Physica status solidi: Volume 7, Number 3 December 1 [Reprint 2021 ed.] 9783112497081, 9783112497074

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plrysica status solidi

V O L U M E 7 . N U M B E R 3 . 1964

Contents Review Article B . T . KOLOMIETS

Page Vitreous Semiconductors

(II)

713

Original Papers K . LÜCKE, H . PEELWITZ u n d W . PITSCH

Elektronenmikroskopische Bestimmung der Orientierungsverteilung der Kristallite in gewalztem K u p f e r

733

H . BLANK, P . DELAVIGNETTE, R . GEVERS, a n d S . AMELINCKX

A.

JANNUSSIS

Fault Structures in Wurtzite

747

Diamagnetismus von fast freien Elektronen mit Hilfe der Methode der Dichtematrix

765

V . O ALLINA a n d M . O M I N I

Vacancy as a Phonon Field Perturbation (V) B . H . K a m e e s 0 6 OCOßEHHOCTHX HAMARHHHEIMOCTH H BOCIIPHHMHHBOCTH raftaeHßeproBCKoro $eppoMarHeTHKa B TOHKe Kiopw . . . .

771 777

O. KANERT

Der Einfluß von Versetzungen auf die Intensität eines magnetischen Kernresonanzsignals

791

J . ARENDS

Color Centers in Additively Colored CaF 2 a n d BaF 2

805

R . LÜCK u n d T H . RICKER H . HEMSCHIK

Zur Änderung der T h e r m o k r a f t von Metallen im Magnetfeld. . .

817

Zur Theorie des Ferromagnetismus dünner Schichten

825

M . BOCEK, G . HÖTZSCH u n d B . SIMMEN

Die Temperaturabhängigkeit der Verfestigungskenngrößen von Magnesiumeinkristallen

833

P . JANSEN, W . HELFRICH u n d N . RIEHL

Die Wirkung von Licht auf raumladungsbeschränkte Defektelektronenströme in Anthrazen

851

Lichtempfindliche raumladungsbeschränkte Ströme

863

M. H Ö H N E

Versetzungen u n d Kernresonanz in AgBr

869

K.

HENNIG

Paramagnetische Resonanzuntersuchungen a n Fe-dotierten Silberhalogeniden

885

M.

STASIW

Zur Absorption von Silberbromid mit zweiwertigen Fremdionenzusätzen nach Bestrahlung (I)

893

W.

HELFRICH

H . LEINHOS

Reptation der Magnetisierungsschleife a n der Legierung E i s e n Kupfer 905

F . BROUERS e t J . DELTOUR

Séparation des modes collectifs et individuels dans u n gaz d'électrons (Continuai on cover three)

915

physica status solidi B o a r d of E d i t o r s P. A I G R A I N , Paris, S. A M E L I N C K X , Mol-Donk, W. D E K E Y S E R , Geni, W. F R A N Z , Münster, P. G Ö R L I C H , Jena, E. G R I L L O T , Paris, R. K A I S C H E W , Sofia, P. T. L A N D S B E R G , Cardiff, L. N É E L , Grenoble, A. P I E K A R A , Poznan, A. S E E G E R , Stuttgart, O. S T A S I W , Berlin, M. S T E E N B E C K , Jena, F. S T Ö C K M A N N , Karlsruhe, G. S Z I G E T I , Budapest, J . T A U C , Praha Editor-in-Chief P. G Ö R L I C H Advisory Board M. B A L K A N S K I , Paris, P. C. B A N B U R Y , Reading, M. B E R N A R D , Paris, W. B R A U E R , Berlin, W. C O C H R A N , Cambridge, R. C O E L H O , Fontenay-aux-Roses, H.-D. D I E T Z E , Aachen, J . D. E S H E L B Y , Birmingham, G. J A C O B S , Gent, J . J A U M A N N , Köln, E. K L I E R , Praha, E. K R O E N E R , Clausthal-Zellerfeld, M. M A T Y A S , Praha, H. D. M E G A W , Cambridge, T. S. M O S S , Camberley, E. N A G Y , Budapest, E. A. N I E K I S C H , Jülich, L. P A L , Budapest, M. R O D O T , Bellevue/Seine, B. V. R O L L I N , Oxford, H. M. R O S E N B E R G , Oxford, R. Y A U T I E R , Bellevue/Seine

Volume 7 • Number 3 • Pages 711 to 1058 and K 141 to K 204 December 1, 1964

A K A D E M I E - V E R L A G .

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LIN

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UND

W I S S E N , E r i c h B i e b e r , 7 S t u t t g a r t S . W i l h e l m s t r . 4 — 6 or t o D e u t s c h e B u c h - E x p o r t u n d - I m p o r t G m b H , L e i p z i g C 1, P o s t s c h l i e ß f a c h 276

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Schriftleiter und verantwortlich für den Inhalt: Professor Dr. Dr. h. c. P. G ö r l i c h , Berlin C 2, Neue Schönhauser Str. 20 bzw. Jena, Humboldtstr. 26. Redaktionskollegium: Dr. S. O b e r l ä n d e r , Dr. E. G u t s c h e , Dr. Vt. B o r c h a r d t . Anschrift der Schriftleitung: Berlin C 2, Neue Schönhauser Str. 20, Fernruf: 426788. Verlag: Akademie-Verlag GmbH, Berlin \V 8, Leipziger Str. 3 - 4 , Fernruf: 220441, Telex-Nr. 011773, Postscheckkonto: Berlin 35021. Die Zeitschrift „physica Status solidi*' erscheint jeweils am 1. des Monats. Bezugspreis eines Bandes MDN 60,-. Bestellnummer dieses Bandes 1068/7. Gesamtherstellung: V E B Druckerei „Thomas Müntzer" Bad Langensalza. — Veröffentlicht unter der Lizenznummer 1310 des Presseamtes beim Vorsitzenden des Ministerrates der Deutschen Demokratischen Republik.

Review

Article

phys. s t a t . sol. 7, 713 (1964) A. F. Joffe Physical Technical Institute, Academy oj Sciences of the USSR,

Leningrad,

Vitreous Semiconductors (II) *) By B . T . KOLOMIETS Contents 1.

Introduction

2. Region

of glass

formation

3. Physicochemical properties of chalcogenide 3.1 Density 3.2 Structure 3.3 Viscosity 3.4 Softening temperature 3.5 Microhardness 3.6 Coefficient of linear expansion 3.7 Chemical durability 3.8 Stability 4. Optical properties of chalcogenide glasses

glasses

5. Electrical properties 5.1 Conductivity 5.2 Sign of current carriers and of thermal e.m.f. 5.3 Dependence of conductivity on composition 5.4 Conductivity and impurities 5.5 Concentration and mobility of current carriers 5.6 Temperature dependence 5.7 Dielectric constant 5.8 Effect of gamma radiation 6. Photoelectric properties 6.1 Photoconductivity 6.2 P h o t o - e . m . f . 7. Change of properties 8. Oxychalcogenide

during

the glass-crystal

transition

glasses

References 4. Optical Properties of Chalcogenide Glasses

First data on the character of the absorption and transmission spectra in the group of non-oxide glasses appeared in 1950 to 1953 in the articles of FRERICHS who has described the optical properties as As2S3 and indicated their possible applications [52], Later a number of publications appeared in which were discussed optical properties of both As2S3 and As2Se3, As2Te3) and some others as well [19, 20, 33, 51]. P a r t I see phys. stat. sol. 7, 359 (1964). 47*

714

B . T . KOLOMIETS Fig. 7. Optical absorption spectrum in sulphide glasses: 1: AsjS,; 2 : AS 2 S 3 -T1 2 S; 3 : As 2 S 3 -8 As2TCS; 4: 2 As 2 S 3 • Sb 2 S B

Fig. 8. Optical absorption spectrum in selenidc glasses. 1: As 2 Se 8 ; 2 : 2 As 2 Sc 3 -As 2 Te 3 : 3: As 2 Se 3 • Tl 2 Se; 4: 5 As 3 Se 3 • Sb 2 Se 3 ; 5 : Tl 2 (Se 0 . t Tei,. 5 ) • As 2 Te 3

0 ASiSj As2Se3

20

40 60 composit/on(%)—»- As2Se3 As2Tej

15 12 Wavelength (jim)-

Fig. 9. The shift of the optical absorption edge caused by variations in composition in the system As 2 Se 3 -As 2 Se 3 (2) and As 2 Se 3 -As 2 Te 3 (1)

Following the discovery of the vitreous state in the alloys of these chalcogenides with the chalcogenides of a number of metals, we have started a systematic study of their optical properties. These studies were performed on polished disk-shaped specimens using a model HKC-14 spectrophotometer. The most complete information on the character of the absorption and transmission spectra is available at present for the group of glasses presented in Fig. 1. A characteristic feature for all the compositions is the existence of a broad transmission region in the infrared, as well as the presence of only a small number of absorption bands. The position of the optical absorption edge and of individual absorption bands can undergo considerable variations depending upon the composition. This is illustrated by Fig. 7, 8, and 9 where are presented data obtained for some sulphide and selenide glasses in the wavelength region extending up to 18 fim. VASHKO et al. have published results of the absorption spectra on the system As2S3-As2Se3 at wavelengths up to 25 ¡im [20].

Vitreous Semiconductora (II)

715

The nature of the absorption bands presents an interesting problem. Experimental evidence in this field is very scarse. However already first studies have shown t h a t some of the absorption bands are of the impurity nature. For instance, a strong absorption band in As 2 Se 3 and its alloys with As 2 S 3 at 12.6 [im is apparently due to the presence of As 2 0 3 formed in the course of preparation in the reaction with oxygen dissolved in selenium and liberated from the tube walls. This is confirmed by the absence of this particular absorption band in the material prepared in a thoroughly outgassed tube from oxygen-free selenium. Chalcogenide glasses are fairly transparent in the transmission region. I t may be said for illustration that glass plates 0.3 mm thick prepared without the application of methods used in optical glass founding and of special surface treatments transmit up to 60 to 80% of the radiation. The coefficient of absorption for the glass Tl 2 Se • As2Se3, according to preliminary information, is 1.6 cm - 1 . The refractive index calculated from the data obtained in the measurements of the dielectric constant for the system As 2 Se 3 -As 2 Te 3 ranges from 3.5 to 4.5, depending on the actual composition. The introduction of germanium and iodine into arsenic selenide does not, to any appreciable degree, affect the character of the optical absorption. The investigation of the temperature dependence of the optical absorption edge has shown t h a t within the range + 1 0 0 to —100 °C the temperature coefficient of the shift for chalcogenide glasses does not practically differ from t h a t for crystal semiconductors. For As 2 Se 3 it is equal, approximately, to 1.5 x l O - 4 , and for TI2Se • As 2 Te 3 it is about 12 x 10"4 [xm/deg. 5. Electrical Properties 5.1

Conductivity

I t has been established in the course of studying the electrical properties of chalcogenide glasses that their conductivities range from 10 - 1 2 to 10~3 Q" 1 cm - 1 . The magnitude of the conductivity depends on composition generally in such a way that the heavier the atoms forming a part of the glass, the higher its conductivity. I n Table 8 are presented the magnitudes of the conductivity for several systems revealing an appreciable electric conductivity. Table 8 Conductivity of chalcogenide glasses of different compositions Systems As2Se3-As2S3 As 2 Se 3 -As 2 Te 3 As 2 Se 3 -Sb 2 Se 3 As 2 Se 3 -Tl £ Se Tl 2 Se • As 2 (Se, Te) 3

Glass conductivity range (CI-1 cm" 1 ) 10' 1 3 10' 1 3 10' 1 3 10' 1 3 lO' 7

to to to to to

lO" 14 10"« 10- 10 10" 7 10" 3

The investigation of electrical properties of glasses represents already for a long time one of the most important aspects of research of the vitreous state. The high conductivity of chalcogenide glasses provides new possibilities for studies in this direction. However before starting such an investigation one has to obtain information on the mechanism of conduction. I t is known that the relatively high

716

B . T . KOLOMIETS

conductivity of oxide glasses is associated to a considerable degree with the ionic mechanism of conduction. To reveal ionic conduction in glasses described here, experiments were carried out based on the well-known method of T U B A N D T . As the object for the study were taken materials from the system As2Se3-As2Te3. These experiments which were performed also at high temperatures, close to the softening temperature, did not reveal any traces of the transport of material. Thus this experimental evidence proves that in the chalcogenide glasses investigated we deal with an electronic mechanism of conduction. Another fact speaking in favour of this conclusion is the existence of photoconductivity and Hall e.m.f. both in the above and in all the other systems of vitreous chalcogenides. 5.2 Sign

of current

carriers

and of thermal

e.m.f.

The sign of current carriers as determined from the sign of the thermal and photoelectric e.m.f.'s corresponds to hole conduction in all chalcogenide glasses, without exception. The magnitude of the thermal e.m.f. in chalcogenide vitreous semiconductors is fairly large and depends on composition. This may be illustrated by the graphical data of Fig. 10 corresponding to one of the most thoroughly investigated glassy systems, viz. As 2 Se 3 -As 2 Te 3 [2]. The thermal e.m.f. for this system increases exponentially with the decrease of temperature. Fig. 10. The relation of the thermal e.m.f. vs. composition in of the system As 2 Se 3 -As^Te 3

As2Te3(%)-

o-

IÌ

a

'

i , itr

XT'

ZO

40

60 80 As2Te3(%)-

Fig. 11. The relation of conductivity vs. composition for substances in the system As 2 Se 3 -As 2 Te a 1 : for vitreous materials 2 : for crystalline materials

40

60 00 Te-content (%)-

Fig. 12. The relation of the conductivity of g ses vs. composition in the system Tl a Se • As a (Se, Te) a

717

Vitreous Semiconductors ( I I )

5.3 Dependence

of conductivity

on

composition

The investigation shows that in general the conductivity increases with the increase of the content of heavy components in a glass. Next, within each system the conductivity changes monotonically with composition between the values corresponding to the individual components as this is shown in Fig. 11 for the system As2Se3-As2Te3, and in Pig. 12 for the case of the system TlaSe • As2(Se, Te)3. I t is seen from the latter that in this system the conductivity of chalcogenide glasses attain such a high value as 10~3 Q" 1 c m - 1 which is two orders of magnitude higher than the conductivity of one of the classical crystal semiconductors — selenium. 5.4 Conductivity

and

impurities

The investigation of the role of impurities in chalcogenide glasses was carried out in several directions. One of them consisted in studying the variation of the conductivity as a function of composition by varying properly the proportions between the compounds. As the first object of such an investigation served TISe • As2Se3 [7]. Preliminary studies carried out on both this material and others have shown that, in contrast to crystal semiconductors, a small deviation from the original composition (of up to 1 to 3%) does not cause any appreciable change of their properties. Deviations from the compositions within + 10 to 30% result in conductivity changes by 1 to 4 orders of magnitude. It has been established that an increase in the content of arsenic and selenium causes a decrease, and that of thallium — an increase of the conductivity. In Fig. 13 is shown the dependence of the conductivity of the glass TISe • As2Se3 on thallium content. In contrast to the case where the selenium content is varied, the conductivity here changes monotonically within the total range of thallium concentration variation from +28.6 to —9.6at.%, the absolute magnitude of the conductivity exhibiting an increase by a factor of about 10000. A still further increase in the thallium content results in the formation of crystal substances which are not transformed into glasses even by quenching, that is, by a rapid cooling. The removal of thallium leaves the substance in the vitreous state. The dependence of the conductivity on the arsenic content is similar to the one presented graphically in Fig. 13. Within the arsenic concentration variation range of 28.6 to —23.9 at.% the conductivity increases by approximately a factor of 1000. These data show that one can change the conductivity of chalcogenide glasses within a fairly wide range. 2.0

10'

1.6

2 o

""" o 0.8 |

1A Fig. 13. The relation of conductivity (1) and activation energy of current carriers (2) vs. variation in thallium content in the glass TLSe • As,Se s

0.4

F *i0

SO

20

10

0

-10

-20

Variation in thallium content(%)~

718

B . T . KOLOMIETS

The investigation of the temperature dependence of the conductivity in glassy semiconductors did not reveal any break in temperature characteristics which represents a typical feature of the impurity conduction in crystal semiconductors. The second direction of research is associated with the study of the role played by foreign impurities [7,11, 16J. As an object for the study were taken the glasses As2Se3 and Tl2Se • As2Se3, into which germanium and iodine were introduced as impurities. A typical feature for both cases is the resulting decrease of the conductivity. However in the glass of a more complex composition such a decrease is less pronounced, in other words, a conductivity change equal to that of the case with As2Se3 is attained here at considerably higher concentrations of the impurity. Besides, in the case of arsenic selenide a typical feature is an appreciable increase of the conductivity at low concentrations of the iodine impurity. The dependence of the conductivity of Tl2Se • As2Se3 on the content of iodine and germanium is presented graphically in Fig. 6. For As2Se3 we have a similar picture except for the above mentioned increase of the conductivity at low concentrations of iodine. The investigation of the temperature dependence of the conductivity in these materials also did not reveal any indications of impurity conduction. The results of these and other investigations have brought us to the conclusion that the effect of impurities on the conductivity of glassy semiconductors is small as compared with the case of crystal semiconductors. To confirm this hypothesis, a zone refining of one the most readily crystallizing glasses, viz. As2Se3 • 2 As2Te3, was carried out, and the conductivity and the sign of current carriers both before and after the refining were determined in the vitreous and crystalline states. The preliminary results of such experiments are presented in Table 9. As seen from the Table, the refining of the material is accompanied by a decrease of the conductivity in the crystal state by more than two orders of magnitude and by the transition from hole to electron conduction, whereas the conductivity of the glass practically does not change and the conduction remains to be of the p-type. Table 9 Effect of impurities on glass and crystal conductivity Crystal Material

Type of conduction

O" (Î2- cm" 1 )

Type of conduction

n (cm - 3 )

(cm2/Vs)

60

_

_

P

1 X IO" 6

P

4 x 10"2

1016

15

n

0.9 X 10-6

P

(H"1 As2SeTe2 before zone refining As2SeTe2 after zone refining

Glass

a cm- 1 )

1

This experiment represents one more proof of the fact that small concentrations of impurities which can drastically change the properties of the most of crystal semiconductors do not practically affect the conductivity of the vitreous semiconductors. This is in agreement with general theoretical considerations on the role of impurities in vitreous substances [44,46,47,48],

719

Vitreous Semiconductors (II) 5.5 Concentration

and mobility of current

carriers

The electrical properties of vitreous chalcogenide semidonductors may be considered at present as fairly well known, at any rate in general outline. However such fundamental parameters as concentration and mobility of current carriers remain unstudied. The absence of these data is associated with serious difficulties encountered in measurements of the Hall effect in semiconductors with an amorphous structure because of a high resistance and a low value of the current carrier mobility. Bslow are presented preliminary results of investigation of the Hall effect in vitreous semiconductors. The investigation was carried out on materials of the system Tl 2 Se • As2(Se, Te) 3 which is notable among the other previously investigated systems for its high electric conductivity [8]. Depending upon the content of Te, its conductivity may vary from 10~7 to 10" 3 Q" 1 cm - 1 . Measurements were done on the type HHX-1 instrument (which is a Hall potential meter). The principle underlying its operation consists in using the wellknown method of measurement of the Hall effect in an alternating magnetic and electric field. The instrument permits to perform Hall effect measurements on materials with electric conductivities of 10" 1 to 10~5 cm - 1 . The range of Hall voltages measured extends from 0.2 to 3000 jxV (eff.). The maximum magnetic field strength in the measurements reached 1800 G. The specimens to be studied were cut out of ingots and represented rectangular parallelepipeds measuring 12 x 4 x 1.5 mm 3 . A reliable electric contact was ensured by fusing platinum wire of diameter 0.1 mm into the specimens. At room temperature the Hall effect was measured in three compositions of the lowest resistance in this system. Data on concentration and mobility of the current carriers for other compositions at room temperature have been obtained by extrapolating the measurements of the temperature dependence of the Hall effect. In Fig. 14 are presented the final results of these measurements from which it is seen that the concentration of current carriers increases with the increase of the tellurium content monotonically from 5 X10 1 1 to 6 X10 1 8 cm" 3 , the concentration relationship following that of the conductivity. The data of Fig. 14 correspond to

720

B . T . KOLOMIETS

room temperature. The conductivity values have been obtained by direct measurements. The mobility of current carriers calculated as the product of the Hall constant times conductivity does not practically change with composition and by the order of magnitude is somewhat above 10 ~2 cm2/Vs. Measurements of the temperature dependence of the Hall effect have shown a weak dependence of the mobility on temperature. One should be careful in applying the term "mobility of current carriers" to vitreous semiconductors since the question on the mechanism of conduction in them remains open. According to some experimental data supported by theoretical considerations there is no impurity conduction in glasses. If we assume the conduction of glasses to be similar to the intrinsic conduction in crystal semiconductors, then the "mobility" obtained from the Hall effect will yield the difference in mobilities. I t is interesting to note in this connection that one obtains different signs for current carriers in materials of the system investigated depending on whether the thermal e.m.f. or the Hall effect techniques are used for the determination. The sign of the thermal e.m.f. indicates p-type conduction whereas the sign of the Hall effect speaks in favour of conduction of the n-type. I t follows from these data that the variation of conductivity with composition in vitreous semiconductors of the system Tl2Se • As2(Se, Te) 3 is caused by the variation in the concentration of current carriers, and their mobility is very small. One may expect that this will be true also for other vitreous semiconducting systems. One of the compositions of this systems, viz. Tl2Se • As2Te3, was subjected to a more detailed study which has brought us to the conclusion that the mobility of holes in this material is one order of magnitude higher than the electron mobility, and that the hole mass exceeds the mass of a free electron by a factor of 30 [18]. Besides, the drift mobility was investigated using the Spear technique [9]. The current carriers were identified as holes which is in agreement with the sign determined from the thermal e.m.f. Trapping centers for both electrons and holes have been found, the efficiency of trapping for the two types of carriers being approximately equal. 5.6 Temperature

dependence

The temperature dependence of conductivity was investigated almost for all above mentioned vitreous materials within the range from the room to softening temperature, and in some cases up to 300 to 500 °C above the latter. I t has been found that in all cases without a single exception the temperature dependence of the conductivity obeys an exponential law common for semiconductors. A characteristic feature is the presence of one slope which does not change after transition into the liquid state [10]. This speaks in favour of the absence of the impurity conduction. The temperature dependence of conductivity within the temperature range specified above for vitreous semiconductors of several different compositions in the system As2Se3-As2Te3 is given in graphical form in Fig. 15. A similar dependence has been found for all the glasses investigated by us. The experimental data presented in this chapter as well as those obtained in the course of studying the photoconductivity, which will be discussed later, indicated that the glasses described here represent typical semiconductors, their distinctive feature being the absence of impurity conduction. The absence of the long-range

721

Vitreous Semiconductors (II) Fig. 15. The temperature dependence of conductivity of vitreous materials in the system As 2 Se 8 -As 2 Te s at the transition from the solid to the liquid state 1: 4 As 2 Se 8 • As 2 Te 3 ; 2 3 As 2 Se, • As 2 Te 8 ; 3 : 2 As 2 Se, • As 2 Te 9

1.5

2.0

2.5

3.0

f

order and the fact that the glass retains all characteristic semiconducting properties may be considered as a cogent argument for the determining role of the short-range order in the electrical properties of substances. 5.7 Dielectric

constant

The dielectric constant has been measured only for the system As2Se3-As2Te3 out of the vast number of chalcogenide glasses. The corresponding data are presented in Table 10 together with the values for the amorphous vitreous selenium. Table 10 Dielectric constant of glasses in the system As2Se3-As2Te; Composition Se As2Se3 4 As2Se3 • 3 As2Se3 • AsgSc^ • 2 As2Se3 • As2Se3 •

As2Te3 As2Te3 AsgTc^ 3 As2Te3 2 As2Te3

Resistivity Q (fi x cm) ~ ~ 3.6 1.1 1.8 3.3 1.0

10 ls 10 13 x 109 x 10® x 107 x 10« x 106

5.8 Effect of gamma

Dielectric constant E (CGS)

Refractive index

7.20 12.25 14.10 14.90 17.7 18.7 20

2.69 3.50 3.76 3.87 4.22 4.34 4.48

n

radiation

Bobkova and Lobanov [41] investigated the variation of the electric conductivity in a number of glassy semiconductors caused by gamma irradiation at integral doses of up to 109 roentgens. They have succeeded in establishing that the conductivity is a complicated function of irradiation dose. At first it increases, then passes through a maximum at a dose of (2 to 3) x 10s roentgens, decreases below the original level and finally increases again tending to saturation. Annealing the specimen after gamma irradiation results in an increase of its conductivity.

722

B . T . KOLOMIETS

6. Photoelectric Properties 6.1

Photoconductivity

All chalcogenide glasses posses an intrinsic photoeffect characterized by a time constant common for the main number of the investigated semiconductors, which serves as one of the proofs of the electron conduction in them. In all cases without a single exception the sign of current carriers as determined by the capacitor technique was found to be positive. The investigation of the spectral response of the intrinsic photoeffect carried out with light modulated at 300 to 400 Hz with subsequent amplification has shown that typical for this class of substances is a broad sensitivity region and its dependence on composition. This is illustrated in Fig. 16 by spectral response curves for the glasses of different composition, and in Fig. 17 by the dependence of the spectral sensitivity on the variation of composition within one system. Approximately the same holds for other compositions, some of them being presented in Fig. 1. The investigation of the effect of foreign impurities on the spectral response of the intrinsic photoeffect was carried out on the glass TlAsSe 2 [16]. It has been shown that the introduction of iodine and germanium shifts the sensitivity into the short-wavelength region of the spectrum. In germanium, for instance, the peak of the photocurrent can be shifted from 0.9 to 0.5 pim. The authors associate this phenomenon with the strengthening of covalent bonds inside the chains forming the structure of the compound under investigation. Fig. 16. The spectral response of the intrinsic photoeffect in vitreous materials of different composition 1 As 2 Se 3 ; 2 . 3 As 2 Se 3 • As 2 Te 3 , 3 As 2 Sc 3 • TI 2 Se

Wavelength

(jim)-

100

80 60

y/ 11 2*

//

%o

^ I 400

J

/

600

\

3

\

/

\

\

Y

800

WOO

1200 1W0 Wavelength (nm)

1600

Fig. 17 The variation of t h e spectral response of the intrinsic photoeffect with changes in composition for vitreous materials in the system As 2 Se a -As 2 Te 3 1 As 2 Se 3 , 2 3 As 2 Se 3 -A3 2 Te a , 3 As 2 Se 3 -As 2 Te a ; 4 As,Se 3 • 3 As 2 Te 3

723

Vitreous Semiconductors (II)

The change of resistance with illumination is fairly large in some chalcogenide glasses, in particular in arsenic selenide it exceeds that of Sb2S3 used in vidicons. This interesting phenomenon has attracted the attention of a number of investigators. LYUBIN [13,14] carried out a detailed study of the intrinsic photoeffect in thin films of arsenic selenide (As2Se3). (It should be noted that up to now we have been describing the bulk properties of materials). Investigated were films 0.5 to 2 ¡j,m thick deposited in vacuum on substrates of polished glass coated preliminarily by a semi-transparent film of Pt, Au, Al, or Sn0 2 . To permit measurements "along" the semiconducting film, a gap 50 to 100 [im wide was provided in the conducting coating. Semitransparent electrodes of Al, Au or Ag were deposited in vacuum over the film thus enabling studies "across" the film to be carried out. In some cases upper electrodes were not deposited, and measurements were performed by electron beam contact. The resistance of such films changed by a factor of 200 to 400 at illumination intensities of about 100 lx. At transverse measurements a photo-e.m.f. of 0.4 V was observed. Illuminating a specimen with chopped light has shown that the rise and decay times of the photocurrent do not exceed 10"3 s. The investigation of the spectral response of the intrinsic photoeffect has revealed that at transverse measurements the shape of the response curve depends strongly on the polarity of the potential applied. If, for instance, the illuminated electrode is at a positive potential, the peak of the photocurrent lies in the ultraviolet region of the spectrum. Reversing the polarity of the potential shifts the peak of the photocurrent into the visible region. The magnitude of the applied potential did not affect in any case the shape of the spectral response of the intrinsic photoeffect. The sign of the photo-e.m.f. in some specimens was found to be dependent on the wavelength of the incident radiation. If, for instance, the upper electrode is illuminated with short-wavelength light, it becomes negatively charged; illumination with long-wavelength light causes it to charge positively. These peculiarities of the intrinsic photoeffect in films of As2Se3 are illustrated by curves in Fig. 18. Measurements of the temperature dependence of conductivity carried out in the longitudinal direction revealed an ordinary exponential law yielding for the activation energy of current carriers a value of 1.7 eV. The situation is different with the photoconductivity. In the low temperature region we have also an exponential increase corresponding to an average activation energy of 0.5 eV. However at temperatures at which the value of the photoconductivity becomes approximately equal to the dark conductivity, the dependence reverses its sign.

Fig. 18. The spectral response of the photoeffect photocurrent across the film at a positive potential at the illuminated electrode 2 photocurrent across the film at a negative potential at the illuminated electrode 3 • photocurrent along the film 4 negative photo-e.m.f. 5 positive photo-e.m.f. 1

350

400 450 500 550 600 650 \(nm}—

724

B . T. KOLOMIETS Fig. 19. The relation of activation energy vs. composition of glasses in the system As 2 Se 3 -As 2 Te 3 calculated from: 1 : temperature dependence of conductivity 2 : photoconductivity ¿max/ 2 3 : optical absorption edge

0

20

40

60 80 As2Te3(%)

WO »

The exponential increase of the photocurrent may be explained if one accepts the mechanism of trapping of illumination-excited current carriers, in other words, if one assumes the presence of local trapping levels in the forbidden band, their depth in this particular case being 0.5 eV. The important conclusion of the above investigation consists in that the investigation of the temperature dependence of photocurrent may become a simple method to determine the location of the trapping levels in amorphous photoconducting films. It is interesting to note that several years later the existence of trapping centers in the forbidden band of vitreous semiconductors has been proved experimentally by A N D R I Y E S H who has found the depth of these centers in the glass Tl a Se • As 2 Te 3 to be 0.3 eV using the method of thermostimulated current [17]. The photoconductivity, the edge of optical absorption, and the temperature dependence of conductivity were used to calculate the activation energy of current carriers in vitreous chalcogenide semiconductors and its dependence on variations in composition [2, 10, 19]. The corresponding data for one of the investigated systems, As2Se3-As2Te3, are presented in Fig. 19. The characteristic point here is that the activation energy as determined from the temperature dependence of conductivity is higher than that obtained from optical and photoelectric data. It is well known that for crystal semiconductors the reverse is true. 6.2

Photo-e.m.f.

Besides the experimental results on the photo-e.m.f. in films of arsenic selenide described above, A N D R E Y C H I N [15] who studied the electrical and photoelectrical properties of vitreous semiconductors in the systems As 2 S 3 -As 2 Se 3 and As2Se3-As2Te3 has established the existence of photo-e.m.f.'s reaching, in the case of As 2 S 3 a value as high as 1V. It was interesting to study the dependence of this photo-e.m.f. on composition in the above mentioned systems. For this purpose a number of alloys has been prepared in which selenium and tellurium were gradually substituted for sulphur. The experimental specimens represented plates 0.5 to 2 mm thick having areas 3 to 5 X10 to 15 mm 2 cut out of ingots, on whose surface aluminium and gold electrodes were deposited in vacuum. The separation between the electrodes was 0.5 mm. In the majority of cases four electrodes, two of them gold and two — aluminium ones, were deposited on a specimen thus permitting to perform checking measurements. The illumination was uniform over the surface of a specimen and was maintained at 10000 lx in all cases. The photo-e.m.f.

Vitreous Semiconductors (II)

725

were measured with a quadrant electrometer with a sensitivity of 120 divisions per 1 V. Illuminating a section with different electrodes (gold-aluminium) produced an e.m.f., aluminium always acquiring a negative potential, and gold—a positive one. The illumination of sections with identical electrodes never resulted in any appreciable e.m.f. The results of this preliminary investigation are given in Fig. 20. I t is seen t h a t the magnitude of the e.m.f. is connected with composition in such a way t h a t substituting selenium and tellurium for sulphur results in its gradual decrease. The nature of the photo-e.m.f. observed remains an interesting problem. One may make two suggestions, the first of them based on the existence of the contact potential difference, and the second — on the presence of a barrier layer at t h e metal-semiconductor interface. The experimental evidence is not yet conclusive enough to make either of these points of view preferable. However it seems to us that under the specified experimental conditions, i.e. at high illumination intensities, when in rectifier photocells saturation is achieved and there is no more difference between a "good" and a " b a d " barrier layer, there should not be such a large spread in experimental data. On the other hand, such a spread becomes only natural if we take into account a marked dependence of the contact potential on the condition of t h e surface, on the details of electrode deposition, and so on. 7. Change of Properties During the Glass-Crystal Transition I n contrast to oxide glasses, chalcogenide glasses crystallize much more readily. For some compositions taken at the softening temperature, for instance, the crystallization becomes completed at the end of two to three hours. This feature permits to follow the change in the properties of a substance going over from the vitreous into the crystal state. Fig. 11 illustrates the corresponding change of conductivity. I t is seen t h a t the conductivity of a composition corresponding to the central point in the system .Asg Se3- AsgTc g is 10 8 £2 1 cm 1 when in the vitreous state, and 102 i2 _ 1 cm' 1 — when in the crystal state. The glass-crystal transition in materials of a complex composition results in a change of other properties as well, such as the magnitude and sign of the photoeffect, the sign and magnitude of the current carrier mobility, etc.

Fig. 20. The relation of the photo-e.m.f. in chaJcogenides of arsenic vs. composition

726

B . T . KOLOMTETS Fig. 21. The spectral response of the intrinsic photoeffect of the glass 4 As,Se, • As z Te 3 in the solid (1) and liquid (2) states

1000 1200 Wavelength (nm) —»-

Large variations of the conductivity in crystal semiconductors transferred into the liquid state by melting were observed on quite a number of materials. It has been also established that after the transition to the liquid state the coordination number of germanium changes from 4 to 8, and that of indium antimonide — from 4 to 6. Having this in mind one might have suggested that the above mentioned change of conductivity by 10 orders of magnitude might be due to a change in the short-range order when going over from the vitreous into the crystal state. For this purpose an investigation was undertaken in order to study the temperature dependence of the conductivity and photoconductivity of vitreous semiconductors in the system As2Se3-As2Te3 within a broad temperature range [2,10,12], The study of the conductivity within the temperature range extending from room temperature to temperatures 200 to 500 °C above those at which softening occurs has shown that in all cases an ordinary exponential law is obeyed without any changes in the slope of the temperature characteristics. These results are illustrated in part by Fig. 15. The absence of any changes in the behaviour of the conductivity enables one to suggest that no essential changes in the short-range order take place during crystallization carried out below the softening temperature. The intrinsic photoeffect is a structure-sensitive characteristic of semiconductors. Therefore to check the above point of view, an investigation has been undertaken of the spectral response of the intrinsic photoeffect at room temperature and in the liquid state (that is, in the melt) above the softening temperature [12]. The results of this investigation which may be considered as original, since the spectral sensitivity in the melt was measured here for the first time, are presented in Fig. 21. The shift of the spectral sensitivity curves seen in the graph is not important and lies within the range determined by the temperature dependence of the energy gap, which is confirmed by measurements of the temperature dependence of the optical absorption edge position. The absence of any changes in the conductivity and photoconductivity at elevated temperatures, 200 to 500 °C above the softening temperature, indicates the existence of strong covalent bonds in the structure of the short-range order in the glasses investigated. That is why a change in the short-range order during crystallization or vitrification seems to be unlikely. Therefore we ha veto accept that the observed change of conductivity by a factor of 10 10 is due to some other reasons. The reasons are apparently the different role of impurities in glass and crystal and

727

Vitreous Semiconductors (II)

difference in the long-range order determining the mobility of the current carriers. These considerations are confirmed by the experimental data presented in Table 9. The complexity of the compositions studied (the presence of many components) naturally makes the interpretation of experimental data a difficult task. Therefore attempts were made to measure the conductivity and photoconductivity on substances of a simpler composition, in particular on arsenic selenide prepared from spectroscopically pure elemental constituents. The investigation was carried out in such a way that following the glass preparation one half of the ingot was transferred into the crystal state, and specimens were cut out of both parts to measure the conductivity and its temperature dependence. The spectral response of the intrinsic photoeffect was studied on freshlycleaved surfaces. Already the first experiments yielded interesting results. Measurements of the electrical conductivity, for instance, have shown that the conductivity of crystalline arsenic selenide, in contrast to the previously described materials, not only differs very little from t h a t i n t h e vitreous state, but is even somewhat lower than that [11]. In Fig. 22 is shown the temperature dependence of the conductivity for arsenic selenide in two states of aggregation. Within the total temperature range investigated the crystal material does not have a region of impurity conduction in contrast to crystal substances investigated earlier, and it is seen from the slope of the characteristics that the activation energy of current carriers in the crystallized arsenic selenide is somewhat higher. Fig. 22. The temperature dependence of the conductivity of arsenic selenide 1: vitreous state 2: crystal state

\\ V

Fig. 23. The spectral response of the intrinsic photoeffect of arsenic selenide 1: crystal state 2: vitreous state

V \

\

°\ A

-10

-12

2.0

3.0

25 JOl

T 48

physica

\

\

-n

V 35

OS

1.0

Waveiength(jun)-

728

B . T . KOLOMIETS

Fig. 23 illustrates the spectral response of the intrinsic photoeffect in both vitreous and crystal As 2 Se 3 . I t is seen that the curves are similar to each other and differ only in that the sensitivity region in the vitreous material is somewhat wider. From the data presented in Fig. 22 and 23 activation energies have been calculated, which are given in Table 11 together with the value of conductivity. These data seem to us to be one more conclusive proof of the above suggestion that the short-range order in the investigated system of glasses does not undergo any essential changes during the transition from the vitreous into the crystalline state. The Table reveals one more interesting result. The transition from crystal to glass results in a decrease of the energy gap by about 0.1 eV. This change is in agreement with theoretical considerations and calculations of G U B A N O V [ 4 5 ] . Moreover, if we assume that the mobility of current carriers and their effective masses are the same in the vitreous and crystal states, it is easy to calculate that a change of the energy gap of 0.1 eV should result in a conductivity change by one order of magnitude. As follows from Table 11, it is exactly within this range that the conductivity of arsenic selenide changes. Table 11 Parameters of arsenic selenide in vitreous and crystal states Material As2Se3 crystal state As2Se3 vitreous state

Conductivity (H- 1 cm- 1 )

(2 to 4) x 10- 13 (10 to 20) X 10- 13

Activation energy (eV) from a = a(T)

,

from

2.1 2.0

¿max

1.7 1.6

¿1

from optical absorption edge

1.5

8. Oxychalcogenide Glasses There is an interesting question concerning the possibility of obtaining compound oxychalcogenide glasses [56]. An attempt to use the well-known criteria of glass formation formulated by Z A C H A R I A S E N and W I N T E R - K L E I N did not lead to positive results, and only crystal materials were produced in preliminary experiments. Further work was based on the concept that some chalcogenide glasses represent a system of solid solutions. I t has been mentioned above that As 2 S 3 and As 2 Se 3 are of the chainlaminate structure. Proceeding from one of the conditions for the formation of solid solutions, namely similarity in structure, one had, in order to obtain compound oxychalcogenide glasses, to take an oxide with a structure similar to the one described above. Among the known oxides, antimony trioxide has a laminate structure. Already the first experiments on the synthesis of materials in the system As 2 S 3 -Sb 2 0 3 carried out by the techniques described above have shown that the alloys of these compounds produce typical glasses up to an Sb 2 0 3 -content of 5 0 % . The experiments revealed a fairly large region of glass formation in the system As 2 S 3 -As 2 Se 3 Sb 2 0 3 , as shown in Fig. 24a. At the accepted conditions of preparation two immiscible phases are formed at Sb 2 0 3 -contents above 10%. As is well known, already M E N D E L E E V believed that by some of their properties glasses could be considered as substitutional solid solutions, and that the

Vitreous Semiconductors (II)

729

Fig. 24. Glass-forming regions in alloys of chalcogenides with some oxides

conditions of their formation in glasses are less critical than is the case with crystal materials. This idea initiated an attempt at broadening the investigations by extending it over other oxides with structures differing from the structure of As 2 S 3 and As 2 Se 2 . The results of the work are given in Fig. 24b, c, d, e, f, where the shaded areas of the triangles correspond to the glass-forming regions. Since all compositions were prepared here under identical conditions, the presence of two phases and especially the boundaries of the glass-forming region should be considered as tentative results. The data presented indicate the existence of one more group of vitreous materials whose properties should be thoroughly studied. One may expect in the nearest future the discovery of new types of oxychalcogenide glasses since their study is only beginning. We have carried out preliminary measurements of some parameters of the oxychalcogenide glasses described above. Some of the data obtained are summarized in Table 12. It is seen from the Table that the new type of glasses does not differ much from the chalcogenide glasses. T a b l e 12 Some parameters of oxychalcogenide glasses Item No. 1 2 3 4 5

6 48«

System As2Se 3 -As 2 Se 3 -Sb 2 0 3 AS2S3 -As 2 Se 3 -PbO AS2S3 -As2Se3-HgO GeSe, -As2Se3-HgO Sb2S3 -Sb 2 0 3 -HgO region N1 region N2 AS2S3 -As2Se3-CuO

a ( ß " 1 cm" 1 ) 10" 1 3 10" 1 3 10- 1 3 10- 1 2

to to to to

10" 12 10- 12 10- 10 10- 11

10- 1 3 to 10" 12 10- 1 3 to 10- 12 10- 1 0 to 10" 5

d (g/cm 3 )

Tg (°C) 194 to 194 to 197 to 212 to

215 208 208 260

241 to 255 278 to 318 190 to 238

3.661 3.545 4.392 4.498

to to to to

4.747 3.948 4.605 4.675

4.115 to 4.393 4.237 to 5.090 3.281 to 4.783

AH (kg/mm 2 ) 103 93 93 114

to to to to

145 145 145 189

129 to 189 258 to 306 129 to 189

730

B . T . KOLOMIETS

The discovery of a large group of vitreous materials, that is, substances without a long-range order, possessing clearly pronounced semiconducting properties has led to the development of the theory of amorphous semiconductors. The major work in this direction has been done by G U B A N O V [ 4 2 , 4 3 , 4 5 ] . His considerations supported by a quantum-mechanical approach and calculations may be summarized briefly as follows. The melting of a substance is accompanied by the disappearance of the longrange order whereas the short-range order undergoes only slight distortions. The energy spectrum of such a system consists of bands just, as in the case of crystals, however the disordering causes a certain broadening of the bands which results in a narrowing of the energy gap. This point of view has got a strong confirmation in the course of the study of arsenic selenide in the glassy and crystal state. Measurements of the conductivity, its temperature dependence, and photoconductivity have shown unambiguously that the transition from glass to crystal in such a simple substance is accompanied by a broadening of the energy gap. The changes of the conductivity and of the energy gap are in a good quantitative agreement with the criteria of G U B A N O V . As follows from the above material, it has been established experimentally that atoms of an impurity in the vitreous chalcogenide semiconductors described here do not play such a role in conduction as they do in crystals. A theoretical consideration indicates the following three most probable causes accounting for this fact. 1. Impurity atoms in an amorphous substance occupy other sites than in a crystal. If, for instance, in a crystal an impurity atom is located in a vacancy of the lattice (a substitution impurity), in an amorphous substance it may become an interstitial species and, as such, it will play a completely different role. The probability of an impurity atom becoming an interstitial in an amorphous substance is much greater than that for a crystal because of the relative looseness of the amorphous substance, the absence of a strict order in the atomic arrangement, and the resulting wide interstices. 2. Although the atoms of impurities in an amorphous substance are located at approximately the same sites as in a crystal, they cause such a rearrangement of the surrounding atoms that the donor levels come closer to the filled band, and the acceptor levels — to the conduction band. I t is evident that both donor and acceptor levels will in this case cease to play an appreciable role in conduction. 3. In liquids and amorphous substances (glasses, in our case) there exist great fluctuations in the short-range order capable of producing local energy levels. These "fluctuation" levels can trap electrons or holes thus neutralizing the effect of donors or acceptors and causing the absence of impurity conduction. The concept of the presence of acceptor-type fluctuation levels in amorphous substances begins to receive experimental confirmation. Quite recently, for example, after the publication of G T J B A N O V ' S work on fluctuation levels, in the course of studying the electrical properties of the glass Tl2Se • As2Te3 in the low temperature region, local levels of the acceptor type have been found in the forbidden band of this substance which lie at 0.2 to 0.3 eV. The problem of the role of impurities in amorphous substances was investigated also by F I S H E B [ 4 7 ] . Besides a purely scientific interest, the new vitreous materials described here begin to find practical applications.

Vitreous Semiconductors (II)

731

The properties of chalcogenide materials may be used in the following practical fields. A broad transmission spectrum is advantageous for optical technology, a high photosensitivity may be used in designing vidicons, the low softening temperature — to make vacuum-tight semiconductor devices (silicon and germanium diodes and triodes), and so on. These items do not by far cover all the possible fields of applications, they rather reflect the extent of scientific research carried out during a comparatively short period of time. As the investigations become broader and more comprehensive, new properties of practical value will be discovered. One may briefly summarize the results obtained in the course of the investigation of new groups of chalcogenide and, in part, of oxychalcogenide glasses in the following way: 1. Chalcogenide glasses represent an extensive group of materials whose optical, electrical, and other properties can vary within a fairly wide range with composition. A large group of these glasses represents typical semiconductors whose distinctive features are the absence of the long-range order, homogeneity (the absence of the crystal-to-crystal contact), the independence of small amounts of impurities, a small mobility of current carriers, etc. 2. The complex investigation of the relationship between the properties of chalcogenide glasses and their compositions permits to draw the conclusion that glasses may be systems of solid solutions of substitution, and that the laws found for crystal substances may apparently be extended to cover vitreous substances. 3. The presence of two and three immiscible phases indicates the existence of different structures in chalcogenide glasses. 4. There are some indications that the short-range order does not undergo considerable changes during the transition from the vitreous into the crystal state. I t may be noted t h a t the material presented in this article covers only general information on the properties of amorphous substances which have become recently an object of intense study for a large number of both theorists and experimenters. A broadening of research will undoubtedly be advantageous for the theory of solid state as well for future practical applications. As for the future, it is necessary to continue the investigation of the electrical properties of new glasses both in the solid and liquid, melted, state; to establish the boundaries of the glass-forming region in chalcogenide glasses of more complex compositions; to investigate the principal physicochemical properties; to broaden research on the discovery and study of the nature of local levels in the forbidden band of chalcogenide semiconductors and on the study of the behaviour of current carriers in amorphous substances. Due to their high conductivity and crystallizability, the vitreous chalcogenide semiconductors represent interesting objects for the study of the mechanism and kinetics of crystallization. References See part I, pages 371/372 . (Received

July 23,

1964)

Original Papers phys. stat. sol. 7, 733 (1964) Institut für Allgemeine Metallkunde und Metallphysik, Technische Hochschule Aachen (a) und Max-Planck-Institut für Eisenforschung, Düsseldorf (b)

Elektronenmikroskopische Bestimmung der Orientierungsverteilung der Kristallite in gewalztem Kupfer Von K . L Ü C K E ( a ) , H . P E R L W I T Z ( a ) u n d W . PITSCH ( b )

Es wird ein Meßverfahren beschrieben, nach dem durch elektronenmikroskopische Peinbereichsbeugung die Orientierungsverteilung der Kristallite in verformten Metallblechen quantitativ bestimmt werden kann. Dieses Verfahren wird auf bei Raumtemperatur gewalztes Kupfer angewendet. Die dabei erhaltenen Ergebnisse stimmen im wesentlichen mit entsprechenden röntgenographischen Texturbestimmungen überein. Darüberhinaus zeigte sich, daß die untersuchte Kupferwalztextur keine ausgeprägten Maxima in der Orientierungsverteilung besitzt. Statt dessen wurde gefunden, daß der Hauptteil dieser Textur relativ gleichmäßig verteilt ist über einen Orientierungsbereich, der durch die Lagen (011) [211] und (112) [111] begrenzt wird. A method is described for measuring the distribution of orientations of crystals in deformed metals by means of selected area diffraction with the electron microscope. The method is used to investigate quantitatively the texture of copper rolled at room temperature. The results obtained agree essentially with those of classical X-ray measurements. However, in detail it was found, that there is no pronounced maximum in the distribution of orientations. The main part of the rolling texture of Cu consists of a rather homogeneous distribution of orientations over a range, which is bounded by (Oil) [211] and(112) [111]. 1. Einleitung Bei vielkristallinen Metallkörpern ist die Orientierungsverteilung der Kristallite, die sogenannte Textur, von wissenschaftlichem und auch von technischem Interesse. Zur Angabe dieser Texturen wird gewöhnlich die Häufigkeitsverteilung einer bestimmten kristallographischen Richtung {h kl} über alle räumlichen Lagen röntgenographisch gemessen und in einer Polfigur dargestellt [1]. Da jedoch die Messung einer einzelnen Kristallrichtung nur zwei Koordinaten enthält, gibt die genannte Methode grundsätzlich keine vollständige Auskunft über die Orientierungen der Kristallgitter, die erst durch drei Koordinaten bestimmt sind. Die dritte Koordinate ist beispielsweise eine Drehung um die festgehaltene Kristallrichtung {h kl}. U m trotz dieser Begrenzung in der Methode über die Orientierungsverteilung der Kristallite eine Aussage zu erhalten, wird meistens versucht, aus den Schwerpunkten der röntgenographisch gemessenen Polfiguren die Orientierungsverteilung der Kristallite zu erraten. Während dieses Vorgehen bei Orientierungsverteilungen, die nur wenige und scharf ausgeprägte Vorzugslagen enthalten, häufig zum Erfolg führt [1], muß es bei komplizierteren und insbesondere bei verschmierten Verteilungen grundsätzlich versagen.

734

K . LÜCKE, H . PERLWITZ u n d W . PITSCH

Deshalb wurde wiederholt versucht, die Kristallorientierungen direkt an einzelnen Kristallen zu messen. Dies ließ sich bisher bei großen Kristalliten, z. B . bei solchen in grobkörnig rekristallisiertem Material mittels röntgenographischer [2] oder lichtoptischer [3] Verfahren durchführen. In sehr feinkörnig rekristallisiertem und insbesondere in verformtem Material sind jedoch die gleichorientierten Kristallbereiche für dieses Verfahren, selbst bei Anwendung von Feinfokusröhren zu klein. E s lassen sich aber in einem Elektronenmikroskop Kristallbereiche, die nur etwa 1 /um groß sind, ausblenden und ihre Orientierung durch Elektronenbeugung bestimmen. Deshalb erschien es möglich, die Orientierungsverteilung von feinkörnigen oder verformten Metallblechen elektronenmikroskopisch direkt zu messen. In einer ersten Notiz wurde die Durchführbarkeit solcher Messungen am Beispiel der Textur eines rekristallisierten Kupferbleches gezeigt [4]. In der vorliegenden Arbeit soll über die Durchführung solcher Untersuchungen an stark verformten Proben berichtet werden. Dabei wird das elektronenmikroskopische Meßverfahren kritisch beschrieben, und es werden die an gewalzten Kupferblechen erhaltenen Ergebnisse dargestellt und mit den entsprechenden röntgenographischen Texturbestimmungen verglichen. E s soll darauf hingewiesen werden, daß ähnliche Untersuchungen gegenwärtig ebenfalls von F . H A K S S N E R und M. W I L KEN s [5] durchgeführt werden. Die oben erwähnten Unzulänglichkeiten der Polfigurenmethode finden am Beispiel der Kupfer-Walztextur ihren Ausdruck darin, daß für die Polfiguren dieser Textur, obgleich sie relativ einfach sind, in der Literatur mehrere verschiedene Interpretationen vorgeschlagen wurden [6]. So wurden beispielsweise frühzeitig die Lagen (135) [ 2 l l ] und die Doppellage (011) [2lT] - f (112) [111], später an Hand quantitativer Polfiguren die Lage (5, 8, 14) [11, 5, 7] + (2, 9, 11) [9, 4, 5] angegeben [7]. Von den anderen Indizierungen sei nur noch die als Nebenkomponente aufgeführte Würfellage (001) [100] und die 2 = £k, 2 {K = q — q') orthogonal to the plane of the vectors q and q'. With reference to Fig. 1, we have the following relations: = « K , l COS«f — EK, 3 s i n

£q,2

=

(7a)

£K,2,

3 = «K, 1 sin