HYDROGENATION EFFECTS ON RADIATIVE RECOMBINATION IN TWISTED SILICON

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HYDROGENATION EFFECTS ON RADIATIVE RECOMBINATION IN TWISTED SILICON

D. Gwinner

To cite this version:

D. Gwinner. HYDROGENATION EFFECTS ON RADIATIVE RECOMBINATION IN TWISTED SILICON. Journal de Physique Colloques, 1983, 44 (C4), pp.C4-141-C4-147.

�10.1051/jphyscol:1983417�. �jpa-00222857�

JOURNAL DE PHYSIQUE

Colloque C4, supplément au n°9, Tome 44, septembre 1983 page C4-141

HYDROGENATION EFFECTS ON RADIATIVE RECOMBINATION IN TWISTED SILICON

D. Gwinner

Institut fiir Angewandte Physik, TV Clausthal, Clausthal-Zellerfeld, F.R.G., und SFB 126, Gottingen-Clausthal, der Deutschen Fovschungsgemeinsohaft

RESUME

Des m o n o c r i s t a u x de s i l i c i u m déformés p a r t o r s i o n , à h a u t e t e m p é r a t u r e ( 1 2 7 0 K , 240°/cm, 90 mn), m o n t r e n t une r é s o n a n c e p a r a m a g n é t i q u e é l e c t r o n i q u e f a i b l e , avec une v a l e u r t y p i q u e de g é g a l e à 2 , 0 0 4 3 . E l l e e s t a t t r i b u é e aux l i a i s o n s p e n d a n t e s i s o l é e s d a n s l e coeur d e s d i s l o c a t i o n s r e c o n s t r u i t e s .

L ' i n t r o d u c t i o n d ' a t o m e s d ' h y d r o g è n e a p r è s d é f o r m a t i o n c o n d u i t en p a r t i e à l ' e x t i n c t i o n du s i g n a l d e p h o t o l u m i n e s c e n c e . Une d e s é m i s s i o n s p r i n c i p a l e s (0,81eV) e t une a u t r e p l u s f a i b l e à 0,84eV r e s t e n t i n c h a n g é e s en i n t e n s i t é , t a n d i s que l a r a i e à 0,87eV e s t a u g m e n t é e . La c o r r é l a t i o n e n t r e l a r a i e à 0 , 8 1 eV e t l e s é t a t s c r é é s p a r l a d i s l o c a t i o n e s t d i s c u t é e .

ABSTRACT

High temperature twisted silicon single crystal (1270K, 240°/cm, 90 min) exhibit a structureless weak electron paramagnetic resonance with a typical g-value of 2.0043. It is attributed to isolated dangling bonds in the cores of reconstructed dislocations.

Incorporation of hydrogen atoms after deformation partly leads to the extin- tion of photoluminescence signals. One of the main emission (0.81eV) and a weaker one at 0.84eV remain unchanged in intensity, while the 0.87eV-line is enhanced.

The correlation of the 0.81eV-signal to dislocation states is discussed.

A high density of split screw dislocations in silicon single crystals can be achieved by torsion around a <lll>-axis at 1270 K and a subsequent 4 hours anneal at 1420K|l|.

under the assumption, that the non-screw dislocations participate in the total dislo- cation structure in the same fractions as in compressed silicon |2|, an increase in the number of 30°-partials by a factor of two compared to the astwisted state can be expected.

Twisted specimens reveal an intense luminescence answer on excitation by light, which is about two orders of magnitude higher than the excitonic luminescence gain |3|.

The radiative transitions can be caused by dislocations, by point defects, and by interaction of both. We investigated the effect of hydrogen incorporation on the photoluminescence spectra, to have a possibility of distinguishing between the diffe- rent defect transitions. Hydrogenation was recently applied to saturate deformation induced defects in compressed specimens, revealed by the DLTS-method |4,5|.

Electron spin resonance measurements were carried out to establish wether the high temperature treatment allows for the existence of deformation produced dangling bonds.

14 -3

Experimental : p- and n-type Si in the doping range of 1-5x10 cm were investigated.

The torsion time at 1270 K was 90 min. The deformation resulted in twist angles of 240°/cm. Some of the twisted samples were annealed at 1420 K for 4 hours. Test samples underwent the same heat treatments.

The photoluminescence spectra were mainly excited by a Nd : Yag-Laser (1064nm, 1 W) and a He-Ne-Laser (633 nm, 25 mW) analysed by a single-grating monochromator (f : 220 mm) and measured with a cooled PbS-detector. The energy resolution was typically 0.015 eV in the region 1.0 eV - 0.75 eV and 0.02 eV below these photon energies.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983417

C4-142 JOURNAL DE PHYSIQUE

The temperature c o u l d be v a r i e d between 10 K and 300

K.

Only f o r t h e s p e c t r a l region 0.4 eV - 0.75 eV t h e s p e c t r a were c o r r e c t e d t o t h e responce of t h e d e t e c t i o n system. F.t h i g h e r photon e n e r g i e s no important change was caused by t h e system f u n c t i o n .

Measurements a t 4.2 K , w i t h h i g h e r s e n s i t i v i t y and higher r e s o l u t i o n (0.01 eV) were made p o s s i b l e by t h e f a c i l i t i e s of P h y s i c a l I n s t i t u t e , Dept. 4 , U n i v e r s i t y of S t u t t g a r t : Ar-Ion-Laser (300 mW)

,

s i n g l e - g r a t i n g monochromator

(f

: 7 5 0 mm)

,

c o o l e d Ge-P/N-detector.

For hydrogenation, a plasma beam c o n t a i n i n g a t l e a s t 50 % atomic hydrogen impinged on t h a t f a c e of t h e c r y s t a l , from which t h e luminescence should be e x c i t e d . The plasma beam, g e n e r a t e d i n s i d e a g l a s t u b e where a c o n s t a n t H2-gas p r e s s u r e o f 6 m b a r was maintained, caused t h e specimen t o h e a t up. The temperature was c o n t r o l l e d by t h e power of t h e 27 MHz-Generator. Within t h e l o a d i n g time of 90 min, t h e tempera- t u r e was r e g u l a t e d from 640 K t o 570 K i n 30 min-steps.

Before plasma t r e a t m e n t , t h e specimens were e t c h e d i n 1 HF

+

7 HNOj f o r 20 s e c . Some of them were e t c h e d a f t e r hydrogenation f o r 5 s e c .

The EPR-spectra were recorded with a 9.24 GHz-Spectrometer i n t h e a d i a b a t i c f a s t passage mode below 30 K. During sweep of magnetic f i e l d , t h e samples could be i l l u - minated by a 100 W-tungsten-lamp through a s i n g l e - p r i s m monochromator.

0. 75 0. 85 0.95

PHOTON ENERGY (EV)

Fig. 1: Twisted s i l i c o n (A) a f t e r a 4 hours anneal a t 1420 K ( 6 ) . Ge-Detector.

From f i g . 1 it can be seen t h a t t w i s t i n g g e n e r a t e s t h e same photoluminescence s i g - n a l s a s t h e y a r e p r e s e n t i n t h e s p e c t r a of compressed S i 161 ^: Dl (0.81 eV)

,

D2

(0.87 eV), D3 (0.93 eV), D4 (0.99 eV)

.

T y p i c a l l y t h e main i n t e n s i t y Dl i s h i g h e r by a f a c t o r of about 20 than D3 and D4. D2 amounts only t o 20 B of t h e h e i g h t of Dl, whereas a f t e r compression i t

i s

of t h e same o r d e r of magnitude a s Dl.

A d d i t i o n a l l y , two i n t e n s e l i n e s a p p e a r i n t h e n e i g h b o u r h o o d o f Dl: 2 ( 0 . 7 9 eV) a n d 3 ( 0 . 7 8 eV)

,

a s w e l l a s a b r o a d h i l l a r o u n d 0 . 8 4 e V ( 1 ) .

T h e 0 . 7 8 c V - l i n e c a n b e g e n e r a t e d I n c o m p r e s s e d s p e c i m e n s (1060 K , l o 8 d i s l o c a - t i o n s ) by a 9 0 min a n n e a l a t 1 2 7 0 K .

A f t e r a n n e a l i n g a t 1420 K , t h e s p e c t r a l s h a p e i s m a i n t a i n e d . T h e t o t a l i n t e n s i t y d e c r e a s e s t o 3 0 % . T h e maximum d e c r e a s e t h r o u g h o u t a l l m e a s u r e m e n t s was by o n e o r - d e r o f m a g n i t u d e . R e l a t i v e t o t h e o t h e r s i g n a l s , Dl i n c r e a s e d s l i g h t l y .

0. 40 0.50 0.60 0.70 0. 70 0.80 0.90

PHOTON ENERGY CEV) PHOTON ENERGY (EV)

F i g . 2 b F i g . 2 a

F i g . 2: T w i s t e d s i l l c o n (A) a f t e r a 4 h o u r s a n n e a l a t 1 4 2 0 K (B). P b S - D e t e c t o r . S p e c t r a r e c o r d e d i n t h e l o w e r r e s o l u t i o n a p p a r a t u s a n d e x c i t e d by t h e l i g h t o f a Nd:Yag-Laser a r e shown i n f i g . 2 . D4 c o u l d n o t b e d i s t i n g u i s h e d f r o m t h e z e r o l i n e a n d D3 i s n o t r e s o l v e d . T h e r e

i s

a r e l a t i v e i n t e n s i t y c h a n g e b e t w e e n Dl a n d 3 . T h e r e a s o n f o r t h e a b s e n c e o f D2 i s n o t o n l y t h e l o w e r r e s o l u t i o n , b u t a l s o t h e c h a n g e i n w a v e l e n g t h o f e x c i t i n g l i g h t . F o r t h e same e x c i t a t i o n d e n s i t y t h e s i g n a l i s l o w e r e d a t l e a s t by 5 0 % when i n f r a r e d i n s t e a d o f v i s i b l e l i g h t i s s h i n e d o n t h e s a m p l e . T h i s d e p e n d e n c e o n p e n e t r a t i o n d e p t h was c ~ n f i r m c d i n t h e h i g h e r r e s o l u t i o n a p p a r a t u s f o r c o m p r e s s e d s a m p l e s i l l u m i n a t e d w i t h a Nd:Yag-Laser.

Two a d d i t i o n a l l u m i n e s c e n c e s i g n a l s w e r e f o u n d i n t h e low e n e r g y r e g i m e ( f i g . 2 b ) : 4 ( 0 . 7 4 e V ) , 5 (0.5 e V ) , w h i c h c a n n o t b e a n n e a l e d o u t . Compared t o t h e f i r s t p a r t o f t h e s p e c t r u m t h e i r i n t e n s i t y a m o u n t s o n l y t o 5 % of. t h e h i g h e n e r g y e m i s s i o n s . T h e b r o a d band. a r o u n d 0.5 eV i s a l s o m e a s u r e d i n low t e m p e r a t u r e c o m p r e s s e d s a m p l e s

( 9 5 0 K) w i t h h i g h d i s l o c a t i o n d e n s i t i e s (>

lo9

The i n f l u e n c e o f h y d r o g e n on Che s p e c t r a i s i l l u s t r a t e d i n f i g s . 3 , 4 .

The n e i g h b o u r s t o Dl a r e d r a s t i c a l l y r e d u c e d , s o t h a t Dl i s t h e p r e d o m i n a n t s i g n a l . D2 w h i c h i s n o t m e a s u r e d i n t h e a s - d e f o r m e d s t a t e i n c r e a s e s , a n d i s c l e a r l y s e p a - r a t e d from h i l l 1 i f t h e s a m p l e i s e t c h e d a f t e r h y d r o g e n a t i o n ( f i g . / l a ) .

JOURNAL

DE

PHYSIQUE

0. 40 0.50 0. 60 0. 70

PHOTON ENERGY (EV)

1 1 1 ' 1 ~ 1 1 1 '

T-1OK

HE-NE-LASER, A. 0- NO-YAG-LASER, C

0.75 0.85 0.95

PHOTON ENERGY (EV)

F i g . 3 b F i g . 3 a

F i g . 3: T w i s t e d u n a n n e a l e d s i l i c o n ( A ) a f t e r h y d r o g e n a t i o n (B,C)

.

PbS-Detector

.

I n t h e second p a r t of t h e s p e c t r a ( f i g s . 3b, 4b) s i g n a l 5 v a n i s h e d and 4 c a n n o t b e d i s t i n g u i s h e d from t h e t a i l of D l . While t h e t o t a l i n t e n s i t y d r o p s t o 1 0 %, t h e maximum i n t e n s i t y i s n e a r l y unchanged a b o v e 0.75 eV. I f t h e h y d r o g e n a t e d s u r f a c e

i s

e x c i t e d by a Nd:Yag-Laser, t h e n t h e i n i t i a l s t a t e is n e a r l y r e s t o r e d , a s d e p i c t e d i n f i g s . 3.3, 3b.

The p r o p e r t i e s o f D3, D 4 c o u l d n o t b e s t u d i e d b e c a u s e of t h e i r t o o low i n t e n s i t y . T w i s t e d b u t u n a n n e a l e d samples g i v e r i s e t o a weak EPR-signal, which c a n be d o u b l e d i n a m p l i t u d e by i l l u m i n a t i n g w i t h 2 1.0 eV-photons.

An example i s g i v e n i n f i g . 5, where t h e a b s o r p t i o n m a x i ~ m c o r r e s p o n d s t o g = 2.0043, y i e l d i n g a t o t a l number of s p i n s of a b o u t 10

.

The g - v a l u e s f o r o t h e r samples are r a n g i n g from 2.0040 t o 2.0050. I n t e s t specimens no EPR c o u l d b e d e t e c t e d .

8. 48 8. 50 0.68 8.78 PHOTON ENERCY (EV)

I . , . I . I . I *

T-lOK

HE-NE-LASER -

8. 75 0. 85 0. 95

PHOTON ENERCY (EV)

Fig. 4 b Fig. 4 a

Fig. 4: Twisted unannealed silicon (A) after hydrogenation and etching ( B )

.

PbS-Detector

.

Fig. 5: EPR-signal of twisted silicon (1270 K, 9 0 rnin). Adiabatic fast passage.

Sample illuminated.

JOURNAL DE PHYSIQUE

D i s c u s s i o n :

The h i g h e s t d e f o r m a t i o n t e m p e r a t u r e which a l l o w s t o measure p a r a m a g n e t i c r e s o n a n c e s i n s i l i c o n

i s

r e o r t e d t o b e 1165 K 17,81. Compressed specimens w i t h d i s l o c a t i o n d e n s i t i e s

<

6-10tj cm-2 r e v e a l a s t r u c t u r e l e s s EPR-signal whose g - v a l u e v a r i e s b e t - ween 2.0034 and 2.0052. I t c o u l d b e r e d u c e d below t h e l i m i t of d e t e c t i o n by two h c u r s annealing a t 1120 K.

I t i s o b v i o ~ s l y t h i s r e s o n a n c e we found i n h i g h t e m p e r a t u r e (1270 K) t w i s t e d s a m p l e s , b e c a u s e t h e g - v a l u e s a r e n e a r l y i d e n t i c a l .

A t h i g h d e f o r m a t i o n t e m p e r a t u r e s , e n e r g y

i s

p r o v i d e d t o s u p p o r t t h e 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 c o r e s ( 9 , l O

1.

S o t h e EPR-signal c a n n o t be c a u s e d by l i n e a r c h a i n s of d i s l o c a t i o n d a n g l i n g bonds ( d b ' s ) . The p o s s i b l e o r i g i n s a r e s h o r t u n r e - c o n s t r u c t e d l e n g t h s a n d s i n g l e d b ' s s e p a r a t i n g a d j e s c e n t r e c o n s t r u c Q d p a r t s ( a n t i - p h a s e p o i n t s ) . These p o i n t s a r e c o r r e l a t e d t o " d i s l o c a t i o n d e f e c t s " , l i k e p o i n t d e f e c t s i n t e r a c t i n g w i t h t h e c o r e , k i n k s , j o g s and n o d e s . O n i t t i n g t h e i n f l u e n c e o f p o i n t d e f e c t s , t h e d e n s i t y o f d i s l o c a t i o n d e f e c t s i s i n c r e a s e d w i t h i n c r e a s i n g d i s l o c a t i o n d e n s i t y . I n t w i s t e d samples it i s one o r d e r o f magnitude h i g h e r t h a n i n t h e specimens of r e f . 7. E s p e c i a l l y t h e d e n s i t y o f nodes i s h i g h b e c a u s e of t h e p r e s e n c e of n e t w o r k s even i n t h e u n a n n e a l e d samples 11

1 .

The h i g h d i s l o c a t i o n d e n s i t y of low t e m p e r a t u r e compresserlsamples i n presumably t h e r e a s o n f o r a r e s i d u a l EPR-signal a f t e r a n n e a l i n g o f t h e i n t e n s e d e f o r m a t i o n induced l i n e s

I

11

I .

B e s i d e s a t d i s l o c a t i o n d e f e c t s , hydrogen atoms c a n be i n c o r p o r a t e d i n t w i s t e d s i l i - con a t p o i n t d e f e c t s o r a t d i s l o c a t i o n s , i f t h e r e c o n s t r u c t i o n i s l o c a l l y d e s t r o y e d by t h e hydrogen i t s e l f .

Within t h e p e n e t r a t i o n d e p t h of t h e Ne-Ne-Laser l i g h t (r: 10 p n ) h y d r o g e n a t i o n a l t e r s t h e d e f e c t s t r u c t u r e a n d g i v e s r i s e t o changes i n t h e l u m i n e s c e n c e s p e c t r a . While s i g n a l s 5 ( 0 . 5 eV)

,

4 (0.74 eV)

,

3 (0.78 eV)

,

2 ( 0 . 7 9 eV) d i s a p p e a r e d , ~ 2

( 0 -87 eV) i n c r e a s e d .

E x c i t i n g a c r y s t a l volume d e e p below t h e plasma t r e a t e d s u r f a c e (> 1 0 0

urn)

^{shows no}

e f f e c t of h y d r o g e n a t i o n on t h e s p e c t r a . So t h e hydrogenated l a y e r e x t e n d s a t l e a s t tc 10 l.lm i n s i d e t h e s a m p l e .

The i n t e n s i t y o f D2 depends on t h e s u r f a c e c o n d i t i o n a f t e r h y d r o g e n a t i o n . T h i s i s a f u r t h e r h i n t t o a d i s l o c a t i o n - s u r f a c e i n t e r a c t i o n as a n o r i g i n o f t h i s lumines- c e n c e l i n e . E t c h i n g o f a non-hydrogenated sample d o e s n o t a f f e c t i t s i n t e n s i t y . The 0.78 eV-emission i s c a u s e d by a h i g h t e m p e r a t u r e g e n e r a t e d d e f e c t which n e e d s d i s l o c a t i o n s f o r

i t s

s t a b i l i z a t i o n . Complexes o f p o i n t d e f e c t s n e a r t h e d i s l o c a - t i o n s c a n b e t h e c h a r a c t e r i z a t i o n o f t h i s d e f e c t t y p e , which may c o n t a i n broken c o v a l e n t bonds.

The r e c o m b i n a t i o n l i n e s D l (0.81 eV) and 1 (0.84 eV) a r e e v i d e n t l y n o t i n f l u e n c e d . T h i s o b s e r v a t i o n c a n b e d i s c u s s e d a s f o l l o c . ~ ~ :

I n t w i s t e d samples competing n o n r a d i a t i v e c e n t e r s a r e n e g l i g i b l e , s o t h a t D l and 1 a r e t h e main r a d i a t i v e t r a n s i t i o n s . Though some of t h e Dl - and 1 - r e l a t e d de- f e c t s

are

s a t u r a t e d , t h e r a d i a t i v e g a i n

i s

n o t changed. But t h e n must b e e x p l a i n e d , why s i g n a l 2 c a n be d r a s t i c a l l y reduced from a n e f f i c i e n t t r a n s i t i o n , comparable

t o

s i g n a l D l , t o a l m o s t z e r o q a i n . T h i s i s p o s s i b l e , i f D l c o r r e l a t e s t o a n e a r l y c o m p l e t e l y r e c o n s t r u c t e d d i s l o c a t i o n , which d o e s h a r d l y i n t e r a c t w i t h hydrogen atoms.

The s i g n a l 2

-

r e l a t e d d e f e c t s h o u l d t h e n p o s s e s s a h i g h d a n g l i n g bond d e n s i t y . An i d e n t i f i c a t i o n o f t h e D l - c e n t e r w i t h r e c o n s t r u c t e d 3 0 ° - p a r t i a l d i s l o c a t i o n s

i s

n o t ' e v i d e n t from t h e s p e c t r a of a n n e a l e d samples ( f i g . 1 ) . T h e r e i s no c l e a r c o r r e - l a t i o n between t h e i n c r e a s e i n f r a c t i o n o f 3 0 ° - p a r t i a l s and t h e i n t e n s i t y . I f t h e D l - c e n t e r i s a h i g h l y e f f i c i e n t r e c o m b i n a t i o n c e n t e r , t h e n i t s predominance i n a s - t w i s t e d specimens c a n b e e x p l a i n e d . T h i s i s s u p p o r t e d hy t h e f a c t t h a t i n d e p e n d e n t of d e f o r m a t i o n p r o c e d u r e and d e f o r m a t i o n t e m p e r a t u r e , Dl is always one of t h e p r o - minent luminescence l i n e s i n s i l i c o n .

I f t h e D l - c e n t e r ( 0 . 8 1 e V ) c o r r e s p o n d s t o t h e DLTS e l e c t r o n t r a p E c - 0 . 3 8 e V , w h i c h s u r v i v e s temperature t r e a t m e n t s up t o 1 1 7 0 K

1121,

t h e n i t s hydrqqenation

behaviour

should be s t u d i e d a f t e r l o w temperature c a n p r e s s i o n a s i t w a s applied f o r DLTS- m e a s u r e m e n t s ) 4 , 5 )

.

F i r s t r e s u l t s s h o w t h a t it i s n o t reduced a f t e r p l a s m a

t r e a t -

m e n t . S i g n a l 5 ( 0 . 5 e V ) i s t h e o n l y v a n i s h i n g e m i s s i o n and perhaps a t t r i b u t e d t o i s o l a t e d d a n g l i n g b o n d s . T h e i n v e s t i g a t i o n

i s c o n t i n u e d

(V.V. K v e d e r , D. G w i n n e r ;

t o

be p u b l i s h e d )

.

T h e a u t h o r w o u l d l i k e

t o

t h a n k P r o f . R . L a b u s c h a n d D r . V. K v e d e r f o r h e l p f u l d i s c u s s i o n s a n d H. D i e t r i c h for m e a s u r i n g t h e E P R - s p e c t r a .

R e f e r e n c e s :

1

¹¹ GWINNER, D. and P A C K E I S E R , G . , P h i l . M a g .

A42

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K I R S C H T , F.G. a n d DOERSCHEL, J . , p h y s . s t a t . s o l . ( a )

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F i z . 82

( 1 9 8 2 ) , 2068

1

⁶¹ D R O Z W V , N . A . , P A T R I N , A.A. and TKACHEV. V . D . , S o v . P h y s .

-

J E T P L e t t .

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( 1 9 7 6 1 , 5 9 7

]

71 ALEXANDER, H . , LABUSCH, R. and SANDER, W., S o l i d S t . CoIninun.

1

( 1 9 6 5 ) , 357

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W ~ H L E R , F . D . and ALEXANDER, H . , J . P h y s . C h e m . S o l i d s

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^{91 MARKUIND,}

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P A T E L , J .R. and KIMERLING, L . C . , C r y s t . R e s e a r c h a n d T e c h n o l .

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