (~ =0.63~m) is observed. b

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i~'igur e 3 a - measuring scheme; b - illustration to measuring £igure 4 shows amplificatio~ coefficient "~(" spectral dependences for various electric field(Fig.4a) and for various laser beam i~tensity(Fig.4b)

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Fig uuve 4 Photoconductivity aHplification coefficient spectral dependences: a - !~ ....^:const, 1-L:50v/cm,2-~=150v/cm, 5-E=1500v/cm; b - ~=c~nst=1500vlcm, !1=412(~ie-Ne). As Fis.4 show, there are a certain dependences of 9hotoconductivity amplification coefficient from the wavelength and intensity of incident light and from the electric field ntrenth. 2hotoco~ductivity amplification effect presence in vitreous As2se ~ and its features with electrio field may be describe from the point of view of recombir~ation process changes due near conduction hand edge local tragping centers activization ~]~.~ring laser beam i l l ~ i n a t i o n .

S.So Sarsembinov et al. / Radiation-Induced

Defects Influence

88]

DIS CUSb ICY .~ccordin C the obtained data essential changes of various properties of chalcoc~nidc glazses after high-enerc7 electi~on irradiation and laser beam illmnination may be conditioned b$~ locel structural transformations in glass matrix due radiation-induced defects for~mtion. it is knov,,n, that defect conc~ntr'~tion may be strongly increased under some external influence. ,~e suggest that in cha±cogenide glasses radiation-inauced defects - is the excess negative charge centers by C~- type or local accumulation(clusters) of these centers. If this st<~position is correct, then the observed experimental data will be explained within the Kastner,Adler end Fritzsehe (1976) model framework. The chemical bonds in glass matrix are broken under irradiation mainly beetween the atomic chains, but it is possible brolcen bonds formation inside the chains. Thus the chaleegehide or arsenic atoms transfer from bonding ~tates to end of chain states. This 9roce~s can be sche:mticallv represented at the following forms: C+ ~ C~ and C°~ C~ . So in chalco~enide glasses can ar~se ~xceso negative charge de±acts concentration,sufficient Dart of which do not readily anneal at 3OOK. These excess defects can be distributed locally, transfo~ming nearest-neishbouring local bonding configurations, or groups in the cluster for::s, ess~ntially changing energy s p e c t r ~ of carriers (for exsmole, forming a deep trace anC recombina$ion centers,color centers end so on). ~]xcess defects o~' cluster type presence can be lead to intensive diffusion of the electrodes r~mtter.%eep into irradiated gl
882

S.S. Sarsembinov et al. / Radiation-Induced

Defects Influence

more higher covalent coordination in comparison ~;ith arsenic contained cha!cogenide olasae~, ma~ !~ad to accidental distribution of charge defect centers an~, consequently, to ~ore low concentration of transforming local bonding configurations, in results, these local bonding configurations are transformed without the potential barrier creation, a~d radiation-induced changes of physical properties are reversible. !~ote, that excess radiation-induced charge defects influence and formation, which connected with carriers generation, obviously, prevail over atomic displacement processes.Positron annihilation data in As~S~ confirmed its and showed that concentration of negative charg@ ~efects is increase after irradiation, and,in addition, electron spin resonance response at 30OK was absent (Tayl6r,Strom a~d Bishop(1978)).

[1]oarsembinov,S.S.and Abdulgafarov,~.2.,in: Fizika sto~mogo yadra i kosmicheskih luchey (Ka~U,~lma-~ta,19 7) 186. [2]Sarsembinov,S.S.and Abdulgafarov,E.E.,in: Proc.of Internat.Conf. "Amorphous semiconductors'78" (Pardubice,1978) 379,499. [3]Sarsembinov,S.S.and Abdulgafarov,E.E., Izvestiya ~2~ KazSSR.Seriya fiz.-mat., (1979) to be published. [4] Lyubin ,V.I~.,in: ?roc. of Internat. Conf. ";~morphous semiconductors' 78" (Pardubice,1978) 20. [5] Sarsembinov,S .S .and Abdulgafarov,E.E., Vestnik A~ XazSSR,(1979), to be published. [6]Kastner,H.,Adler,D.,Fritzsche,H.,fhys.Rev.Lett.,37(1976) 1504. [7]~astner,l~., Phys.Rev.Lett., 28 (i972) 355. [8] Taylor,P.C.,Strom,O.,Bishop,S.G., Phys.Rev.B, 18 (1978) 511.