Electrical and optical properties of chalcogenide glasses with non-tetrahedral coordination

Journal of Non-Crystalline Solids 111 (1989) 277-284 North-Holland, Amsterdam

277

ELECTRICAL AND OPTICAL PROPERTIES OF CHALCOGENIDE WITH N O N - T E T R A H E D R A L C O O R D I N A T I O N J. O L I V I E R - F O U R C A D E ,

GLASSES

A. B O U A Z A , J.C. J U M A S a n d M. M A U R I N

Laboratoire de Physicochirnie des MatOriaux UA 407, Universitd des Sciences et Techniques" du Languedoc, Place EugOne Bataillon, 34060 Montpellier Cedex, France

Received 6 February 1989 Revised manuscript received 15 June 1989

Electrical conductivity, edge absorption and infrared transmission have been measured for Sb2S3-TI2S and chalcogenide glasses as a function of glass composition. The electrical conductivity of the glasses of the two systems ranges from 10 - 6 tO 10-9 ~(2 1 cm 1 at 200 ° C which indicates that these glasses are semiconductors. The variation of the activation energy indicates a change in the conduction mechanism. The optical gap values are 1.65 to 2.16 eV which class these glasses among wide-gap materials. These glasses possess a wide optical window that is maximum (12.66 /~m) for the 0.8 Sb2S3-0.2 TI2S glass. A s 2 S 3 additions cause an infrared cut-off decrease from 13.3 to 11.36 /zm. Sb2S3-As2S3-T12S

1. Introduction Vitreous m a t e r i a l s have t h e r m o p h y s i c a l a n d m e c h a n i c a l p r o p e r t i e s that m a k e t h e m s u i t a b l e for m a n y a p p l i c a t i o n s in various devices using light wave emission, t r a n s m i s s i o n or detection. T h e s e device functions d e p e n d on o p t i c a l a n d electronic characteristics, such as the electrical c o n d u c t i v i t y , the gap w i d t h a n d its nature. T h e c h a l c o g e n i d e glasses offer a range of i n f r a r e d t r a n s m i t t i n g m a t e r i a l s that are t r a n s p a r e n t in the w a v e l e n g t h regions of 3 - 5 /~m a n d 8 - 1 4 /~m. C h a l c o g e n i d e glasses also have a high refractive index, low optical losses a n d their p o s s i b l e a p p l i c a t i o n s as inf r a r e d o p t i c a l m a t e r i a l s have b e e n discussed recently [1,2]. This p a p e r a t t e m p t s to collect a n d correlate recent w o r k a n d discuss the p r e p a r a t i o n , electrical a n d optical p r o p e r t i e s for S b z S 3 - T l z S a n d SbzS 3As2S3-T12S glasses in which Sb or As shows n o n - t e t r a h e d r a l c o o r d i n a t i o n [3].

q u a n t i t i e s of h i g h - p u r i t y (99.999%) elements. The glass s a m p l e s were p r e p a r e d b y m i x i n g the app r o p r i a t e a m o u n t of the b i n a r y c o m p o u n d s . The c l e a n e d silica tubes c o n t a i n i n g the m i x t u r e were e v a c u a t e d to 10 -5 T o r r a n d sealed. The c o n t e n t s of the tubes were m e l t e d in a furnace a n d cont i n o u s l y a g i t a t e d d u r i n g 16 h to ensure g o o d homogeneity.

As2S3 5

O 10 19

•

Glass

o

Crystalline

4

21

28

2

32

3

2. Glass preparation Binary c h a l c o g e n i d e s Sb2S 3, As2S3 a n d T12S were p r e p a r e d b y direct r e a c t i o n of a p p r o p r i a t e 0022-3093/89/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

Sb2S3

TI2S

Fig. 1. Identification of the various compositions studied in the Sb2S3-AszS3-TI2S system ( e = g l a s s composition: © = crystalline compound).

J. Olivier-Fourcade et al. / Electrical and optical properties of chalcogenide glasses

278

In the base system S b 2 S 3 - T 1 2 S the melt was rapidly quenched in ice-cold water from 9 0 0 ° C and the cooling rate was estimated at 1000 K s 1. In the Sb2S3-As2S3-TlzS system the melt was, in most cases, slowly cooled in the furnace by interruption of the heating, the initial temperature was 7 0 0 ° C and the cooling rate was 0.5 K s -1 [4]. Ingots obtained were annealed at a temperature 50 ° C below the glass transition temperature for 20 h. The amorphous nature of the samples was checked by X-ray diffraction and scanning electron microscopy. The compositions studied and their identification numbers are shown in fig. 1.

dynamic vacuum between 100 and 250 ° C. Electrical conductivity results were repeatable to within 1%. The optical absorption measurements were performed using a Beckman A C T A M I V spectrophotometer operating at room temperature in the spectral range 0.2-0.5 /Lm. The samples were homogenous pellets of thickness 0.3 m m made up of a glass powder and a KBr mixture where the glass concentration is 2% W / W . The infrared transmission measurements were carried out using a Beckman I R 4260 spectrophotometer operating at room temperature in the spectral range 2.5-50 /~m. The studies were performed on polished disk-shaped specimens having thicknesses between 2 and 4 mm.

3. Property measurements Electrical conductivity measurements have been carried out on the vitreous samples by the complex impedance method as indicated in ref. [5], using a H e w l e t t - P a c k a r d 419ZA frequency response analyzer. The samples used were pellets 0.5 m m thick with surface area 1.33 cm 2 prepared by applying a pressure of 9 t o n / c m 2 for 10 min to the glass composition powdered by mechanical milling. Silver paste was used for electrical contacts. The frequency range used is 5-13 x 10 3 Hz and measurements have been carried out under

Logo,

4. Results and discussion

4.1. Electrical conductivity The temperature dependence of the electrical conductivity is plotted in fig. 2. The electrical conductivity can be expressed in the temperature range considered by an Arrhenius-type relation o ( T ) = % e x p ( - E a / k T ) where E a is the activation energy and % is the conductivity pre-exponential factor. The activation energy and the conductivity at 1 8 0 ° C are presented in tables 1 and 2.

4.1.1. S b 2 S 3 - T I 2 S glasses

(f/cn~

In the system Sb2S3-T12S , it is observed from fig. 3 that there is an increase in conductivity with increasing T12S content in the samples, with the exception of glass number 12.

-5

-7

-8

-'~*~°~,

• ~

Table 1 Data on E a and O18oOc of Sb2S3-T12S glasses studied

19

-9 2.25

-?.(K)

Fig. 2. Log conductivity (in 12 1 c m - l ) as a function of 1 / T (K) of some glasses in the Sb2S3-TlzS (a) and Sb2S3-AszS3TlzS (b) systems. The compositions are identified by the numbers noted in fig. 1.

No.

Sb2S3-T12S

E a (eV)

o180oc (12 cm) -1

log als0O c

20 13 12 11 6

0.75-0.25 0.80-0.20 0.83-0.17 0.86-0.14 0.95-0.05

1.58 2.08 1.00 0.96 1.1

1.1 × 106.8×10 3.0X 10 3.5 × 10 1.7 × 10

-- 5.96 -6.17 -6.52 -6.46 -6.77

6 v v 7 7

J. Oliuier-Fourcade et aL / Electrical and optical properties of chalcogenide glasses Table 2 D a t a on E a a n d a]8oo c of

279

>

"-"

Sb2S3-As2S3-TI2S glasses

studied

No.

Sb2S3-As2Ss-T12S

Ea (eV)

0180 ° (J2 c m - 1 )

log a]soo ¢

13 15 16 17 19

0.8-0-0.2 0.5-0.3-0.2 0.35-0.45-0.2 0.2-0.6-0.2 0-0.8-0.2

2.08 1.02 1.55 1.83 1.87

6.8 x 10 - 7 10.6x10 -9 2.2 x 10 - 9 1.5 × 1 0 - 9 1.1x10 -9

- 6.17 -7.98 - 8.65 - 8.82 -8.97

The composition 0.83 Sb2S3-0.17 T12S, situated in the region where the glass-forming ability is m a x i m u m [6], corresponds to the T1Sb5S 8 crystallized phase [7]. For this composition the glass and crystal conductivities are of the same order glass ~'2- l crystal o ] 8 0 o c = 3.0 x 10 -7 cm - t and o]80o c = 2.2 X 10 7 ~-~- c m - I [8]). T h e crystal structure of TISbsS 8 which shows 10 distinct crystallographic sites for Sb [7] probably approaches the glass structure and explains the similar conductivities. The conductivity of glass n u m b e r 6 (0.95 8b2S3-0.05 TI2S , O]8ooc = 1.7 X 1 0 - 7 ~ 1 c m - 1 ) is lower under the same conditions, than that of c r y s t a l l i z e d S b 2 S 3 ( 0 1 8 0 o c = 2.5 × 10 -5 12- t cm t, [91). It appears from fig. 4, that the evolution of the activation energy is not continuous with the corn-

13

ua~

2

/'.20

sb2s 3

¢o

2~

%TI2S

a'0

Fig. 4. V a r i a t i o n of the a c t i v a t i o n energy for electrical conduction E a as a function of the T12S c o n c e n t r a t i o n in the Sb2S 3 -.T12 S glass system.

position. The activation energy between 100 and 83.3 mol% Sb2S 3 is of the order of 1 eV and beyond 83.3 it becomes higher, 1.5 to 2.0 eV. This implies a change in the conduction mechanism.

4.1.2. Sb2Ss-AseS3-0.20 Tl:S glasses The electrical conductivity of the glasses belonging to the Sb2S3-As2S3-0.20 TI2S section

Logo(f~cm)-I

L, go(Ocm) -1

-6113 20,

-6

13/°

-" 2js

o

/°\

-6.5

~16

,/

/°

9t

-7

4 Sb2S3

25

Z TI2S

50

Fig. 3. Variation of log o180oc as a function of the TI2S c o n c e n t r a t i o n for the Sb 2 S 3 -T12 S glass system.

l Sb2S3

25

50

75

As2S3

Fig. 5. V a r i a t i o n of log o180oc , as a function of the As2S 3 c o n c e n t r a t i o n for the S b 2 S a - A s 2 S 3 - 0 . 2 TI2S glass system.

J. Olivier-Fourcadeet al. / Electrical and optiealproperties of chalcogenideglasses

280

Table 4 Position of room-temperature optical absorption edge Xg and corresponding energy Eg of Sb 28 3 -As 2S3 -T12 S glasses studied

v I,I,J

13 2

/ Sb2S 3

25

S0

7'5

AS2S 3

Fig. 6. Variation of the activation energy for electrical conduction E a as a function of the As2N 3 concentration in the Sb2S3-As 2$3 -0.2 T12S glass system.

generally decreases with increasing As2S 3. T h e v a r i a t i o n is n o t linear as shown in fig. 5. O n e can s u p p o s e that the r e p r e s e n t a t i v e curve m a y corres p o n d to the s u p e r p o s i t i o n of two lines of different slopes. T h e i n t e r s e c t i o n of the two lines occurs b e t w e e n the c o m p o s i t i o n 15 (0.5 Sb2S3-0.3 As2S3-0.2 T12S ) a n d 16 (0.35 Sb283-0.45 As2S 30.2 T12S) at 40 mol% of As2S 3. T h e e v o l u t i o n of the a c t i v a t i o n energy is likewise n o t c o n t i n u o u s as is shown in fig. 6. T h e a c t i v a t i o n energy of s a m p l e n u m b e r 15 (0.5 Sb2S3-0.3 A s 2 S 3 - 0 . 2 T12S) is characteristic of Sb2S3-T12S c o m p o s i t i o n s h a v i n g a T12S c o n c e n t r a t i o n less t h a n 20 mol%, as well as crystallized Sb2S 3 [7] a n d a m o r p h o u s As2S 3 phases. T h e activation energy rises a b r u p t l y for glass n u m b e r 13 (0.8 Sb2S3-0.2 T12S) a n d is of the o r d e r of 1.8 eV for the s a m p l e s c o n t a i n i n g m o r e

No.

Sb2S3-As2S3-T12S

Xg (/zm)

Eg (eV)

Eg/2

13 15 16 17 19

0.8-0-0.2 0.5-0.3-0.2 0.35-0.45-0.2 0.2-0.6-0.2 0-0.8-0.2

0.640 0.641 0.615 0.573 0.573

1.94 1.93 2.02 2.16 2.16

0.97 0.97 1.01 1.08 1.08

t h a n 60 tool% of A s 2 S 3. W e p o i n t o u t that the a c t i v a t i o n e n e r g y for s a m p l e s 19 (0.8 As2S3-0.2 T l z S ) a n d 13 (0.8 Sb2S3-0.2 T l z S ) is m u c h higher t h a n that of vitreous A s 2 S 3 r e p o r t e d in the literature: 1.02 eV [10] a n d 1.08 eV [11]. T h e same a c t i v a t i o n e n e r g y increase p h e n o m e n o n is o b served for the S b 2 S 3 - T l z S a n d As2S3-T12S b i n a r y systems c o n t a i n i n g 20 mol% of T12S.

4.2. Optical properties 4.2.1. Absorption edge T h e a b s o r p t i o n edge of the glasses b e l o n g i n g to the S b 2 S 3 - T l z S a n d S b z S 3 - A s z S 3 - T 1 2 S systems

2.25

2

1.75

E(eV)

T~ 50-

Table 3 Positions of room temperature optical absorption edge Xg and corresponding energy E~ of Sb2S3-T12S glasses studied No.

Sb2S3-T12S

Xg (/zm)

Eg (eV)

Eg/2

22 20 13 11 7 6 1

0.70-0.30 0.75-0.25 0.80-0.20 0.86-0.14 0.90-0.10 0.95-0.05 1 -0 a)

0.695 0.730 0.640 0.672 0.685 0.750 0.760

1.78 1.70 1.94 1.85 1.81 1.65 1.60

0.89 0.85 0.97 0.93 0.91 0.83 0.80

a) Crystalline.

5o0

soo

7o0

xtnm)

Fig. 7. Room temperature optical absorption edges of some glasses in the Sb2S3-TI2S system.

J. Olivier-Fourcade et al. / Electrical and optical properties of chalcogenide glasses 2.25

2

1.75

E(eV)

TZ

50-

01

500 0oo 700 (qm) Fig. 8. Room-temperature optical absorption edges of some glasses in the Sb2S3-As2S 3 -0.2 T12S system.

occurs in the visible spectral regions and ranges from 0.55 to 0.75/~m as shown in tables 3, 4, and figs. 7, 8 which show the absorption edge curves. =, % T I 2 5 0

20

0.75

40

60

80

~00

oTS;LL22

0,70

0,65

0.60

0.55

;

2o

,'o

~'o

8'o

,0o

°/o A s 2 S 3

Fig. 9. Evolution of the absorption edge as a function of substitutions.

281

The composition dependence of the absorption edge is presented in fig. 9 for glasses of the base system Sb2S3-T12S. The absorption edge decreases with increasing concentration of T12S up to 20 mol% where it reaches its minimum (0.64 /~m) and then increases with increasing concentration of T12S. The absorption edge of the glasses belonging to the Sb2S3 As2S3-0.2 T]2S section has a constant value between 0 and 36 mol% of As2S 3 until it reaches a minimum (0.57 t~m) at 60 mol% where it remains unchanged with As2S 3 content up to 80 mol%. Values of the optical gap determined from the spectral dependence of the absorption edge curves range from 1.6 to 1.94 eV for the base glasses Sb2S3-T12S and from 1.93 to 2.16 eV for the Sb2S3-As2S3-0.2 TlzS glasses. It appears that the optical gap increases with increasing content of As2S 3 and that these glasses ae wide gap materials. 4.2.2. Infrared transmission The infrared transmission spectra of the Sb2S3-As2S3-T12S system for specimens number 13, 16, 19 and 28 are shown in fig. 10. These glasses are transparent up to 11 /~m and their transmittance is 60-70%. They exhibit strong absorption bands at 2.9 and 6.3 /~m which result from traces of hydroxyl groups and water. These bands can be eliminated if care is taken during preparation and processing [12,13]. The wavelength cut-off of glass number 13 (0.8 Sb2S3-0.2 T12S) at 50% transmission occurs at 13.2/~m. The cut-off decreases slightly for glasses number 16 (0.35 Sb2S3-0.45 As2S3-0.2 T12S) and 19 (0.8 As2S3-0.2 T12S ), 11.39 and 12.85/~m respectively, and is considered to be due to As-S bonds. The transmission spectrum of glass number 28 (0.6 As 2$3-0.4 T12 S) indicates that increasing T12S content improves the transmittance. The absorption band at 6.3/~m due to water does not occur, but that at 2.9/~m is still present. The optical window of these chalcogenide glasses is limited by electronic absorption in the short-wavelength spectrum region and by phonon absorption in the long wavelength region. Table 5 summarizes the values of the edge absorption and the infrared cut-off of the glasses investigated. It

J. Olivier-Fourcade et a L / Electrical and optical properties of chalcogenide glasses

282

Table 5 Optical characteristics of some glasses in the Sb2S3-As2S3-TI2S system. No.

13 15 16 17 19 28

Composition

)~g a)

/~ IR

~kIR -- ~g

~]

F]

~k2

Sb2S3-As2S3-T12S

(ttm)

(ttm)

(/~m)

(~tm)

(/~m)

(~tm)

F2 (ttm)

0.8-0-0.2 0.5-0.3-0.2 0.35-0.45-0.2 0.2-0.6-0.2 0-0.8-0.2 0-0.6-0,4

0.640 0.650 0.620 0.580 0.580 0.72

13.30 11.46 11.39 11.36 12.85 11.49

12.66 10.81 10.77 10.78 11.27 10.77

2.94 2.94 2.94 2.94 2.94 2.98

0.31 0,25 0.261 0.31 0.30 0.30

6.37 6.30 6.29 6.23 6.25

0.12 0.13 0.12 0.25 0.21

a) Xg, optical absorption edge; Xm wavelength cut-off of the infrared transmission; X1 and X2, wavelengths of the "water band"; F 1 and F2, halfwidths of the "water band".

3

lOO

1__(ioJcm I

1

2

i

TYo

(a)

8O

GO

V 40

20

0

7

2,5

3

lOO

8

9

11 1315/k(lam

-~T('°3cm ')

,

2

TT,

(b)

8O

60

40

20

2,s

~

£5

i

s

6

7

8

9

.

~3

/~(I,ml

Fig. 10. Infrared transmission spectra of some glasses in the Sb2S3-As2S3-T12S system. (a) 0,8 Sb2S3-0.2 TI2S (13); (b) 0.35 Sb2S3-0.45 As2S3-0.2 T12S (16).

283

J. Olivier-Fourcade et al. / Electrical and optical properties of chalcogenide glasses

3

1oo

2

I i1o~cm ~ J

1

TTo

X

(c)

8O 10

40

20

2,5

i

3",5

i

3

5

6

7

8

9

2

11 13

X(am)

1

lOO

T'/.

(d)

°l

I0

Zt °

.i

Z,$

i,s

i

~

s

7

s 9

,1

13

X(lm)

Fig. 10. Infrared transmission spectra of some glasses in the Sb2S3-As2S3-TI2S system. (c) 0.8 As2S3-0.2 TI+S (19): (d) 0.6 As2S3-0.4 T12S (28).

appears from these data that As2S 3 a d d i t i o n decreases the wavelength cut-off from 13.3 to 11.36 /~m and the widest optical w i n d o w occurs in the 0.8 Sb2S3-0.2 T12S c o m p o s i t i o n (12.66/~m). T a b l e

6 gives a c o m p a r i s o n with other materials such as As2S 3, As2Se 3 a n d AszTe 3 glasses.

5. C o n c l u s i o n Table 6 Summary of activation energy and transmission range of glasses from arsenic chalcogenides

As2S3 As2Se3 As2Te3

Ea [ 1 4 ] (eV)

Transmission range [15] (~m)

1.02 0.98 0.43

1-11 1-15 2-20

All the chalcogenide glasses investigated are high-resistivity a n d wide-gap s e m i c o n d u c t o r s since their electrical c o n d u c t i v i t y ranges from 10 -6 to 10 -9 $2-1 cm -1 a n d their optical gap from 1.6 to 2.2 eV. I n the base glass system Sb2S3-T12S the electrical c o n d u c t i v i t y generally increases with increas-

284

J. Olivier-Fourcade et al. / Electrical and optical properties of chalcogenide glasses

ing T12S concentration. The variation of the activation energy suggests a change in the conduction mechanism. Substitution of antimony by arsenic strongly decreases the electrical conductivity and its activation energies implying different conduction mechanisms. The glasses have a wide optical window that is maximum (0.64-13.3 /~m) for the 0.8 SbzS3-0.2 TlzS composition. If antimony is replaced by arsenic, but cut-off wavelength decreases slightly.

References [1] A.M. Andriesh, J. Non-Cryst. Solids 77&78 (1985) 1219. [2] Z. Cimpl and F. Kosek, J. Non-Cryst. Solids 90 (1987) 577.

[3] A. Bouaza, J. Olivier-Fourcade, J.C. Jumas, M. Maurin and H. Dexpert, J. Chim. Phys. (1989) to be published. [4] A. Bouaza, A. Ibanez, J. Olivier-Fourcade, E. Philippot and M. Maurin, Mat. Res. Bull. 22 (1987) 973. [5] D. Ravaine and J.L. Souquet , J. Chem. Phys. 5 (1974) 693. [6] J. Olivier-Fourcade, J.C. Jumas, N. Rey, E. Philippot and M. Maurin, J. Sol. St. Chem. 59 (1985) 174. [7] J.C. Jumas, J. Olivier-Fourcade, N. Rey and E. Philippot, Rev. Chim. Min. 22 (1985) 651. [8] N. Rey, Thesis 3e cycle, Montpellier (1984). [9] J. Olivier-Fourcade, L. Izghouti, J.C. Jumas and E. Philippot, Rev. Chim. Min. 20 (1983) 385. [10] J.T. Edmond, J. Non-Cryst. Solids 1 (1968) 39. [11] R. Anderi Chin, P. Simidchieva and M. Nikiforova, C.R. Acad. Bulg. Sci. 18 (1965) 12. [12] S. Shibata, Y. Terunuma and T. Manabe, Mat. Res. Bull. 16 (1981) 703. [13] J.A. Savage and S. Nielsen, Phys. Chem. Glasses 6 (1965) 90. [14] J.T. Edmond, J. Non-Cryst. Solids 1 (1968) 39. [15] J.A. Savage and S. Nielsen, Infrared Phys. 5 (1965) 195.