X-RAY AND SCANNING CATHODOLUMINESCENCE IMAGING OF SMALL-ANGLE GRAIN BOUNDARIES AND DISLOCATIONS IN CdTe CRYSTALS

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X-RAY AND SCANNING

CATHODOLUMINESCENCE IMAGING OF SMALL-ANGLE GRAIN BOUNDARIES AND

DISLOCATIONS IN CdTe CRYSTALS

M. Klimkiewicz, J. Auleytner

To cite this version:

M. Klimkiewicz, J. Auleytner. X-RAY AND SCANNING CATHODOLUMINESCENCE IMAGING OF SMALL-ANGLE GRAIN BOUNDARIES AND DISLOCATIONS IN CdTe CRYSTALS. Journal de Physique Colloques, 1983, 44 (C4), pp.C4-313-C4-316. �10.1051/jphyscol:1983437�. �jpa-00223056�

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Colloque C4, supplément au n°9, Tome 44, septembre 1983 page C4-313

X - R A Y A N D SCANNING C A T H O D O L U M I N E S C E N C E IMAGING OF S M A L L - A N G L E GRAIN B O U N D A R I E S A N D D I S L O C A T I O N S IN C d T e C R Y S T A L S

M. Klimkiewicz and J. Auleytner

Institute of Physios, Polish Academy of Sciences, Warszawa, Poland

Résumé - En utilisant d'une part la topographie de rayons X (RXT), et d'autre part la microscopie électronique à balayage en mode cathodoluminescence (CL-IR), nous sommes en mesure de visualiser les défauts du réseau dans les monocristaux de CdTe. La possibilité d'identification du défaut est un avantage de la technique RXT.

De plus, la surface examinée peut être imagée. La cathodoluminescence garantit cependant une meilleure résolution. Les défauts observés en cathodoluminescence dans des cristaux de CdTe ont été identifiés comme des sous-joints et des dislocations à vis.

Abstract - By employing the Reflection X-ray Topography (RXT), on one hand, and the cathodoluminescence (CL-IR) mode of operation of the Scanning Electron Microscope, on the other hand, we are able to visualize the lattice defects in CdTe single crystals. The possibility of defect identification is the advantage of the RXT technique. Moreover, the examined surface can be imaged as a whole.

Cathodoluminescence however, guarantees higher resolution. The defects in CdTe crystals, observed in cathodoluminescence images, have been identified as small-angle boundaries and screw dislocations.

1 - INTRODUCTION

Complementary employment of Reflection X-ray Topography (RXT) and Scanning Ga,thodoluminescepce (SCL) can successfully serve for. ident.ification of imaged defects, which is shown clearly in the present paper. At it has already been reported (KLIMKIEWICZ, AULEYTNER, WARMINSKI, 1981), a correlation can be found between the images of defects, obtained by using the above-mentioned techniques, provided the required experimental conditions are preserved.

The acknowledged advantage of the RXT technique consists in the fact that the image of the sample surface, as a whole, is obtained with distinguishable structural defects. However, the resolution of electron microscopic images is considerably higher although they offer an insight into a small section of the tested sample only.

1. Sample characterization.

The paper presents the results of investigations of CdTe crystals prepared by Bridgman method from solution with excess of tellurium. The sample to be examined had a form of a slice cut along the({110} plane. It was subjected to to mechanical polishing with a diamond paste, washed in alcohol in an ultra- sonic desintegrator, and finally chemically polished in 2% bromine solution in methanol. The investigations were performed on the samples not thicker than 200 ytn • The sample shapes were, in consequence, reasonably irregular but X-ray topographs could satisfactorily be obtained.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983437

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2. Experimental arranqements.

Reflection X-ray t o p o g r a ~ h s (RXT) were obtained i n an o s c i l l a t i n g s l i t camera (AULEYTNER, 1971) by using an X-ray tube with i r o n t a r g e t . FeKB r a d i a t i o n has been used f o r imaging c r y s t a l s u r f a c e s t r u c t u r e . Which r e f e r s t o t h e transmis- sion X-ray Topographs (TXT) they were p o s s i b l e with t h e Lana method employing Ka Cu r a d i a t i o n . Microscopic observations were c a r r i e d o u t using t h e SCL operation mode of EPMA JXA - 50A. The remaininp modes, includinp SEI and BEI, served f o r s u r f a c e control only.

3 . Results and discussion.

Upon inspection o f transmission X-ray tooographs numerous d e f e c t s have been recognized i n t h e c r y s t a l s t e s t e d , some of them beina t h e small-angle boundaries and t h e o t h e r a c t i n g a s s i n g l e d i s l o c a t i o n s . A number of d e f e c t s could hardly be i d e n t i f i e d owing t o t h e i r high d e n s i t y . SCL p i c t u r e e x h i b i t e d a d i s t i n c t c o n t r a s t i n a form of a d i s o r d e r of dark s p o t s t o g e t h e r with dark l i n e s arranged i n networks. Under higher magnifications t h e l a t t e r can be recoanized a s rows of more o r l e s s denesely d i s t r i b u t e d s o o t s ( F i g . 1 and 2 ) . When c o r r e l a t i n g t h e SLC images with RXT topographs obtained i t can be s t a t e d , beyond any doubts, t h a t t h e l i n e s observed i n cathodoluminescence p i c t u r e s e x a c t l y correspond t o those i n X-ray images ( F i g . 1 , 2 , 3 ) . The network of white and dark 1 i n e s , appearing i n X-ray topographs, r e p r e s e n t s t h e system of small-angle boundaries. When t h e RXT geometry, beam width, m a a n i f i c a t i o n , and c r y s t a l - f i l m d i s t a n c e a r e known, t h e m i s o r i e n t a t i o n angle between t h e a d j a c e n t regions of t h e c r y s t a l s , demarkated by t h e given small-angle boundary, can be evaluated. The l i n e a r d e n s i t y of d i s l o c a t i o n s a t t h e boundary can thus be determined (AULEYTNER, 1967). I t ought t o be n o t i c e d , however t h a t t h e space e l e c t r o n i c charge a t t h e d i s l o c a t i o n implies t h e CL-IR image of i t s c r o s s - s e c t i o n t o be a s p o t of diameter a t l e a s t 1 um. On t h e o t h e r hand, i t has been found from p r a c t i c a l X-ray topography t h a t a m i s o r i e n t a t i o n of a t l e a s t 15" i s required t o v i s u a l i z e t h e c o n t r a s t of a boundary p r e s e n t experimental c o n d i t i o n s . Let us exemplify i t considerin9 t h e arrow-marked boundary i n t h e cathodol u m i nescence p i c t u r e : t h e determinable spacing between t h e s p o t s equals 5.2 pm/ t h e m i s o r i e n t a t i o n angle of t h e regions equals 18"/. The above c o n s i d e r a t i o n s make c l e a r t h a t t h i s p a r t i c u l a r s e c t o r of t h e boundary gives a weak c o n t r i b u t i o n t o t h e RXT image, and only t h e o t h e r p a r t s g e t c l e a r l y v i s i b l e . Which r e f e r s t o t h e region with higher d i s l o c a t i o n d e n s i t y contained within he boundaries, a random d i s t r i b u t i o n of d i s l o c a t i o n s

k ^-2

i s observed of d e n s i t y 10 cm .

Concluding, t h e d e f e c t s imaged i n t h e cathodoluminescence p i c t u r e s a r e undoubtedly recognized a s t h e small-angle boundaries of t h e t i l t - t w i s t type and t h e d i s l o c a t i o n s nearly normal t o t h e c r y s t a l s u r f a c e . I t becomes thus evident t h a t t h e RXT and SCL techniques a r e complementary ones and, when employed i n t h e examination of t h e same o b j e c t , they can provide a univocal i n t e r p r e t a t i o n of imaged d e f e c t s i f only t h e required experimental c o n d i t i o n s a r e preserved.

References.

AULEYTNER, J.,X-ray methods i n t h e study of d e f e c t s i n s i n o l e c r y s t a l s , Pergamon P r e s s , 1967.

AULEYTENER, J . , Acta Phys.Po1.

z,

KLIMKIEWICZ M. ,AULEYTNER J ., WARMINSKI T . , Crystal Research and Techno1 ogy, 16.2, 175-181, 1981.

F i g . 1 Scanning cathodoluminescence /C1-IR/ and X-ray topographic /RXT/ images o f g r a i n boundaries and d i s l o c a t i o n s i n a t b i n CdTe sample. The arrows i n d i c a t e t h e same v e c t o r o f a boundary.

Fig.3 Low angle g r a i n boundary w i t h i n d i v i d u a l d i s l o c a t i o n s v i s i b l e as dark spots ; C1-IR image. The arrow i n here and those shown i n Fig.1 are p o i n t i n g o u t t h e same s e c t o r o f t h e boundary.

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