RADIATION-INDUCED DEFECTS FORMATION IN CHALCOGENIDE GLASSES

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RADIATION-INDUCED DEFECTS FORMATION IN CHALCOGENIDE GLASSES

Sh. Sarsembinov, E. Abdulgafarov, K. Tolkanchinov

To cite this version:

Sh. Sarsembinov, E. Abdulgafarov, K. Tolkanchinov. RADIATION-INDUCED DEFECTS FORMA- TION IN CHALCOGENIDE GLASSES. Journal de Physique Colloques, 1981, 42 (C4), pp.C4-915- C4-918. �10.1051/jphyscol:19814199�. �jpa-00220826�

JOURNAL DE PHYSIQUE

CoZZoque C4, s u p p l l m e n t a u nO1O, Tome 4 2 , o c t o b r e 1981 page C4-915

RADIATION-INDUCED DEFECTS FORMATION I N CHALCOGENIDE GLASSES

Sh.Sh. Sarsembinov, E.E. Abdulgafarov and K. Tolkanchinov S.M. Kirov Kaaakh S t a t e U n i v e r s i t y , 480091, Alma-Ata, U . R.S. S.

Abstract.- ilign-energy (2;,ev) electron irradiation may produce excess density of valence-alternation pairs (VAY1s) in chalco- genide glasses. Relativistic electron energy losses and non- equilibrium density of radiation-induced "atomic shiftudefects in vitreous As S and As2Seg are calculated. Zadiation-induced defects formatgo2 scheme is proposed and compared with posit- ron annihilation data. It is shown that radiation-induced de- fects may cause essential changes in electrical and optical properties of chalcogenide glasses.

Zelativistic electron (C. 5 < E

<

lO?.Tev) irradiation lead to ef - fective structural changes in chalcogenide glasses, becouse high- energy electrons are capable to cause both atomic electron shells ionisation and "atomic shiftu defects formation. As calculation show practically each atom is ionised during 2 :Lev electron irra diation in vitreous As S and As2Se3. Znergy losses in these materi-

2 3

als amount to -dE/dx= 0.35.,~ev/nlrn and 0. 49A;-ev/m,respectively. Obvio- usly, deep shell electrons ionisation may not cause irradiated glass matrix structural cha~des. tiowever,high-energy electrons ionise only atonric valeme electrons to the conduction band after energy losses in some caskade -1rocesses. In this case chemical bonds are broken, binding peculiarities are affected and new structural defects are formed. Ve suppose that ioiiising effect of electron irradiation re- sults in excess density of the existing charge defects C ; and C; ac- cording to the scheme:

2c;

-

^2(c;)*

-

^2c;

^{- c; + c; .}

Electronic configurations for that reaction represented in the fol- 10~~ving figure (only for p-electrons ) :

...etastable states of cheloogen atom (C;)* exist only during the elec- tronic irradietion. After the irradiation one of lone-pzir electrons snould better pass into the bonciinr state fonin; a C; defect center

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19814199

C4-9 16 JOURNAL DE PHYSIQUE

which transforms into charged defects according to the well known valence-alternation pairs forming reaction( 1 ).

Relativistic electron irradiation of chalcogenide glasses pro- duces some "atoinic shiftu defects density too. 2 Mev electrons dis- sipation differential cross sections (

d

,,) and "atomic shift" defect densities (iV) for the glass network elements (As2S3 and As2Se3) in table 1 are given. Bere atomic shift energy threshold is supposed to be Ed-25ev, and =

6

I (according to the(2)), where Y - coeffi-

D 0

cient with the caskade process taken into account, I=10 17

No=

3x 1 0 ~ ~ 8 6 ~ . EA

-

the m a x i m u energy, which is transferred from the bombardment electrons to atomic nuclei

Table 1. It should be noted that N

Element EA ev

6

^{D, sme2 3 , srn-)} is the non-equilibrium de- fects density in the sample S 402 2. 10-20 _4.9 1020 under irradiation.After the irradiation turned off the Se 163 1.1 2.5

lo2'

radiation-induced def act

concentration decreases to AS 172 3*7 2*7 lo*' a certain stationary value due to the some relaxation processes and self-recombination.For exam- ple, positron annihilation data showed that C; defects equilibrium density is 1.3*10~~srn-~ at 300K after 2 MBV electrons irradiation with dose of 10 s

17

*m' (before irradiation

-

^0.8 10~~srn-~)(3).

Thus it may be supposed that high-energy electrons irradiation of chalcogenide glasses gives rise to the excess valence-alternation pairs defects density, essentially affecting their electrica1,photo- electrical and optical properties.

Por instence, we found that conductivity and photoconductivity values of some chalcogenide glasses increase by several orders of magnitude due to a peculiar electron-enhanced electrode matter dif- fusion to the glass matrix ( 4 ) . We think, that it takes place as a result of specific nature of interaction between additive elements and radiation-induced VAPts defects. So, the following situation may arise from the electron-enhanced diffusion of the Periodic Table I group elements(Cu,Ag,Au

-

Me) to the glass bulk:

(a) additive atoms may form two normal covalent bonds with the glass network elements becouse one d-electron passes into the p-shel1,lie- ing at a short energy distance from the d-shell (for Cu

-

^{from the}

3d to 4p-shell) (dp-hibridization):

0

c0

dp:vle2

+

^2~:

-

^'a.

^-.,

^B

where the subscript denotes the element valency, and the superscript denotes additive toms charge states;

(b) the large probability exist that empty orbitals of additive atoms

;nay be occupied by C; centers lone-pair electrons. So the following reaction takes place: ~~isie;

+

C;

-

^{2Mei + C;}

^.

This reaction is the source c f excess holes, and all d-orbitals are filled.

Similarly, the inte-action of additive elements of other groups with

CT

defect centers may be described (in accord'ance with(5)):

I?e0 + 2 ~ ;

-

^~e:-

⁺

2 ~ ' and 2,ai;

+

3 ~ ;

-

2 ~ i z -

+

3 ~ ;

,

d 4 3

where ~ e i - and 3iz- -"inert ionsbb, not forming chemical bonds and not displaying electrical activity in the glass matrix.

At large additives densities the C; centers conversion to the C+ centers gives rise to extrinsic p-typo corld-uctivity irrespective

3

of the additive elements origin (the I or 5 group of the Periodic Table or transition elements). The latter is confirmed by thermoemf sign measurements. iie suppose that specific nature of effective in- teraction between additives elements and charged defect centers re- sult from high electropositive properties of C; centers (becouse of two lone-pair electrons), whose density in the irradiated glass mat- rix increases considerably.

Tie radiation-induced C; centers conversion to C+ centers for the I11 group elements (In,Ga,Al) is hindered, becouse empty orbitals 3

are absent. So electren-enhanced modification of chalcogenide glas- oes plectric properties in that case is not realized ( 5 ) .

The radiation-induced defects formation caused changes in chalcogenide glasses optical properties. Por vitreous As,S and

3 ^{r 3}

AspSe3 the exponential plot ( & =lo-10 sm-I ) of optical absorption edge before and after the electron irradiation in figure 1 are given.

After 2 Idev electronic hombardmont ( 1 ~ 1 0 17 sm'2) the exponential cha- racter of absorption is unchanged and its edge shift to the long wavelenth range is observed. The absorption edge slope (S) decreases from 22ev-I to 1 gev-I

-

for As Se and from l8ev-I to 15ev-I

-

^for

2 3

As2S3. The high-energy electrons irradiation influence on the elec- troabsorption spectral dependences are illustrated by figure 2.

Electroabsorption signals decrease as a result of irradiation: 1.4 times (near h@ ^{=I ,5ev)}

-

^{in 2 times (bW =2.0ev)}

-

^{in As2S3}

.

It is concluded that thettS" and " b & / & F 2 decreases can be as- cribed to growth of intrinsic field value

(Y2)

in the equation

4&/&r2=

~ ( b

- ~ ~ ) e ~ / 3 ~ ~ (in accordance with(6)). which is due to the fact that irradiation produces excess C; defect centers density.

JOURNAL DL PHYSIQUE

Fi 1 : Spectral dependences of Fig.2 : Electroabsorption spectral a a l abeorption in vitreous dependences in vitreous As,S, and As S, and As ,So, before(1) and As,Se, before(1) and after121 elec- after(2) eleCtrbn irradiation. tron irradiation.

References

1 Kaetner PB. ,Adler D. ,Fritzsche ii, Phyrr. Rev.Lett. 37 (1 976) 1504.

2 Kelly B.T. Irradiation damage to Solids, Pergamon Press ,it. Y. ,1965.

3 Sarsembinov Sh. Sh. ,Abdulgafarov E.E.

,

Vestnik Ad KazSSR,2 (1 980 )48.

4 Sareembinov Sh. Sh. ,Abdulgaf arov E. E.

,

T m a n o v I&. A. ,Rogachev N. A.

Journal of Non-Crystalline Solids, 35-36 (1980) 877.

5 Sarsembinov Sh. Sh. ,Abdul&afarov E.E. ,Vestnik AN KazSSR, 5 (1 981 )51.

6 Esser B. Phys.Status Solidi, 51 (1972) 735.