CREATION OF AsGa DEFECTS BY PLASTIC DEFORMATION OF GaAs CRYSTALS

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CREATION OF AsGa DEFECTS BY PLASTIC DEFORMATION OF GaAs CRYSTALS

T. Figielski, T. Wosi_ski, A. Morawski

To cite this version:

T. Figielski, T. Wosi_ski, A. Morawski. CREATION OF AsGa DEFECTS BY PLASTIC DEFOR- MATION OF GaAs CRYSTALS. Journal de Physique Colloques, 1983, 44 (C4), pp.C4-353-C4-357.

�10.1051/jphyscol:1983442�. �jpa-00223061�

JOURNAL DE PHYSIQUE

Colloque C4, suppl6ment au n09, Tome 44, septembre 1983 page C4-353

CREATION OF AsGa DEFECTS BY P L A S T I C DEFORMATION OF GaAs CRYSTALS

T. F i g i e l s k i , T . Wosiriski and A . Morawski

I n s t i t u t e of Physics, Polish Academy o f Sciences, AZ.Lotnikdw 32, 02-668 Warsaw, Poland

~ G s u m ; . Les differents r&ultats concernant l a c r e a t i o n e'c l e s p r o p r i & t & s des d e f a u t s " a d t i s i t e n a r s e n i c dans l e s c r i s t a u x GaAs plastiquement d6form6s s o n t pr4sent6s. Les d g f a u t s A s G a s o n t i d e n t i f i 6 s comme l e s p i 6 g e s e l e c t r o n s dominants EL^).

Deux m6canismes diffErents de l e u r f o r m a t i o n pendant l e mouve- ment d e s d i s l o c a t i o n s sons d i s c u t & s . On mentionne l e r 8 l e pos-

s i b l e d e s d 6 f a u t s A%, dans l e fonctionnement d e s 616ments op- t o 6 1 e c t r o n i q u e s .

Abstract. - Various r e s u l t s concerning t h e c r e a t i o n and proper- t i e s of a r s e n i c a n t i s i t e d e f e c t s i n p l a s t i c a l l y deformed GaAs c r y s t a l s a r e compiled. The A s G a d e f e c t s a r e i d e n t i f i e d a s t h e dominant e l e c t r o n t r a p s EL^) . Two d i f f e r e n t mechanisms of their c r e a t i o n d u r i n g t h e d i s l o c a t i o n motion a r e discusaed.

possible r o l e of A s G a d e f e c t s i n o p t o e l e c t r o n i c d e v i c e o p e r a t i o n i s men- tioned.

The EPR and DLTS t e c h n i q u e s have been employed f o r t h e i n v e s t i g a - t i o n of t h e d i s l o c a t i o n - r e l a t e d e l e c t r o n s t a t e s i n GaAs c r y s t a l s s u b j e c t e d t o a p l a s t i c deformation.

The c r y s t a l s i n v e s t i g a t e d were LEC-grown with i n i t i a l e t c h p i t

4 2

d e n s i t y of about 10 cm- . The Cr-doped, s e m i - i n s u l a t i n g GaAs c r y s - t a l s were used f o r t h e EPR measurements, and n-type c r y s t a l s with t h e e l e c t r o n c o n c e n t r a t i o n 1.5 x

I 6 cme3 were used f o r t h e DLTS s t u d y . The samples were p l a s t i c a l l y deformed by u n i a x i a l compression p a r a l l e l t o t h e 12131 d i r e c t i o n , a t t h e temperature of 4 0 0 ' ~ i n t h e atmosphere of 92% N2 and

H2 [ I ] .

1.

ZPR r e s u l t s . - New i s o t r o p i c l i n e s have been found bg Wosinski [1,2] t o a p p e a r i n t h e EPR spectrum of t h e c r y s t a l s a f t e r t h e i r de- f o r n a t i o n . These l i n e s have been recognized by Weber e t a l . [31 t o b e l o n g t o t h e q u a r t e t of h y p e r f i n e s t r u c t u r e o r i g i n a t i n g from t h e i s o l a t e d As;: a n t i s i t e d e f e c t [ 4 , 5 ] . These l i n e s c o u l d be observed

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983442

C4-354 JOURNAL DE PHYSIQUE

a l s o i n undeformed samples but t h e i r i n t e n s i t i e s were c l o s e t o t h e d e t e c t i o n l i m i t . The EPR s i g n a l might be quenched by i r r a d i a t i o n of t h e c r y s t a l with l i g h t of hv exceeding two t r e s h o l d v a l u e s : 0.75 eV and 1.05 eV a t which a n e l e c t r o n from a s i n g l y occupied s t a t e of t h e c e n t e r i s removed t o t h e r- o r L-minimum i n t h e conduction band, r e - s p e c t i v e l y [6].

2. DLTS r e s u l t s . - Contrary t o t h e deformed s i l i c o n i n which a new, r i c h s t r u c t u r e a p p e a r s i n DLTS spectrum [ 7 ] , t h e Gahs c r y s t a l s show o n l y moderate changes a f t e r t h e i r deformation 181. These changes con- s i s t of two folowing e f f e c t s (Pig. I ).

7 -

n - O a A s

UNDEFORMED

Fig.1. DLTS s p e c t r a of undefor- med ( u p p e r c u r v e ) and t h e defor-

1 med t o t h e s t r a i n of 5.5% sam- p l e s ( l o w e r c u r v e ) , o b t a i n e d a t

E = 5 . 5 %

a window r a t e of

s-'. Acti-

v a t i o n e n e r g i e s of s e p a r a t e t r a p s i n eV a r e shown below t h e c u r v e s . Note t h e s c a l e s of AC/C

I I I

* , & ? ,

f o r b o t h c u r v e s d i f f e r by a fa@-

Y X ) ( ~ O ~ M ) ~3~~O) 3 ~ )

tor 2 .

T(K)

-

E l e c t r o n t r a p s of a new type appear a f t e r t h e deformation, charac- t e r i z e d by t h e a c t i v a t i o n energy of 0.37 eV and t h e c r o s s - s e c t i o n f o r e l e c t r o n c a p t u r e of 4

cm2 ( t h e peak l a b e l l e d D i n Fig. I ) . The c o n c e n t r a t i o n of t h e s e t r a p s i s 5 x

cm-3 i n t h e sample de- formed t o t h e s t r a i n of 5.5%. A s f o l l o w s from t h e voltage-dependence o f t h e DLTS s i g n a l , t h e s e t r a p s a r e perhaps not uniformly d i s t r i b u - t e d i n t h e d e p t h of t h e sample. T e n t a t i v e l y , t h e s e t r a p s might be a t t r i b u t e d t o d i s l o c a t i o n - i n d u c e d e l e c t r o n s t a t e s .

The second i m p o r t a n t e f f e c t of t h e deformation i s a d i s t i n c t i n c -

r e a s e i n t h e c o n c e n t r a t i o n of t h e dominant e l e c t r o n t r a p s , commonly termed gL2. The a c t i v a t i o n energy of t h i s t r a p i s 0.82 0.02 eV and i t s c r o s s - s e c t i o n f o r e l e c t r o n c a p t u r e i s -1 x 1 0 " ~ cm2. These t r a p s a r e h a r d l y s a t u r a b l e , i . e . when i n c r e a s i n g t h e f i l l i n g p u l s e d u r a t i o n time ( t ) i n t h e DLTS experiment, t h e s i g n a l amplitude r i s e s only s l i g h t l y a s l n t P Such f e a t u r e i s p r e d i c t e d f o r l i n e a r a g g r e g a t i o n s o f c e n t e r s , when t h e charge of e l e c t r o n s t r a p p e d P- a t t h e c e n t e r s gives r i s e t o a r e p u l s i n g e l e c t r o s t a t i c p o t e n t i a l l i n e a r l y dependent on t h i s charge d e n s i t y [a].

3. I d e n t i f i c a t i o n of 2L2 t r a p s a s A s G d e f e c t s . - I n t h e t a b l e s b e a

low t h e c o n c e n t r a t i o n s o f BL2 t r a p s and

paramagnetic c e n t e r s i n t h e sarnples s u b j e c t e d t o v a r i o u s s t r a i n s a r e l i s t e d .

correspondence

Table 1 Table 2

C o n c e n t r a t i o n of EL2 t r a p s C o n c e n t r a t i o n

I ^{s m p l e N} ( ~ m - ~ ) sample-

as-grown a s-gro wn

2% s t r a i n 1.6% s t r a i n

5.5% s t r a i n 3.4 x 10 5.6% s t r a i n

of

c e n t e r s N ( ~ m ' ~ ) I

between t h e r e s p e c t i v e v a l u e s quoted i n t h e two t a b l e s i s s t r i k i n g . It s t r o n g l y s u g g e s t s t h a t t h e p a r a a a g n e t i c c e n t e r , observed i n t h e

spectrum and a t t r i b u t e d t o

, a s w e l l a s t h e EL2 e l e c t r o n

t r a p observed i n t h e DLTS spectrum, a r e due t o t h e same d e f e c t . So, t h e dominant, e l e c t r i c a l l y a c t i v e d e f e c t s i n GaAs a r e a o s t probably t h e a r s e n i c a n t i s i t c s . Noreover, t h e s e d e f e c t s a r e produced i n a con- s i d e r a b l e amount d u r i n g t h e p l a s t i c deformation of t h e c r y s t a l . T h e s e c o n c l u s i o n s a r e of g r e a t importance f o r technology of GaAs d e v i c e s .

4. Climb-related mechanism of AsG-, formation. - The s i m p l e s t con- c e p t t o understand t h e mechanism of c r e a t i o n of t h e d e f e c t s d u r i n g t h e c r y s t a l defamation i s t h a t t h e y are formed by a d i r e c t r e a c t i o n between g a l l i u m vacancy and i n t e r s t i % i a l a r s e n i c : VG, + A s i - ^{A s Ga'}

A s i t h a s been claimed by deber e t a l . [ 3 ] , t h e VGa needed f o r t h e

r e a c t i o n can be c r e a t e d f r o a s u p e r s a t u r a t i o n of i n t e r s t i t i a l A s a t o m

i n t h e p r o c e s s of d i s l o c a t i o n climb a c c o r d i n g t o t h e r e a c t i o n

d c ---VGa, where dc d e n o t e s t h e ( c o n p l e t e ) c l i m b s t e p . Tbe d r i v i n g

f o r c e f o r t h i s r e a c t i o n may b e , f o r i n s t a n c e , t h e s m a l l e r c h e n i c a l

p o t e n t i a l of VGa compared with Asi. It seems, however, t h a t a t t h e

temperature a s low a s 4 0 0 ' ~ t h e climb i s a minor e f f e c t i n t h e d i s -

l o c a t i o n motion, and t h e r e f o r e we l o o k r a t h e r f o r t h e g l i d e - r e l a t e d

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JOURNAL DE PHYSIQUE

mechanism of a n t i s i t e f o r m a t i o n .

5. G l i d e - r e l a t e d mechanism of A s G a f o r m a t i o n . - It h a s been shown by P i g i e l s k i [ 9 ] t h a t A s G a d e f e c t s may, be c r e a t e d from i n t e r s t i t i a l a r s e n i c atozos i n t h e p r o c e s s of t h e i r i n t e r a c t i o n w i t h g l i d i n g 60°

d i s l o c a t i o n s ( P i g . 2 ) . L e t u s t a k e i n t o c o n s i d e r a t i o n a d i s s o c i a t e d g l i d e - s e t 60' d i s l o c a t i o n o f t h e As-type which i n i t s g l i d e motion

P i g . 2. ( a ) tom a r r a n g e m e n t i n t h e c o r e o f u n d i s s o c i a t e d g l i d e - s e t 60' d i s l o c a t i o n . ( b ) Suc- c e s s i v e s t a g e s o f a n t i s i t e de- f e c t f o r m a t i o n .

a p p r o a c h e s t h e A s atom p l a c e d i n a n i n t e r s t i t i a l p o s i t i o n . Due t o tb i n t e r a c t i o n between tbis atom a n d t h e d i s l o c a t i o n t h e l a t t e r becomes l o c a l l y c o n s t r i c t e d ( s t a g e 1 i n P i g . 2 b ) . The A s atoin i s t h e n absorbed i n t h e d i s l o c a t i o n c o r e , s o it d i s s a p e a r s as a n i n t e r s t i t i a l d e f e c t b u t g i v e s r i s e t o t h e f o r m a t i o n o f a d o u b l e j o g o f one atom h e i g h t o n t h e d i s l o c a t i o n l i n e . Such i n c o m p l e t e j o g l e a d s t h e d i s l o c a t i o n l i n e o u t f r o n a p l a n e of t h e g l i d e s e t t o t h e a d j a c e n t p l a n e of t h e s h u f f l e s e t . The d i s l o c a t i o n moves f u r t h e r t o g e t h e r w i t h i t s d o u b l e j o g and l e a v e s a n u n d i s t u r b e d c r y s t a l l a t t i c e behind. The hs atom, which b e f o r e a b s o r p t i o n was i n t h e i n t e r e s t i t i a l p o s i t i o n , bacoaes now b u i l t i n t o bhe l a t t i c e a n t i s i t e p o s i t i o n ( s t a g e 2 i n ~ i g , 2 b ) . T h e

jogged d i s l o c a t i o n d i s s o c i a t e s i n i t s f u r t h e r n o t i o n i n t o unjogged l i n e a n d i n t e r s t i t i a l G a ( s t a g e 3 i n Pig.2b). The p r o c e s s i s e q u i v a - l e n t t o t h e r e a c t i o n

+ GaGa- A s G a + Gai.

6. K i l l e r s o f luminescence: d i s l o c a t i o n s o r haGa? - ^A p r e c i z e 1:1

c o r r e s p o n d e n c e between d a r k s p o t s a n d d i s l o c a t i o n e t c h p i t s h a s of-

t e n been o b s e r v e d ~ i t h electron-beam-induced l u n i n e s c e n c e i n GaAs

a n d o t h e r 111-V aemiconduc t o r s [

. Commonly, d i s l o c a t i o n s have

been c o n s i d e r e d a s t h e s i n k s f o r c h a r g e c a r r i e r s , r e s p o n s i b l e f o r tk

d r a s t i c r e d u c t i o n of luminescence. An a l t e r n a t i v e e x p l a n a t i o n o f

t h e s e o b s e r v a t i o n s may be t h a t t h e c l o u d s o f a r s e n i c a n t i s i t e d e f e c t s

s u r r o u n d i n g t h e d i s l o c a t i o n s i n G a i ~ s a r e t h e main c e n t e r s of nonra- d i a t i v e r e c o m b i n a t i o n a n d t h e y l e a d t o t h e d a r k s p o t a p p e a r i n g . Con- s e q u e n t l y , one may a s k whether t h e d i s l o c a t i o n s t h e m s e l v e s o r d i s - l o c a t i o n - c r e a t e d a n t i s i t e d e f e c t s a r e r e s p o n s i b l e f o r a d r o p i n ra- d i a t i v e e f f i c i e n c y a n d n e x t f o r t h e f a i l u r e o f o p t o e l e c t r o n i c d e v i - c e s i n which d u r i n g t h e i r o p e r a t i o n a d i s l o c a t i o n - r e l a t e d mechanism o f d e g r a d a t i o n dominates. E x p e r i m e n t a l a e t h o d vihich c a n h e l p t o a n s - vier t h i s q u e s t i o n may be t h e s c a n n i n g DLTS (sDLTS). P r e l i n i n a r y i n - v e s t i g a t i o n s o f p l a s t i c a l l y d e f o r a e d Gaks have been done w i t h t h i s method i n t h e I n s t i t u t f d r F e s t k B r p e r p h y s i k und i3lektronenmikroskopie

i n H a l l e [ I I] . C h a r a c t e r i s t i c l*mountains a n d v a l l e y s n s t r u c t u r e i s d i s p l a y e d on t h e pseudo t h r e e - d i m e n s i o n a l SDLTS topogram ( ~ i g . 3 1 , which seems t o j u s t i f y a r o d - l i k e d i s t r i b u t i o n o f EL2 t r a p s . The l a t - t e r i s c o n s i s t e n t w i t h t h e c o n c e p t s p r e s e n t e d i n t h i s l e t t e r .

F i g . 3. XL2 t r a p d i s t r i b u t i o n rneasu- r e d w i t h t h e SDLTS a t a t e m p e r a t u r e o f 9 3 O ~ , window r a t e o f 33 s-' a n d e l e c t r o n beam v o l t a g e o f

kV.

a (

a ) q u a s i t h r e e - d i m e n s i o n a l p i c t u r e ,

s i n g l e s c a n t a k e n from t h e

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w 0 r i a t i o n i n t r a p c o n c e n t r a t i o n . R e f e r e n c e s

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1

I .BRdITENST&IN, 0 , , dOSINSK1, T.,

s t a t . s o 1 . ( a ) , t o

p u b l o