EPR OF DISLOCATIONS IN SILICON

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EPR OF DISLOCATIONS IN SILICON

E. Weber, H. Alexander

To cite this version:

E. Weber, H. Alexander. EPR OF DISLOCATIONS IN SILICON. Journal de Physique Colloques,

1979, 40 (C6), pp.C6-101-C6-106. �10.1051/jphyscol:1979621�. �jpa-00219037�

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JOURNAL DE PHYSIQUE CoZloque C6, s u p p l h e n t au $6, tune 40, j u i n 1979, page C6-I01

EPR OF D I S L O C A T I O N S I N S I L I C O N E. Weber and H. Alexander

Abteilung fiir MetaZZpkysik i r n I I . Physikaliscken I n s t i t u t , U n i v e r s i t a t zu KoZn, D 5000 Ktiln, F.R.C.

Resume.- Une revue des mesures par RPE des spectres associes aux d i s l o c a t i o n s e s t donnee, en i n s i s t a n t p a r t i c u l i e r e m e n t sur l e s modeles atomiques envisageables pour ces centres. On oeut deduire des r i c e n t e s mesures des l i g n e s hyperfines c a r a c t e r i s t i q u e s du c e n t r e Si-K1 de nouveaux renseignements sur l ' a r r a n - gement atomique au voisinage de ce centre. On peut c o n c l u r e de ces r e s u l t a t s que l e s centres associes aux d i s l o c a t i o n s sont t r e s probablement l o c a l i s e s s u r l e s d i s l o c a t i o n s ~ a r t i e l l e s des v i s dissociees.

De p l u s , l ' i n f l u e n c e d ' u n e c l a i r e m e n t a e t e etudiee : il a p o a r a i t que l e nombre de c e n t r e a s p i n s apparies c r o i t t a n d i s que l e spectre du c e n t r e Si-K1 d e c r o i t sous i r r a d i a t i o n oar une lumiere d ' e n e r g i e s o i t egale

a

l a l a r g e u r de bande i n t e r d i t e s o i t egale

a

0,68 eV.

Abstract.- Our EPR measurements o f d i s l o c a t i o n soectra i n s i l i c o n a r e reviewed w i t h s p e c i a l emohasize on t h e p o s s i b l e atomic models o f these centres. New i n f o r m a t i o n uoon t h e atomic arranqexient around t h e s i n g l e e l e c t r o n c e n t r e Si-K1 can be deduced from r e c e n t measurements o f h y o e r f i n e l i n e s belonging t o t h i s centre. From these r e s u l t s i s concluded t h a t t h e o a r t i a l d i s l o c a t i o n s o f s p l i t screw d i s l o c a - t i o n s are the most probable l o c a t i o n o f the d i s l o c a t i o n centres. I n a d d i t i o n the e f f e c t o f i l l u m i n a - t i o n on these centres i s discussed : band gap l i g h t as w e l l as l i g h t w i t h 0.63 eV ohoton energy en- hances t h e number o f coupled s p i n centres and decreases t h e Si-K1 spectrum.

1. I n t r o d u c t i o n . - I n t h e l a s t f i f t e e n years e l e c t r o n paramagnetic resonance (EPR) has proved t o be a very powerful t o o l f o r the i n v e s t i g a t i o n o f d e f e c t s i n s i l i c o n , because i t i s a b l e t o y i e l d i n f o r m a t i o n about t h e atomic arrangement around t h e oaramagnetic centres. So f o r a l o t o f r a d i a t i o n induced d e f e c t s d e t a i l e d models i n c l u d i n g even Jahn

-

T e l l e r d i s t o r - t i o n s c o u l d be developed based mainly on the work of G.D. Watkins and J.W. C o r b e t t i n the 6 0 t h (see e.g.

/ I / ) . Also p l a s t i c a l l y deformed s i l i c o n contains broken bonds which g i v e r i s e t o an EPR s i g n a l f i r s t l y found by Alexander e t a l . 1965 /2/ and l a t e r on exa- mined i n v a r i o u s papers/3-lo/.

The number o f paramagnetic e l e c t r o n s present i n a deformed sample turned o u t t o be n o t more than p a r t o f a percent o f the t o p o l o g i c a l l y p o s s i b l e num- b e r o f d a n g l i n g bonds i n t h e produced d i s l o c a t i o n s . Therefore these paramagnetic centres must be l o c a t e d

i n very s p e c i a l d i s l o c a t i o n segments. Ue want t o deduce here m a i n l y from t h e EPR r e s u l t s obtained up t o now what k i n d o f d i s l o c a t i o n s produce t h e EPR spectra and what can be learned from these spectra concerning p o s s i b l e atomic models o f t h e d i s l o c a t i o n core i n s i l i c o n .

2. Central l i n e s : Si-K1 centre.- A f t e r deformation a t a temperature of 650' C t h e EPR spectrum can be devided i n t o a c e n t r a l p a r t and p e r i p h e r a l l i n e s on b o t h s i d e s o f these c e n t r a l l i n e s /6-7/. The c e n t r a l l i n e s c o n s i s t o f v a r i o u s spectra a t d i f f e r e n t temoe- r a t u r e s of measurement (see Fig. 1). Measuring i n

a b s o r o t i o n one centre, c a l l e d by us Si-K1 can o n l y be recorded a t low temperatures uo t o about 60 K whereas a t h i g h e r temperatures new l i n e s emerge which belong t o a t l e a s t t h r e e f u r t h e r c e n t r e s (Si-K3 t o Si-K5) and a l s o form t h e room temoerature spectrum. Compa- r i n g t h e spectra o f c r y s t a l s deformed w i t h an <213>

- a x i s ( f a v o u r a b l e f o r s i n g l e s l i p i n one g l i d e system) w i t h those o f <011> -deformed samoles ( 4 g l i d e systems e q u a l l y stressed) one f i n d s t h a t o n l y t h e low temoe- r a t u r e soectrum Si-K1 depends on t h e number and o r i e n - t a t i o n o f the a c t i v a t e d g l i d e systems /9/. Therefore t h e high-temperature c e n t r a l l i n e s show no d i r e c t connection w i t h t h e d i s l o c a t i o n s produced d u r i n g t h e deformation and w i l l be t r e a t e d l a t e r o n l y s h o r t l y .

z o i s o zoioo z m w - g - 2mso 20100 2 ~ 5 0 - 9 -

F i g . 1 : EPR spectra i n p l a s t i c a l l y deformed s i l i c o n a t r 1 1 T l

-

TM = 31K : D i s l o c a t i o n c e n t r e Si-K1

TM

= 145K : P o i n t d e f e c t centres.

The angular dependence o f t h e Si-K1 l i n e s c o u l d be explained by a S = 1/2- c e n t r e w i t h a n e a r l y a x i a l l y s y m e t r i c g-tensor o c c u r r i n g f o r every g l i d e

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979621

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C6- 102 JOURNAL D E PHYSIQUE

s y s t e n i n two o r i e n t a t i o n s w i t h no a x i s b e i n g l o w i n - dexed ( / 7 / , t a b l e I ) . F o r t h e g l i d e system ( 1 i 1 )

LO111

t h e 9,-axes l i e i n [ 1 ? 3 7 and E l 3 2 1 d i r e c - t i o n s w i t h an equal a n g l e o f 22" t o [I1111 resp.

C l l i 7 ,

t h e normals o f t h e g l i d e p l a n e P : (111) and t h e c r o s s g l i d e p l a n e 9 : (117). T h i s f i n d i n g a l r e a d y shows t h a t t h e S i - K 1 resonance e l e c t r o n s a r e l o c a t e d i n a t y p e o f d i s l o c a t i o n segments f o r which P and Q must o c c u r i n a symmetric manner.

hanced p c h a r a c t e r . The wave f u n c t i o n oarameters g i - ven i n t a b l e I 1 a r e c o n s i s t e n t w i t h t h o s e o f most o f t h e r a d i a t i o n induced d e f e c t c e n t r e s w i t h t h e r e s o - nance e l e c t r o n l o c a l i z e d i n a s i n g l e d a n g l i n g bond s t a t e /I/.

T a b l e I 1 : H y p e r f i n e i n t e r a c t i o n t e n s o r o f S i - K 1 H y p e r f i n e i n t e r a c t i o n t e n s o r o f S i - K 1

T a b l e I : g - t e n s o r o f S i - K 1 g l - a x i s [ 1 2 3 1

I1321

g - t e n s o r of S i - K 1

a2:

f r a c t i o n a l a m o u n t o f s c h a r a c t e r

P Z :

f r a c t i o n a l a m o u n t o f p c h a r a c t e r

y 2 : f r a c t i o n a l a m o u n t o f t h e t o t a l w a v e f u n c t i o n Orientatic'ns/

o f l i n e 2

(1,231

1

^[5,73]

^bfl211

^9,22"^{f r o m}

~ l l i i l

l o c a l i z e d a t this s i t e a n a l y s ~ s aftcr Watkins and Corbett.Phys. Rev aL.1359 (6L)

72 0 . 5 ~ 0.54 h f - a x i s

[ I i i i : P [ 1 1 i l : Q

The s t r o n g e s t i n s t r u m e n t f o r t h e develooment o f , A f t e r t h i s f i n d i n g one i s shure t h a t t h e c e n t r e n o d e l s f o r EPR c e n t r e s i s t h e knowledge of t h e hyper- r e s p o n s i b l e f o r S i - Y l i s symmetrical t o t h e two f i n e i n t e r a c t i o n s w i t h t h e n u c l e i a d j a c e n t t o t h e r e - { i l l } olanes whose l i n e of i n t e r s e c t i o n g i v e s t h e SOnanCe e l e c t r o n . I n t h e Case of s i l i c o n , o n l y S i - 2 9 B u r g e r s v e c t o r o f t h e d i s l o c a t i o n s . The o n l y k i n d o f w i t h a n a t u r a l abundance of 4.7 % has a n u c l e a r s p i n d i s l o c a t i o n s w h i c h a r e s y m n e t r i c t o p and Q a r e t h e

, (of 1/21 so t h a t f o r any a d j a c e n t s i t e t o t h e u n p a i r e d screw d i s l o c a t i o n s w h i c h f r o m t h e i r t o p o l o g y i n t h e e l e c t r o n one can e x p e c t a p a i r of h y p e r f i n e l i n e s undissociated state do not need anv broken bond. As w i t h a b o u t 1/40 o f t h e c e n t r a l l i n e s i n t e n s i t y . From we already know from weak beam that also the t h e a n g u l a r dependence of these l i n e s i t i s p o s s i b l e screw dislocations are split it seems to be mostly t o deduce t h e h y p e r f i n e i n t e r a c t i o n t e n s o r A w h i c h promising to look at the 30 -degree partial disloca- g i v e s i n s i g h t i n t h e amount and t h e c h a r a c t e r o f t h e

tions as origin o f the unpaired electron. As figure wave f u n c t i o n i n t e r a c t i n g w i t h t h a t nucleus.

shows t h e c o r e s o f t h e s e p a r t i a l d i s l o c a t i o n s c o n t a i n I n t h e case of t h e d i s l o c a t i o n c e n t r e s t h e s e

in the simple ball and wire model two bonds in the h y p e r f i n e l i n e s h i t h e r t o c o u l d n o t be d e t e c t e d because direction of (

c

^li12) ând ^{( [111i}⁷⁾ ândâ^planar

t h e s p x t r u m of t h e p e r i p h e r a l l i n e s i s j u s t a t t h e

configuration o f atoms, namely a,b,c,d. The fourth expected p o s i t i o n o f t h e h y p e r f i n e p a i r s .

e l e c t r o n a t atom b would be expected i n t h e s i m p l i e s t Very r e c e n t l y , however, we succeeded i n f i n d i n g

and a n a l y s i n g one s e t o f h y p e r f i n e s a t e l l i t e s f o r each o f t h e S i - k l l i n e s . T h i s was o n l y o o s s i b l e by t h e use o f p - S i w i t h a b o u t 1.3 x 1016 B/cm3 w h i c h i n t h e d a r k shows no p e r i p h e r a l l i n e s b u t s t i l l enough i n t e n - s i t y o f t h e S i - K 1 l i n e s . A d d i t i o n a l l y , spectrum accu- m u l a t i o n w i t h t h e a i d o f a computer has t o be used t o enhance t h e s i g n a l t o n o i s e r a t i o o f t h e s e v e r y weak l i n e s .

The r e s u l t s of t h e a n a l y s i s o f t h e h y p e r f i n e t e n s o r based on t h e wave f u n c t i o n parameters e v a l u a - t e d b y Watkins and C o r b e t t /11/ i s g i v e n i n t a b l e 11.

F o r b o t h l i n e s o f t h e Si;K1 c e n t r e a b o u t 60 % o f t h e wave f u n c t i o n i s l o c a l i z e d a t a s i n g l e s i l i c o n atom a x i a l l y symmetric t o t h e d i r e c t i o n s

P

( ~ l i l l ) and Q ( [ l l i ] , r e s o e c t i v e l y . The c h a r a c t e r o f t h e wave

-11 "1

IIO+~-~I

f u n c t i o n i s n e a r l y a s p 3 - h y b r i d o r b i t a l w i t h an en-

a2

0.12 0.12 1 2 5

125

case t o f o r m a r e a l d a n g l i n g bond i n t h e d i r e c t i o n o f t h e d i s l o c a t i o n l i n e w h i c h i s i n t h i s case [ O l l ] , t h e B u r g e r s v e c t o r of t h e u n d i s s o c i a t e d d i s l o c a t i o n . As t h e t h r e e n e i g h b o u r i n g atoms a,c,d, f o r m n e a r l y t h e b o n d i n g a n g l e s f o r an s p 2 - h y b r i d s t a t e :

a : = $(ab, c d )

- -

= 109.5'; B : =

$(a, x)

⁼ 109.5' ; y : = $(%,

a6)

= 141'

t h e d a n g l i n g bond s t a t e s h o u l d be a p - t y p e s t a t e . T h i s s t a t e w h i c h s h o u l d g i v e r i s e t o a h y p e r f i n e i n t e r a c - t i o n i n t h e C O l l l - d i r e c t i o n cannot b e r e s o o n s i b l e f o r t h e S i - K 1 c e n t r e b u t i t i s assumed t o produce t h e f i n e s t r u c t u r e l i n e s (Si-K2) w h i c h w i l l be d i s - cussed l a t e r .

A d a n g l i n g bond i n t h e d i r e c t i o n o f

P

o r Q can be produced i f one t a k e s away atom b and forms i n t h i s way t h e a l r e a d y d i s c u s s e d a s s o c i a t i o n o f a d i s -

P2

0.88 6.88 78

78

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E . Weber and H . Alexander ^C6-103

l o c a t i o n w i t h a s t a c k i n g f a u l t /12/.

F i g . 2 : Atomic s t r u c i u r e i n t h e d i s l o c a t i o n c o r e o f a 30" p a r t i a l d i s l o c a t i o n (bp = 1/6 [T12])

a) p u r e p a r t i a l d i s l o c a t i o n

b ) p a r t i a l w i t h a s s o c i a t e d v a c a n c y ; i n d i c a t e d a r e t h e d i r e c t i o n s o f t h e gl- and t h e h y p e r f i n e a x i s o f t h e d i s l o c a t i o n c e n t r e Si-K1.

I n t h i s case t h r e e d a n g l i n g bonds would r e a c h i n t o t h e d i s l o c a t i o n core, two o f which c o u l d f o r m a bon- d i n g s t a t e as has been observed i n many p o i n t d e f e c t s i n s i l i c o n (see F i g . 2). From t h e symmetry o f t h e c e n t r e ( a = B + y ) i t i s r e a s o n a b l e t o e x p e c t t h e dan- g l i n g bond a t t h e c - s i t e , whereas a and b s h o u l d f o r m t h e s u b s t i t u t i n g bond. The gl-axis i s i n t h i s case p e r p e n d i c u l a r t o t h e d i r e c t i o n

6a

w h i c h l e a d s i n t o t h e s t a c k i n g f a u l t . To remain i n t h i s p i c t u r e , t h e second l i n e o f t h e S i - K 1 c e n t r e cannot be formed i n t h e o t h e r p a r t i a l d i s l o c a t i o n on t h e g l i d e p l a n e w h i c h would a l s o g i v e a d a n g l i n g bond i n t h e P d i r e c - t i o n . T h e r e f o r e remains o n l y t h e s p l i t t i n g o f t h e screw d i s l o c a t i o n i n t h e c r o s s g l i d e p l a n e w h i c h would l e a d t o e x a c t l y t h e same s i t u a t i o n as f i g u r e 2 b u t now Q b e i n g t h e d a n g l i n g bond d i r e c t i o n . Such a s p l i t t i n g has a l r e a d y been observed by Gomez /13/, b u t up t o now no i n f o r m a t i o n e x i s t s upon t h e q u a n t i -

t a t i v e r e l a t i o n between t h e f r a c t i o n o f screw d i s l o - c a t i o n s s p l i t on P and Q. T h i s t e n t a t i v e model f o r t h e c e n t r e S i - K 1 o f c o u r s e needs f u r t h e r s u p p o r t es-

~ e c i a l l y i n c o n n e c t i o n w i t h weak beam TEM. A f i r s t p r e l i m i n a r y r e s u l t o f an EPR experiment w i t h a spe- cimen c o n t a i n i n g a b o u t 30% screw d i s l o c a t i o n s a f t e r a l o w temDerature d e f o r m a t i o n under h i g h s t r e s s /I41 shows t h e i n t e n s i t y o f t h e EPR d i s l o c a t i o n s p e c t r a beeing p r o ~ o r t i o n a l t o t h e screw d i s l o c a t i o n d e n s i t y . 3. P e r i p h e r a l l i n e s : Si-K2.- Besides t h e c e n t r a l l i n e s (due t o c e n t r e s w i t h s p i n S = 1 / 2 ) p l a s t i c d e f o r m a t i o n o f s i l i c o n produces a l s o a u n i q u e f i n e s t r u c t u r e spectrum (Si-K2) c o n s i s t i n g o f a t l e a s t 12 l i n e s on b o t h s i d e s o f t h e c e n t r a l spectrum (/6/,/7/, / l o / ) . U s i n g a g a i n c r y s t a l s w i t h d i f f e r e n t deforma- t i o n a x i s i t c o u l d b e shown t h a t each a c t i v a t e d g l i d e system produces one s e t o f ~ e r i p h e r a l li n e s w i t h t h e Burgers v e c t o r o f t h a t g l i d e system as a x i s o f t h e s p l i t t i n g t e n s o r . I m p u r i t y atoms as o r i g i n o f t h i s 5 > 1 / 2 c e n t r e c o u l d b y f a r be r u l e d o u t u s i n g Neutron A c t i v a t i o n A n a l y s i s /16/, so t h a t t h i s c e n t r e must come f r o m u n p a i r e d e l e c t r o n s i n t h e d i s l o c a t i o n c o r e c o u p l e d t o g e t h e r t o f o r m an e f f e c t i v e s p i n S > 1/2 w i t h t h e B u r g e r s v e c t o r o f t h e ( p e r f e c t ! ) d i s l o c a - t i o n as most i m o o r t a n t a x i s o f t h e c o u p l i n g t e n s o r . As o r i g i n o f t h i s c o u p l i n g some d i f f e r e n t models a r e d i s c u s s e d :

-

The spectrum can be d e s c r i b e d b y groups o f up t o 4 e l e c t r o n s w i t h a Hubbard-type H a m i l t o n i a n t a k i n g i n t o a c c o u n t hooping o f t h e e l e c t r o n s a l o n g t h e d i s l o c a t i o n l i n e (D. N i e m i e t z andH.D. D i e t z e , un- p u b l i s h e d ) . I t s a n i s o t r o o y must t h e n be d e s c r i b e d b y a c r y s t a l f i e l d i n t e r a c t i o n w i t h t h e B u r g e r s v e c t o r o f t h e d i s l o c a t i o n as main a x i s .

-

^Asecond e x p l a n a t i o n assumes c o u p l i n g between t h e u n p a i r e d s p i n s b y t h e f o r m a t i o n of magnetic p o l a - r o n s /16/.

R.M; W h i t e and

J.F.

Gouyet /17/ c a l c u l a t e d t h e exchange i n t e r a c t i o n o f two d a n g l i n g bonds i n a S i 2 H 6 c l u s t e r and f o u n d an a n t i f e r r o m a g n e t i c g r o u r d s t a t e s e p e r a t e d 6 meV f r o m t h e t r i p l e t s t a t e . The spectrum w i t h i t s a n i s o t r o p y i s e x p l a i n e d by t h e c o u p l i n g o f f i n i t e s o i n c h a i n s (up t o e i g h t s p i n s a r e c o n s i d e r e d ) a g a i n i n a c r y s t a l l i n e e l e c t r i c f i e l d w i t h t h e Burgers v e c t o r as main d i s t o r t i o n a x i s .

T. Wosinski and T. F i g i e l s k i / I S / e x p l a i n t h e i r r e s u l t s of s p i n dependent r e c o m b i n a t i o n experiments w i t h deformed s i l i c o n b y l i m i t e d segments o f cou- p l e d s p i n s a l o n g t h e d i s l o c a t i o n l i n e . T h e i r c a l -

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c u l a t i o n o f t h e exchange i n t e g r a l between two sp3 o r b i t a l s d a n g l i n g p e r p e n d i c u l a r t o t h e d i s l o c a - t i o n a x i s l e a d s t o a p o s i t i v e v a l u e o f 85 meV and t h e r e f o r e t o a f e r r o m a g n e t i c ground s t a t e .

L. B a r t e l s e n

/ l o /

o f o u r group e x p l a i n e d t h e ex- p e r i m e n t a l l y found l i n e p o s i t i o n s by chains o f up t o f i v e exchange c o u p l e d s p i n s i n t h e d i s l o c a t i o n core. He c o u l d d i s t i n g u i s h between two groups of l i n e s ( " 2 3 K " l i n e s and "50 K " l i n e s ) measurable a t d i f f e r e n t temperatures. From t h e l i n e s p r e s e n t a t l o w e s t temperatures he concluded t h a t t h e cou- p l in g must b e o f f e r r o m a g n e t i c t y p e . The coup1 i n g c o n s t a n t c o u l d o n l y be e s t i m a t e d r o u g h l y t o about

Fig. : Schemati> of the overlaDping pz-orbitals 12 meV. The assignment o f c e r t a i n o a i r s o f l i n e s a l o n g a 30" d i s l o c a t i o n . L i m i t s f o r t h e c h a i n s t o a p a r t i c u l a r number o f c o u p l i n g e l e c t r o n s i s c o u l d be e.g. i o n i z e d atoms w i t h o u t p z e l e c t r o n . s u p p o r t e d by a n n e a l i n g e x p e r i m e n t s (D.Bresgen, 4. Photoresponse o f t h e d i s l o c a t i o n s p e c t r a . - F u r t h e r u n p u b l i s h e d ) w h i c h show t h a t t h e l i n e s b e l o n g i n g i n s i g h t i n t h e n a t u r e o f t h e d i s l o c a t i o n s p e c t r a can t o l o n g c h a i n s ( n = 4.5) anneal a t l o w e r tempe- be g a i n e d f r o m t h e i r dependence on t h e sample i l l u m i - r a t u r e s t h a n t h e s h o r t c h a i n ( n = 2.3) l i n e s . n a t i o n d u r i n g t h e EPR measurement (see F i g . 4) which

A l l t h e models d e s c r i b e d s h o r t l y s u p p o r t t h e has been i n v e s t i g a t e d by R. Erdmann i n o u r l a b . i d e a o f some k i n d o f c o u p l i n g o f u n p a i r e d s p i n s i n A f t e r c o o l i n g down an undoped sample i n t h e t h e d i s l o c a t i o n c o r e whereas t h e n a t u r e and t h e quan- d a r k an i l l u m i n a t i o n w i t h band gap l i g h t (hv ^.\.1.2 eV) t i t a t i v e d e t a i l s o f t h i s c o u p l i n g s t i l l need f u r t h e r . r e s u l t s i n an i n c r e a s e o f t h e p e r i p h e r a l l i n e s where- e x a m i n a t i o n . A l l t h e s e models b r i n g no new i n f o r m a - as t h e c e n t r a l l i n e s decrease i n i n t e n s i t y . An e f f e c t t i o n f o r t h e q u e s t i o n where t h e c o u p l e d s p i n c e n t r e s

a r e l o c a t e d . An i n s p e c t i o n o f t h e g - t e n s o r and D-ten- s o r o f t h i s c e n t r e (/7/,/10/) shows t h e B u r g e r s vec- t o r o f t h e d i s l o c a t i o n s as t h e o n l y i m p o r t a n t d i r e c - t i o n . T h i s p o i n t s t o t h e screw d i s l o c a t i o n j u s t as i n t h e case o f t h e S i - K 1 c e n t r e .

F i g u r e 2 shows t h a t i n t h e 30" p a r t i a l d i s l o c a - , t i o n a t atom b an u n p a i r e d e l e c t r o n can be l o c a t e d i n a n e a r l y p e r f e c t p - o r b i t a l . These u n p a i r e d e l e c -

coming j u s t from a change of t h e c o n d u c t i v i t y o f t h e sample ( Q - f a c t o r o f t h e c a v i t y ) i s e l i m i n a t e d b y simul- taneous measurement o f a s t a n d a r d sample.

Once t h e i l l u m i n a t e d s t a t e i s a c h i e v e d a t low t e m p e r a t u r e i t needs h o u r s i n t h e d a r k t o come back t o t h e " d a r k spectrum". Warming up t h e p r e v i o u s l y i l l u m i n a t e d sample i n t h e d a r k t o room t e m p e r a t u r e w i t h subsequent c o o l i n g down l e a d s however t o an a n n e a l i n g o f t h e ill u m i n a t i o n e f f e c t .

t r o n s s h o u l d have a c o n s i d e r a b l e o v e r l a p a l o n g t h e The photon energy dependence o f t h e d i s l o c a t i o n d i s l o c a t i o n l i n e C 0 1 1 ] as i n d i c a t e d i n f i g u r e 3, c e n t r e ' s photoresponse i s g i v e n i n f i g u r e 5 by t h e and we t h e r e f o r e assuae t h a t t h e s e e l e c t r o n s form i n t e n s i t y o f one o f t h e p e r i p h e r a l l i n e s .

t h e Si-KE c e n t r e .

line

Central lines (Si

-

K 1 ) Peripheral lines ( S i - K 2 )

F i g . 4 : C e n t r a l l i n e s (Si-K1) and p e r i p h e r a l l i n e s (Si-K2) o f an undoped sample measured i n t h e d a r k ( 0 )

and d u r i n g band gap i l l u m i n a t i o n (+) (H - p a r a l l e l [ l l i l ) .

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E . Weber and H. Alexander C6-105

I t i s c l e a r l y t o be seen t h a t the i l l u m i n a t i o n e f f e c t can a l s o be achieved by photons w i t h an energy o f about 0.68 eV. I n t h e case o f t h e c e n t r a l l i n e s t h i s k i n d o f i l l u m i n a t i o n leads t o a decrease i n i n t e n s i t y j u s t as d i d the band gap l i g h t .

Fig. 5 : Photon energy dependence o f t h e Si-K2 spectrum measured by t h e i n t e n s i t y o f one p e r i p h e r a l l i n e d u r i n g i l ~ l u m i n a t i o n , s t a r t i n g a t low energies.

I n p-Si w i t h about 1016B/cm3 t h e behaviour i s d i f f e r e n t . . I n t h e dark t h e p e r i p h e r a l l i n e s cannot be observed a t a l l whereas the Si-K1 l i n e s a r e weaker than i n undoped m a t e r i a l . I l l u m i n a t i o n leads now t o an enhancement o f b o t h d i s l o c a t i o n spectra. I n addi- t i o n , t h e EPR s p e c t r a o f boron i n deformed samples (N. G e l l r i c h , unpubl i s h e d ) a l s o increase i n i n t e n s i t y . T h i s enhancement i s again achieved by band gap l i g h t as w e l l as by 0.68 eV l i g h t .

From these f i n d i n g s we conclude t h a t d u r i n g t h e i l l u m i n a t i o n e l e c t r o n s are e x c i t e d from t h e valence band o r t h e i o n i z e d shallow acceptors i n t o d i s l o c a - t i o n l e v e l s l o c a t e d 0.68 eV c 0.05 eV above the va- lence band. T h i s process can be made v i a t h e conduc- t i o n band (band gap l i g h t ) o r d i r e c t l y w i t h t h e 0.68 eV photons. The decrease o f t h e Si-K1 c e n t r e i n t h e undoped sample should come from t h e p o p u l a t i o n o f dangling bonds w i t h a second e l e c t r o n thus p a i r i n g o f f t h e s p i n whereas t h e increase of t h e coupled

-

s p i n c e n t r e Si-K2 i n d i c a t e s t h a t a d d i t i o n a l e l e c t r o n s favour coupling, perhaps by the f o r m a t i o n of magnetic p o l arons /16/.

I n p-Si b o t h k i n d s o f EPR a c t i v e d i s l o c a t i o n s t a t e s are emptied by t h e chemical acceptors, so t h a t o n l y a p a r t o f t h e s i n g l e dangling bond s t a t e s remains. Mow i l l u m i n a t i o n repopulates b o t h types of centres and leads t o an increase o f t h e number o f n e u t r a l Boron atoms.

I t w i l l be i n t e r e s t i n g t o compare these r e s u l t s w i t h t h e l e v e l s found by e l e c t r i c a l methods, a t b e s t by f u r t h e r experiments w i t h d i f f e r e n t methods i n c l u - d i n g EPR a t t h e same samples.

5. P o i n t d e f e c t s p e c t r a Si-K3

-

Si-K5.- Measuring t h e spectra a t h i g h e r temperatures (TM >60K) new c e n t r a l l i n e s emerge which must be a t t r i b u t e d t o p o i n t d e f e c t c l u s t e r s o f t h e vacancy type produced d u r i n g t h e deformation /9/. Some o f these spectra can be recorded already a t 40K when measuring i n d i s p e r s i o n and thus a v o i d i n g s a t u r a t i o n o f the spectra. J u s t i n t h e tem- p e r a t u r e range o f 40

-

50K S.V. Broude e t a1

.

/8/

c l a i m t o f i n d a magnetic phase t r a n s i t i o n i n t h e d i s - l o c a t i o n centres. T h i s t r a n s i t i o n i s i n view of our r e s u l t s e x p l a i n e d q u a n t i t a t i v e l y by changing from t h e d i s l o c a t i o n spectrum Si-K1 t o t h e p o i n t d e f e c t spec- t r a .

Annealing o f these centres takes p l a c e around 700°C, i . e . i n t h e same temperature range as t h e annealing o f t h e d i s l o c a t i o n centres.

C u t t i n g processes as o r i g i n o f t h e p o i n t defects, which amount about 10' defects/cm3 i n th e deformed samples, c o u l d be r u l e d o u t so t h a t these p o i n t d e f e c t s are most l i k e l y produced by changes i n t h e core s t r u c t u r e o f moving p a r t i a l d i s l o c a t i o n s ( / 9 / , /12/) connected w i t h the t r a n s i t i o n from t h e associa- t i o n s t a t e t o t h e pure s p l i t s t a t e .

E l e c t r i c a l measurements o f deformed s i 1 ic o n /19/

and germanium /20/ a l s o f i n d evidence f o r t h e forma- t i o n o f e l e c t r i c a l l y a c t i v e p o i n t d e f e c t s d u r i n g deformation a t r a t h e r low temperatures.

6. Conclusion.- The EPR measurements o f deformed s i - l i c o n a l l o w some important conclusions which can be summarized as f o l l o w s :

-

A f t e r deformation a t n o t too h i g h temperature e x i s t s t r o n g l y l o c a l i z e d dangling bond s t a t e s which count D a r t o f a percent o f t h e t o t a l number o f atoms i n d i s l o c a t i o n cores. Yost o f t h e remaining ( t o p o l o - g i c a l l y p o s s i b l e ) dangling bonds a r e o b v i o u s l y rearranged forming extended s u b s t i t u t i n g bonds.

-

The EPR spectrum o f these l o c a l i z e d spins has a h y p e r f i n e s t r u c t u r e which leads us t o t h e cores of 30" p a r t i a l of screw d i s l o c a t i o n s as places o f these unpaired e l e c t r o n s . Perhaps t r a p p i n g o f a vacancy i s needed t o form t h e Si-K1 centre.

-

There e x i s t 1 i m i te d d i s l o c a t i o n segments again l o - cated i n t h e 30" p a r t i a l s of screw d i s l o c a t i o n s along which unpaired e l e c t r o n s couple together. The number o f these e l e c t r o n s i s a l i t t l e more than t h e number o f s i n g l e dangling bonds.

These centres a r e supposed t o lay an important r o l e i n t h e s p i n dependent recombination processes /18/. The most probable o r i g i n o f t h e corresponding EPR Spectrum Si-K2 are o v e r l a p p i n g p-type o r b i t a l s along screw d i s l o c a t i o n s .

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C6-106 JOURNAL DE PHYSIQUE

I l l u m i n a t i o n o f t h e c r y s t a l d u r i n g t h e measurement r e s u l t s i n an enhancement o f t h e number o f coupled s p i n c e n t r e s whereas t h e s i n g l e d a n g l i n g bond cen- t r e s decrease. T h i s e f f e c t i s achieved by band gap l i g h t and by photons o f 0.68 eV energy. I t i s ex- p l a i n e d by t h e e x c i t a t i o n o f e l e c t r o n s f r o m t h e valence band o r i o n i z e d s h a l l o w a c c e p t o r s t o t h e EPR a c t i v e d i s l o c a t i o n s t a t e a t Ev

+

0.68 eV

'

0.05 eV.

Low temperature d e f o r m a t i o n produces i n a d d i t i o n p o i n t d e f e c t c l u s t e r s w i t h d a n g l i n g bond e l e c t r o n s .

/14/ Wessel, K. and Alexander, ti., P h i l o s . Mag.

35

(1977) 1523.

/15/ R i o t t e , H.G., Herpers, U. and Weber, E., Radio- chem. Radioanal. L e t t .

-

30 (1977) 311.

/ 161 L e p i ne

,

D.

,

Grazhul i s

,

V. A. and Kapl an, D.

,

Proc. 1 3 t h I n t . Conf. Phys. Semicond., Rome (1976) 1081, J.F. Gouyet a t t h i s conference.

/17/ Y h i t e , R.M. and Gouyet, J.F., Phys: Rev.

B16

(1977) 3596.

/18/ d o s i n s k i , T. and F i g i e l s k i , T., Phys. S t a t u s S o l i d i ( b ) - 83 (1977) 93.

/19/ K i m e r l i n g , L.C. and P a t e l , J.R., J. Physique C o l l o q .

40

(1979) t h i s issue.

These vacancy - t y p e c l u s t e r s a r e o f e x t r a o r d i n a r y /20/ A l b e r s , M., G a b r i e l , A. and S c h r t i t e r , W . , Inst:

thermal s t a b i l i t y compared w i t h r a d i a t i o n induced Phys. Conf. Ser.

31

(1977) 509.

p o i n t d e f e c t s . They anneal a t about t h e same tempe- r a t u r e as t h e paramagnetic d i s l o c a t i o n c e n t r e s .

Acknowledgements.- We want t o thank P r o f . H.D. D i e t z e f o r u s e f u l d i s c u s s i o n s . Our coworkers D i p l . Phys.

R. Erdmann, N. G e l l r i c h , D. Bresgen and K.H. KUsters a r e k i n d l y acknowledged f o r l e a v i n g o f u n p u b l i s h e d r e s u l t s . The Deutsche Forschungsgemeinschaft suppor- t e d t h e work by f i n a n c i a l a i d . We w i s h t o thank a l s o Hrs. G. Schemmann f o r her he1 p c a r e f u l l y p r e p a r i n g

t h e samples.

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