DEEP LEVEL DEFECTS IN PLASTICALLY DEFORMED SILICON

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DEEP LEVEL DEFECTS IN PLASTICALLY DEFORMED SILICON

E. Weber, H. Alexander

To cite this version:

E. Weber, H. Alexander. DEEP LEVEL DEFECTS IN PLASTICALLY DEFORMED SILICON.

Journal de Physique Colloques, 1983, 44 (C4), pp.C4-319-C4-328. �10.1051/jphyscol:1983438�. �jpa- 00223057�

JOURNAL DE PHYSIQUE

Colloque C4, supplément au n°9, Tome 44, septembre 1983 page C4-319

D E E P LEVEL D E F E C T S IN P L A S T I C A L L Y D E F O R M E D SILICON E.R. Weber and H. Alexander

Depart, of Solid State Physios, University of Lund, Box 725, S-220 07 Lund, Sweden

RESUME. - La déformation p l a s t i q u e du s i l i c i u m engendre l a f o r m a t i o n d'amas de d i s l o c a t i o n s e t de défauts ponctuels de d i f f é r e n t e s s o r t e s . Ces défauts peuvent ê t r e électriquement a c t i f s , e t créer des niveaux d ' é n e r g i e profonds.

Les mesures de RPE permettent de déterminer l a symétrie des centres para- magnétiques i n t r o d u i t s par d é f o r m a t i o n , e t donc d ' é t a b l i r une d i s t i n c t i o n e n t r e l e s spectres associés aux d i s l o c a t i o n s e t aux défauts p o n c t u e l s . Les spectres de DLTS e t de photo-luminescence peuvent ê t r e c o r r é l é s avec des défauts s p é c i f i q u e s c a r a c t é r i s é s en RPE, pour d i f f é r e n t s é c h a n t i l l o n s déformés. Ces r é s u l t a t s permettent de t i r e r l e s conclusions sur l a nature e t l e s c o n d i t i o n s de f o r m a t i o n des défauts p o n c t u e l s , e t sur l e s défauts électriquement a c t i f s réellement associés aux d i s l o c a t i o n s dans l e s i l i c i u m . ABSTRACT.- Plastic deformation of silicon results in the formation

of dislocations and point defect clusters of various kinds. These defects can be electrically active, forming deep energy levels. EPR experiments allow to determine the symmetry of deformation induced paramagnetic centers and thus a distinction between dislocation- and point defect related spectra. DLTS and photo-luminescence spectra can be correlated with specific defects characterized by EPR, using variously deformed samples. These results allow to draw conclusions on the nature and formation conditions of point defects and truly dislocation-related electrically active defects in silicon.

1. INTRODUCTION

During plastic deformation of silicon dislocations and point defects are produced, introducing energy levels deep in the gap, which drastically change the electrical properties of deformed crystals. Investigations of these deep level defects were frequently performed in the past by using quite unspecific methods like Hall effect measurements. Based on the results of such experiments, model calculations of the electrical properties of dislocations were carried out, yet hardly could elucidate the micAoicopZc naJufie. of these deformation induced defects. Yet Electron Para- magnetic Resonance (EPR) experiments can, among others, directly give information on the symmetry of defects containing an unpaired electron. In this work shall be tried to combine the results of recent electrical and optical investigations of deep level defects in plastically deformed silicon with the information obtained from EPR experiments, using crystals with well-defined dislocation structures /!/.

2. EPR OF PLASTICALLY DEFORMED SILICON

EPR experiments with plastically deformed silicon have been described up to now by three groups, see /1-4/ and references therein. The spectra investigated are compiled in Table 1, typical average spin concentrations for three characteristic deformation conditions are given in Table 2.

Permanent address: Abtlg. f. Metallphysik, II. Phys. Inst., Univ. Koln, D5000 Koln 41, F.R.G.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983438

C4-320 JOURNAL DE PHYSIQUE TABLE 1: EPR CENTERS I N DEFOR?QED SILICON

Line-

Spectrum Spin w i d t h Model References

(Gauss) broad 1 i ne

1 /2

-

" y " , " D I' v a r i o u s surroundings /I ,3,4,7,9/

Si-Kl 1 /2 1.3 s i n g l e dbs i n t h e d i s l o c a t i o n core /1,2,4,6,10/

Si-K2 21 -1 0 e x c i t e d s t a t e o f coupled Si-K1 dbs

Si-K3 1 / 2 1 .O

S i -K4 1 /2 1.0 p o i n t d e f e c t c l u s t e r s

Si-K5 1/2 1 .O

Si-K6 1 / 2 -100 B a t d i s l o c a t i o n s /14,15/

Si-K7 1/2 1.2 P a t d i s l o c a t i o n s /16/

Tab1 e 2: EPR SPIN CONCENTRATIONS

- - - - - - - - -

deformation 650°c, 2 = 30MPa 8 5 0 ~ / 4 2 0 ~ ~ , r = 300MPa d i s l o c a t i o n

d e n s i t y

=.sites i n t h e

d i s l o c a t i o n core 3 x 2 x 1017 6 x l 0 l 4 [ ~ m - ~ ] ( 2 p a r t i a l s )

Si-Kl/K2 8 x l 0 l 3 4 x lo14 < l o 11 [ cm-3 I

Si-K3-K5 I 4 < 10 11 _[ cm-3 1

broad l i n e

- 6 x l 0 l 4 - 4 x 1 0 15 < 10 12

"Y","DM ^[ I

( t y p i c a l values f o r FZ s i l i c o n , deformed by s t a t i c compression along [2131 )

%An inhomogeneously broadened, asymmetric l i n e ( c a l l e d Si-Y i n /4/) o f about 7G w i d t h near g=2.005 corresponds t o t h e l a r g e s t number o f unpaired e l e c t r o n s . The i n v e s t i g a t i o n s o f t h e "D-center" by Grazhulis e t a l . /3,5,8/ were i n f a c t m a i n l y concerned w i t h t h i s l i n e , as t h e narrow " f i n e s t r u c t u r e l i n e s " (Si-K1 spectrum, see 2.2) c o n t a i n a t l e a s t an order o f magnitude l e s s spins. T h i s broad l i n e shows o n l y a weak response t o i l l u m i n a t i o n : i n undoped s i l i c o n i t s i n t e n s i t y increases upon i l l u m i n a t i o n by a few percent /5/, i n c o n t r a s t t o t h e marked decrease o f Si-K1 by about 70% / 6 / . A n o t i c e a b l e g-value a n i s o t r o p y i n d i c a t e s a c o r r e l a t i o n w i t h t h e d i s l o c a t i s n s introduced. A small f r a c t i o n o f t h i s l i n e i s even t h e r m a l l y s t a b l e above 800 C /7,8/.

Whereas Grazhulis e t a l . /3/ t r y t o e x p l a i n t h i s l i n e as a r i s i n g from d a n g l i n g bonds i n t h e c o r e o f unreconstructed d i s l o c a t i o n s , t h e present authors favour t o a s c r i b e t h i s l i n e t o p o i n t d e f e c t s near t h e d i s l o c a t i o n s . Such d e f e c t s experience v a r i o u s s t r a i n f i e l d s , according t o t h e i r r e s p e c t i v e l a t t i c e s i t e , r e s u l t i n g i n an inhomo- geneously broadened l i n e . The observation o f s a t u r a t i o n o f j u s t a small, narrow p a r t o f t h i s l i n e ( " h o l e burningU/9/) supports t h i s p i c t u r e o f s p a t i a l l y seperated p o i n t defects.

Fig. 1: EPR spectra o f p l a s t i c a l l y deformed (650'~) s i l i c o n a t ~ / / [ 1 1 T ] . The 1 ow temperature spectra (Si-K1 ) a r e markedly d i f f e r e n t f o r t h e two deformation axes whereas t h e h i g h temperature spectra (Si-K3-K5) a r e almost i d e n t i c a l /2/,

2.2. Superimposed on t h i s broad l i n e i s a spectrum o f o r i e n t a t i o n dependend, narrow Fi35nance l i n e s Si-K1, F i g . 1 /2/. Analysis o f t h e Si-K1 o r i e n t a t i o n dependence revealed g-tensors unique f o r EPR c e n t e r s i n s i l i c o n : f o r each a c t i v a t e d g l i d e system 2 o u t o f 24 e q u i v a l e n t g-tensor o r i e n t a t i o n s a r e detected. The h y p e r f i n e s a t e l l i t e s a r i s i n g from Si-29 (4.9% abundance) proved Si-K1 t o be a t y p i c a l "dangling bond" center i n s i l a c o n , t h e g-tensor axes and the h y p e r f i n e t e n s o r axes being t i l t e d by 22' and 6 , r e s p e c t i v e l y , from those two < I l l > - d i r e c t i o n s , which a r e perpendicular t o t h e Burgers v e c t o r o f t h e d i s l o c a t i o n s /2,18/. U n i a x i a l s t r e s s experiments demonstrated t h e p o s s i b i l i t y o f r e v e r s i b l e alignement even a t 1.4K /1,10/.

Thus the Si-K1 e l e c t r o n s must be a b l e t o hop between these two dangling bond s i t e s . The c o n c e n t r a t i o n o f t h i s d e f e c t corresponds o n l y t o a small f r a c t i o n o f t h e number o f l a t t i c e s i t e s i n t h e d i s l o c a t i o n core, Table 1.

Photo-EPR experiments showed t h a t a f u r t h e r spectrum, Si-K2, c o n s i s t i n g of coupled s p i n s o f S>1/2, i s c l o s e l y r e l a t e d w i t h Si-K1 ( F i g . 2 ) : I l l u m i n a t i o n w i t h 0.6 eV l i g h t , as w e l l as w i t h band-gap l i g h t , transforms S=1/2 d e f e c t s (Si-K1) i n t o Si-K2, i n d i c a t i v e f o r t h e capture o f an a d d i t i o n a l e l e c t r o n o n t o Si-K1 defects /6/.

Fig. 2:

EPR i n t e n s i t y o f Si-K1 (+) and Si-K2 ( a ) spectra

vs, i l l u m i n a t i o n wavelength /6/.

0 05 10 I. 5 2.0

hv(eV)

-

Si-K2 i s o n l y measurable a t temperatures above -5K, independent o f t h e microwave power used. This i n d i c a t e s t h a t Si-K2 m i g h t be an e x c i t e d t r i p l e t s t a t e , t h e ground s t a t e being a s p i n l e s s s i n g l e t . Fig. 3 shows t h e temperature dependence o f t h e Si-K2 i n t e n s i t y , being w e l l described by an Arrhenjus law f o r low temperatures, t h e slope corresponding t o the s i n g l e t - t r i p l e t s p l i t t i n g of 2.35meV. T h i s value i s i n t h e same o r d e r o f magnitude as t h a t found f o r t h e Si-I1 spectrum (9meV) ascribed t o t h e n e u t r a l divacancy /I]/. (That model has been r e c e n t l y questioned /12/).

JOURNAL DE PHYSIQUE

Temperature ( K )

looc ⁵⁰ , , , , ^{10 I I I} I ⁵

F i g . 3:

Temperature dependence o f Si-K2 EPR i n t e n s i t y . The slope o f t h e low temperature p a r t corresponds f o r b o t h microwave powers t o 2.35 meV.

Existence o f a t h i r d , s p i q l e s s charge s t a t e o f the Si-Kl/K2 d e f e c t i s obvious from t h e rnea&urernents of deformed p-Si: a f t e r c o o l i n g down i n t h e dark n e i t h e r Si-K1 n o r Si-K2 appear, b u t can be produced by i l l u m i n a t i o n w i t h midgap o r band-gap l i g h t /6/.

Summarizing, a l l r e s u l t s on Si-K1/K2 can be explained by a d e f e c t w i t h two dangling bond s i t e s , appearing e i t h e r b o t h empty, o r occupied w i t h one o r two e l e c t r o n s . The m u l t i p l i c i t y o f Si-K2 l i n e s shows, t h a t t h i s d e f e c t occurs i n several, s l i g h t l y d i f f e r e n t c o n f i g u r a t i o n s , such as e.g. unreconstructed j o g s o f d i f f e r e n t length.

The Si-Kl/K2 d e f e c t i s u n s t a b l e upon annealing a t about 800'~.

2.3. F u r t h e r deformation p ~ ~ d u c e d EPR spectra (Si-K3-K5) a r e measurable o n l y a t m e r temperature, F i g . 7 , They occur i n a l l c r y s t a l l o g r a p h i c a l l y e q u i v a l e n t

o r i e n t a t i o n s (12 f o r Si-K3 and Si-K4, 4 f o r Si-K5), n o t r e v e a l i n g any 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 present. Thus t h e y have been a s c r i b e d t o deformation induced p o i n t d e f e c t c l u s t e r s /13/. T h e i r f o r m a t i o n d u r i n g p l a s t i c deformation and annealing i s v e r y s i m i l a r t o t h e d i s l o c a t i o n - r e l a t e d Si-Kl/K2 d e f e c t .

2.4. I n a d d i t i o n t o these spectra, f o r which no r e l a t i o n t o i m p u r i t i e s c o u l d be found, i n B and P doped s i l i c o n f u r t h e r c h a r a c t e r i s t i c EPR s i g n a l s (Si-K6 /14,15/

and Si-K7 /16/) can be found. S i m i l a r as Si-Kl/K2 they do n o t appear i n a l l c r y s t a l l o - g r a p h i c a l l y e q u i v a l e n t o r i e n t a t i o n s , showing a c l o s e r e l a t i o n t o t h e d i s l o c a t i o n s present. T h e i r s t r o n g l y a n i s o t r o p i c g-tensors i n d i c a t e t h e shallow doping atoms themselves a t t h e d i s l o c a t i o n core t o be t h e most probable defect model.

2.5. Recently, t h e r e s ~ l t s obtained f ~ o m EPR spectra o f c r y s h a l s geformed w i t h h i g h

- s t r e s s (300MPa) a t 420 C ( a f t e r a 850 C predeformation, "850 /420 -samplesu) allowed t o draw a d d i t i o n a l conclusions on t h e n a t u r e o f a l l these EPR centers, see Table 2: lilhereas i n undoped s i l i c o n no EPR n i g n d can be hound, i n p- and n-Si o n l y Si-K6 o r Si-K7, r e s p e c t i v e l y , a r e w e l l detectableb T h i s shows t h a t t h e s t r a i g h t ,

<llO>-oriented d i s l o c a t i o n s present a f t e r t h e 420 C h i g h - s t r e s s deformation /17/

do n o t c o n t a i n any measurable d a n g l i n g bond e l & c t r ~ n s , ~ T h u s r e c o n s t r u c t i o n of t h e d i s l o c a t i o n core i s d i r e c t l y proven f o r t h e 30 and 90 p a r t i a l d i s l o c a t i o n s occuring predominantly i n these samples. Even r e l a x a t i o n o f t h e d i s l o c a t i o n s t r u c t u r e a t 390% (see chapter 4) does n o t produce EPR centers. However, i f i n t r i n s i c paramag- n e t i c c e n t e r s (2.1. -3.) have been introduced d u r i n g t h e predeformation, e.g. a t 650°c, they s u r v i v e the h i g h - s t r e s s deformation i n approximately constant c o n c e n t r a t i o n /18/.

3. OLTS OF PLASTICALLY DEFORMED SILICON

I n deep l e v e l t r a n s i e n t ~ p e c t r o s c o p y (DLTS), t h e f i l l i n g and t h e r m a l l y e x c i t e d emptying o f deep t r a p s i n t h e d e p l e t i o n r e g i o n o f a Schottky diode o r p / n - j u n c t i o n i s measured, u s u a l l y by means o f t h e t r a n s i e n t c a p a c i t y change a f t e r a m i n o r i t y o r m a j o r i t y c a r r i e r p u l s e /19/. T h i s extremely s e n s i t i v e technique i s d e f e c t - s p e c i f i c .

c a p t u r e process' i s determined by t h e e x i s t - Fig' 4: DLTS spectra Of p l a s t i c a l l y ence of a Coulomb b a r r i e r around charged, aeformed n-Si. For a l l s p e c t r a , a extended d e f e c t s 1 i ke d i s l o c a t i o n s , a s

boxcar system was used w i t h a l r e a d y discussed f o r t h e decay of photo- 123s- r a t e window ( t / t -4), t h e c o n d u c t i v i t y i n deformed S i and Ge /27/ and

bias Was ^{4 V 9} a i l l y n g pulse f o r t h e Si-Kl/K2 transformation /1,28/. Thus duration lomsec, OVpulse. most 1 i kelv a l l t h e s e deep l e v e l d e f e c t s a r e

I t y i e l d s f o r each d e f e c t a c h a r a c t e r i s t i c

" f i n g e r p r i n t " ( s e e below). Results of DLTS experiments with p l a s t i c a l l y deformed s i l i c o n have been f i r s t reported by Kimerling and Pate1 /20/. Subsequently, several f u r t h e r

. papers on t h i s s u b j e c t were published, e.g.

/21-25/, most work up t o now concentrating on n-Si.

Located at-dinlocaLLovrcl. he formation and

- annealing c o n d i t i o n s allow t o d i s t i n g u i s h

t h r e e d i f f e r e n t kinds of t r a p s i n n-Si:

n-si 3.1. An unusual broad l i n e E(.4) appears i n

1 x 1 0 ' ~ p/cm3 T n - S i samples containing d i s l o c a t i o n s .

-

(high stress)

C 800 C. I t i s measured i s o l a t e d a t best i n

-

-

200 300 /20/. The p r o p e r t i e s of t h i s l i n e a r e

Temperature ( K ) discussed in d e t a i l i n another paper of t h i s volume /29/. A s i m i l a r , thermally s t a b l e , Fig. 5: DLTS spectrum of 850°/4200~ d i s l o c a t i o n - r e l a t e d band H(.35) is found in high s t r e s s deformed n-Si. The deformed p-Si /20/. The e x a c t n a t u r e of' parameters of measurement a r e t h e t h e s e d i s l o c a t i o n - r e l a t e d c a r r i e r t r a p s i s same a s f o r Fig. 4. not y e t c l e a r ; t h e proposition t o a s c r i b e

H(.35) t o r e c o n s t r u c t i o n d e f e c t s and E(.4) t o kinks /21/ has not been v e r i f i e d .

%

-

. spectrum of a 850 /420 C deformed specimen.

Fi 6 g i v e s t h e Arrhenius p l o t s of t h e (T9:corrected) e l e c t r o n emission r a t e s , t h e _ " f i n g e r p r i n t s " , f o r t h r e e c l e a r l y d i s t i n -

guishable e l e c t r o n t r a p s . The n o t a t i o n , e.g.

E(.54),only r e f e r s t o t h e slope of t h e s e

4 r 1 0 ~ 5 p , c m ~ Arrhenius p l o t s (0.54eV i n t h i s c a s e ) ; t h e a c t u a l t r a p depth can only be c a l c u l a t e d by t a k i n g i n t o account t h e temperature 8 _. dependence of t h e c a p t u r e c r o s s - s e c t i o n s ,

which a r e not y e t known.

4 , . All t h e s e d e f e c t s show a t y p i c a l , s t r o n g l y non-exponential e l e c t r o n c a p t u r e /22,25/.

Fig. 7 demonstrates t h i s f o r t h e E(.29) t r a p , showing t h e c a p t u r e t o be logarithmic i n f i l l i n g time over 4 o r d e r s of magnitude.

. Moreover, t h i s s t r o n g l y non-exponential c a p t u r e determines t h e f i l l i n g of more than 60% of t h e t o t a l t r a p c o n c e n t r a t i o n , inde- pendent of t h e combination of r e v e r s e b i a s

% v o l t a g e and f i l l i n g pulse height used. This fi2 r e s u l t excludes t h e f r e q u e n t l y observed

I I e f f e c t of t h e f r e e c a r r i e r t a i l i n t h e

100 200 300

Temperature ( K ) d e p l e t i o n region /26/ a s explanation of t h e observed non-exponential c a p t u r e . Rather t h i s

def6500C 07%

a , , , N d ~ n x 1 0 7 c i 2 -

Fig. 4 shows t y p i c a l DLiS s p e c t r a of n-Si samples deformed a t 65% C , Fig. 5 t h e

JOURNAL DE PHYSIQUE

Temperature ( K 1

100

I I I I I I I I I I I I

. 0 0 2 , 0 0 4 . 0 0 6 .OW .010 .012

lOOO/T (K-' )

F i g . 6: E l e c t r o n emission r a t e s o f t b r e e deep l e v e l d e f e c t s i n p l a s t i c a l l y deformed (650 C) n-Si.

3.4. F u r t h e r l e v e l s have been found occasion- F i g . 7 : D L T S l i n e E ( . 2 9 ) , m e a s u r e d n i n d e f o r m e d n - S i . S p e c i f i c a l l y , i t i s w i t h v a r i o u s f i l l i n g p u l s e widths. worth mentioning t h a t t h e E(.68) t r a p c o u l d The i n s e r t demonstrates t h e t y p i c a l n o t be found i n our deformed n-Si samples, l o g a r i t h m i c f i l l i n g over f o u r o r d e r s whdch-5ad a grown-in d i s l o c a t i o n d e n s i t y of o f magnitude f i l l i n g p u l s e d u r a t i o n . 10 cm p r i o r t o deformation. As s t a t e d a l -

ready by Pate1 and K i m e r l i n g /21/, t h i s d e f e c t o f unknown o r i g i n o n l y occurs a f t e r deformation o f an i n i t i a l l y d i s l o c a t i o n f r e e c r y s t a l .

3.2. The prominent peak i n h i g h l y d i s l o c a t e d

Concluding t h i s chapter, i n t h e DLTS spectrum o f deformed s i l i c o n a t l e a s t t h r e e d i f f e r e n t kinds o f t r a p s can be d i s t i n g u i s h e d . Two o f them have been t e n t a t i v e l y a s c r i b e d t o d e f e c t s g i v i n g r i s e t o d i s t i n c t EPR spectra. Whereas t h e q u a l i t a t i v e observations o f f o r m a t i o n and annealing o f EPR spectra and DLTS t r a p s agree, a d i r e c t q u a n t i t a t i v e comparison o f t h e measured t r a p c o n c e n t r a t i o n s i s n o t y e t possible. As t o t h e EPR spectra, Fermi l e v e l e f f e c t s have t o be taken i n t o account.

I I I

n-Si 11-03 4 x d 5 p/crn3 def.l.5% 650°C

EL291 t2= 15 ms

I I I

100 150 2 0 0

G'i@les, E(.54), F i g . 4, i s u n s t a b l e upon annealing a t 800'~. Moreover, i t cannot be found i n low-temperature deformed s i l i c o n , see F i g . 5. Both these observations a r e i n accordance w i t h t h e occurence o f t h e Si-Kl/K2 and "broad l i n e " EPR centers. Moreover, Photo-EPR experiments show c l e a r l y a midgap l e v e l f o r t h e KloK2 t r a n s i t i o n , Fig. 2 /6/.

Thus t h e E(.54) e l e c t r o n t r a p m i g h t be associated w i t h t h e t h e r m a l l y u n s t a b l e d a n g l i n g bond d e f e c t s a t t h e d i s l o c a t i o n core.

3.3. E(.29J and E(.19) t r a p s appear n o t o n l y i n h e 650 C deformed samples, F i g . 4, b u t

as u e l l an t h e low temperature/high s t r e s s 850 /420 specimen, F i g . 5. T h i s p o i n t s towards a c o r r e l a t i o n w i t h t h e i m p u r i t y - r e l a t e d Si-K7 center. Photo-EPR experiments w i t h Si-K7 i n n-Si, compensated by t h e deformation, show indeed t h e e x i s t e n c e o f a Si-K7 l e v e l i n t h e upper h a l f o f t h e band

Ternperoture ( K ) gap.

These m i g h t r e s u l t i n i n s u f f i c i e n t occupation o f t h e defects. For t h e DLTS spectra, Figs. 4,5, g i v e o n l y apparent concentrations, n e g l e c t i n g t h e observed l i n e broadening.

Future experiments w i t h v a r i o u s shallow dopant concentrations should a l l o w t o estab- l i s h even q u a n t i t a t i v e r e l a t i o n s .

4. PHOTO-LUMINESCENCE OF PLASTICALLY DEFORMED SILICON

L a t t i c e d e f e c t s created d u r i n g p l a s t i c deformation of s i l i c o n a r e connected w i t h a remarkably s t r o n g photo-luminescence (PL) e t i s s i o n /30-34, l/. F i g . 8 shows PL spectra o f s i l i c o n samples, deformed a t 650 C i n s t a t i c deformation up t o v a r i o u s d i s l o c a t i o n d e n s i t i e s . A f t e r weak deformation, a s e r i e s o f s t r u c t u r e d l i n e s "Dl-D4"

(Drozdov e t a l . /30/) dominates. Near band-gap emissions 1 i ke e l e c t r o n - h o l e drop1 e t s a r e quenched a t d i s l o c a t i o n d e n s i t i e s i n t h e 107 cm-2 range. Higher d i s l o c a t i o n c o n t e n t leads t o appearance o f a broad emission band between 0.8 and 1.05eV. F i g . 9 shows t h i s broad band t o be t h e r m a l l y u n s t a b l e a t 8500C, connected w i t h t h e appear- ance o f t h e D-1 ines. F i g . 10 d e p i c t s t h e emission o f a 850/4200C h i g h s t r e s s deformed sample: A s t r o n g l i n e a t 0.96eV w i t h unresolved f i n e s t r u c t u r e dominates. Furtheron, a sharp l i n e a t 1.01eV and a weak band near 0.90eV i s present i n such samples. Relax- a t i o n o f t h e f r o z e n - i n s t r a i g h t d i s l o c a t i o n s by heat treatment a t 390% /35/, Fig. 11, y i e l d s again t h e D-series. The 1.OleV l i n e gets dominant i n h i g h - s t r e s s samples, deformed along a [2,1,111-axis, c o n t a i n i n g a h i g h d e n s i t y o f wide s t a c k i n g f a u l t s /36/, Figs. 11, 12.

F i g . 9: PL spectra o f h e a v i l y d i s l o c a t e d

silicon before and a f t e r annealing a t 850OC.

Wavelength X [ ~ m l

Fig. 8: Photo-luminescence emission o f deformed s i l i c o n (650%) w i t h v a r i o u s d i s l o c a t i o n d e n s i t i e s , measured a t 4K u s i n g super-bandgap e x c i t a t i o n .

C4-326

,

3 deformed (0.L %I

- 0

Wavelength A I p m l

-

-

I I

I

:d,L,

Wavelength A ( pml b) S ^{l h at} 390% ^onmoled

:: 14 5 S -

-

?i

15 1 1 13 12 11

These observations suggest t h e f o l l o w i n g d i s t i n c t i o n o f t h e PL emissions:

4.1. The D-series i s connected d i r e c t l y ZTh t h e presence o f d i s l o c a t i o n s . I t has

even been found i n s i l i c o n c o n t a i n i n g d i s - l o c a t i o n s t h a t were introduced by l a s e r annealing. However, t h e D-series cannot be r e l a t e d w i t h t h e p e r f e c t , s t r a i g h t d i s l o c a t i o n as i t i s almost absent i n 8500/420oC h i g h s t r e s s deformed samples.

The remarkable e f f e c t o f s t r e s s r e l a x a t i o n , F i g . 10, r a t h e r suggests t o a s c r i b e t h e 0 - s e r i e s t o k i n k s i n t h e d i s l o c a t i o n s , c f . /38/.

4.2. The broad emission band c o r r e l a t e s i n appearance and annealing w i t h t h e obser- v a t i o n o f dangling-bond EPR centers. As no r e l a t i o n t o d i s l o c a t i o n s can be stated, t h e most probable e x p l a n a t i o n f o r t h i s band a r e p o i n t d e f e c t c l u s t e r s . S i m i l a r l y as f o r t h e broad EPR l i n e , see s e c t i o n 2.1., t h e l i n e w i d t h m i g h t a r i s e from t h e long-ranging s t r a i n f i e l d o f t h e d i s l o c a t i o n s .

4.3. The narrow l i n e a t l.OleV appears and vanishes simultaneously w i t h l a r g e s t a c k i n g

f a u l t s . EBIC i n v e s t i g a t i o n s o f our samples /39/ d i d n o t show any recombination a t s t a c k i n g f a u l t s i n n-Si, so t h a t t h e l e v e l associated w i t h t h i s l i n e m i g h t be a t :

E- - l.OleV e E,, + 0.15eV.

Y

Fig. 10: PL spectra o f 8 5 0 ~ / 4 2 0 ~ ~ high- Remarkably enough, such s t a c k i n g f a u l t s t r e s s deformed s i l i c o n ( a x i s [213]): s t a t e has been p r e d i c t e d by several model a) as-deformed w i t h s t r a i g h t d i s l o - c a l c u l a t i o n s , e.g. /40,41/. The o t h e r new

c a t i o n s l i n e s a t 0.90eV and 0.96eV seem t o c o r r e l a t e b) a f t e r r e l a x a t i o n of t h e d i s l o c a t i o n w i t h t h e occurence o f s t r a i g h t d i s l o c a t i o n s ,

s t r u c t u r e a t 390°C, c f . F i g . 11 a more p r e c i s e model cannot y e t be suggested c ) o n l y 8500C predeformation f o r them.

Si deformed in compression along [2;1,111 (T,=L~O~C,T =350 MPa)

-

a) as deformed b) after annealing (TA = 390°C,12 min.)

Fig. 11: TEM p i c t u r e o f 8 5 0 ~ / 4 2 0 ~ ~ deformed s i l i c o n (H. Gottschalk 1981):

a as-deformed, t h e d i s l o c a t i o n s a r e s t r a i g h t and w i d e l y d i s s o c i a t e d / 3 6 / , b{ a f t e r annealing w i t h o u t s t r e s s , t h e d i s l o c a t i o n s a r e curved and t h e s t a c k i n g

f a u l t s r e l a x e d t o e q u i l i b r i u m w i d t h (<lOnm) /35/.

0.8 0.9 1.0 I.I[eV;

Si: P 4 ^x 10'\m-' 850°/4200C C 2 1 I I 1 deformed 0.2%

1.5 1.4 1.3 1.2 1.1 Wavelength X(ycm)

F i g . 12: PL spectrum o f a 850°/4200c along [ 2 1 111 deformed sample w i t h wide s t a c k i n g f a u l t s , showing t h e 1.OleV emission t o be dominant.

T h i s s h o r t d e s c r i p t i o n shows t h e l i n e s along which f u r t h e r experiments m i g h t proceed.

Information obtained from hydrogenation experiments /33/, t h e use o f u n i a x i a l s t r e s s /34,38/ w i l l soon b r i n g more d e t a i l e d evidence about t h e r a d i a t i v e recombination c e n t e r s i n p l a s t i c a l l y deformed s i l i c o n .

5. CONCLUSIONS

The most i m p o r t a n t r e s u l t s o f EPR, DLTS and PL i n v e s t i g a t i o n s o f deformation induced deep l e v e l defects i n s i l i c o n can be summarized as f o l l o w s :

5.1. The c o r e o f d i s l o c a t i o n s i n s i l i c o n appears t o be g e n e r a l l y reconstructed; t h i s li6T& e s p e c i a l l y f o r t h e s t r a i g h t 30° and 900 p a r t i a l d i s l o c a t i o n s introduced a t low

temperature (4200C), which do n o t produce any EPR s i g n a l .

5.2. D i s l o c a t i o n s i n s i l i c o n g i v e r i s e t o deep l e v e l s a t Ec-0.4eV and Ev+0.35eV.

These d i s l o c a t i o n s t a t e s a r e observed a f t e r a l l kinds o f deformations used up t o now.

5.3. Dangling bond d e f e c t s a r e present o n l y i n c r y s t a l s w i t h curved d i s l o c a t i o n s , W u c e d a t T<-0.6Tm. EPR y i e l d s n a r r o w - l i n e spectra from d e f e c t s r i g h t i n t h e d i s -

l o c a t i o n core (possibly a t j o g s ) , and from p o i n t d e f e c t s o u t s i d e t h e d i s l o c a t i o n s . The a d d i t i o n a l l y observed broad l i n e appears t o be due t o dangling bond defects a t v a r i o u s places near t h e d i s l o c a t i o n s . The E(.54) e l e c t r o n t r a p and a broad PL band a r e formed and anneal s i m i l a r l y as t h e d a n g l i n g bond EPR c e n t e r s ,

5.4. Dopant atoms a t t h e d i s l o c a t i o n core produce f u r t h e r EPR spectra; t h e E(.29) -- t r a p can be c o r r e l a t e d w i t h t h e Si-K7 EPR spectrum ascribed t o a P-related d e f e c t

i n t h e d i s l o c a t i o n core.

5.5. Kinks i n t h e d i s l o c a t i o n s cannot be c o r r e l a t e d w i t h any EPR s i g n a l , however

- t h e y seem t o a c t as r a d i a t i v e recombination centers, g i v i n g r i s e t o t h e "D-series'' PL emission.

5.6. The presence o f wide s t a c k i n g f a u l t s introduced a t 4 2 0 ' ~ i s connected w i t h a a r p I.OleV PL emission, probably a r i s i n g from t r a n s i t i o n s t o a shallow s t a c k i n g

f a u l t s t a t e near EV+O. 15eV.

The e l e c t r i c a l and o p t i c a l p r o p e r t i e s o f d i s l o c a t e d s i l i c o n o b v i o u s l y depend d e c i - s i v e l y on t h e c o n d i t i o n s (temperature, s t r e s s , s t r a i n ) under which the d i s l o c a t i o n s were introduced. Moreover, t h e p o s s i b l e i n f l u e n c e o f r e s i d u a l i m p u r i t i e s , l i k e oxygen, should always be considered, although f o r t h e d e f e c t p r o p e r t i e s discussed here no r e l a t i o n t o background i m p u r i t i e s has been found up t o now. This paper shows, t h a t t h e combination o f EPR i n v e s t i g a t i o n s w i t h v a r i o u s o t h e r experimental methods, a p p l i e d on i d e n t i c a l samples w i t h s p e c i f i c d i s l o c a t i o n s t r u c t u r e s , can y i e l d f i r s t i n f o r m a t i o n on t h e microscopic n a t u r e o f a v a r i e t y o f deformation induced l a t t i c e defects i n s i l i c o n . Nevertheless, t h e p i c t u r e sketched here has t o be t e s t e d and s p e c i f i e d by f u r t h e r experiments i n t h e f u t u r e .

C4-328 JOURNAL DE PHYSIQUE

The a u t h o r s want t o thank t h e i r coworkers H. Gottschalk, K.H. Kiisters and R . Michel f o r v a l u a b l e d i s c u s s i o n s and leaving of unpublished m a t e r i a l . The continuous cooperation with R. Sauer, J . Weber and coworkers concerning PL experiments, with J.R. Patel and L.C. Kimerling, and w i t h H . G . Grinmeiss and P. Omling concerning DLTS measurements i s g r a t e f u l l y acknowledged. The Deutsche Forschungsgemeinschaft gave f i n a n c i a l support.

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