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DISLOCATION DEFECT STATES IN SILICON
J. Patel, L. Kimerling
To cite this version:
J. Patel, L. Kimerling. DISLOCATION DEFECT STATES IN SILICON. Journal de Physique Col-
loques, 1979, 40 (C6), pp.C6-67-C6-70. �10.1051/jphyscol:1979614�. �jpa-00219030�
JOURNAL DE
PHYSIQUE CoZZoque
C6,suppZ6ment au n06, tome 40, j u i n 1979, page C6-67
DISLOCATION DEFECT STATES IN SILICON
J.R. Pate1 and L.C. K i m e r l i n g
Be22 L a b o r a t o r i e s , Murray H i Z Z , New J e r s e y ,
U. S . A.Resume.- Une methode de s p e c t r o s c o p i e p a r c a p a c i t e t r a n s i t o i r e a e t @ u t i l i s e e p o u r l ' e t u d e des n i - veaux d ' e n e r g i e i n t r o d u i t s dans l e s i l i c i u m p a r d e f o r m a t i o n p l a s t i q u e a 770°C. Une grande v a r i e t e de n i v e a u x a e t e observee avec un n i v e a u p r e p o n d e r a n t a E ( E -0.68eV) aprPs d e f o r m a t i o n . L a v a r i a t i o n de l a c o n f i g u r a t i o n des d i s l o c a t i o n s p a r une d o u b l e d6formaEion ne change pas l e s s p e c t r e s de capa- c i t e observes apres une simple d e f o r m a t i o n . AprGs r e c u i t a 900°C l e s s p e c t r e s se s i m p l i f i e n t e t mon- t r e n t seulement deux n i v e a u x d ' e n e r g i e dominant a E(Ec-0.38eV) e t H(Ev+0.35eV).
A b s t r a c t . - Capacitance t r a n s i e n t spectroscopy has been used t o s t u d y t h e d e f e c t s t a t e s i n t r o d u c e d i n t o s i l i c o n by p l a s t i c d e f o r m a t i o n a t 770°C . A l a r g e v a r i e t y o f d e f e c t s t a t e s a r e observed w i t h a prominent s t a t e a t E(E -0.68eV) a f t e r d e f o r m a t i o n . V a r y i n g t h e d i s l o c a t i o n s t r u c t u r e by a two s t a g e d e f o r m a t i o n procedure $ i d n o t change t h e observed c a p a c i t a n c e s p e c t r a a f t e r d e f o r m a t i o n . Upon annea- l i n g a t 900°C t h e s p e c t r a s i m p l i f y t o two dominant s t a t e s a t E(Ec-0.38eV) and H(Ev+0.35eV).
E l e c t r i c a l measurements on deformed semiconduc- t o r s u s i n g a v a r i e t y o f t e c h n i q u e s have y i e l d e d d i s - l o c a t i o n d e f e c t s t a t e energy p o s i t i o n s t h r o u g h o u t t h e energy gap /1-4/. Haasen /5/, S c h r o t e r /5,6/, Labusch /6/ and a s s o c i a t e s , u s i n g a m o d i f i e d Read approach /I/, have proposed t h a t t h e c u r r e n t e x p e r i - mental f i n d i n g s m a i n l y i n p - t y p e s i l i c o n , a r e i n accord w i t h t h e e x i s t e n c e o f a band o f s t a t e s a t Ev + 0.34 eV f o r 60" d i s l o c a t i o n s . I n c o n t r a s t , Graz- h u l i s e t a l . /7/, i n t e r p r e t i n g H a l l e f f e c t d a t a d i - r e c t l y i n n and p t y p e s i l i c o n , f i n d l e v e l s a t Ev +
0.42 eV and Ec - 0.43 eV. A dominant r e c o m b i n a t i o r c e n t r e i s observed d i r e c t l y a f t e r d e f o r m a t i o n b y L e p i n e e t a l . /8/ a t Ec - 0.67 eV f r o m s p i n depen- d e n t p h o t o c o n d u c t i v i t y s t u d i e s . F i n a l l y , t h e e f f e c t s o f doping on d i s l o c a t i o n v e l o c i t y have been i n t e r - p r e t e d i n terms o f a l e v e l Ev + 0.6 E (correspon-
9
d i n g t o Ec - 0.4 eV a t t h e measurement temperatures) by Pate1 e t a l . / 9 / .
Recently, c a p a c i t a n c e t r a n s i e n t measurements have been a p p l i e d t o h i g h p u r i t y deformed s i l i c o n
/ l o / N-type samples
( p> 10a cm) c o n v e r t e d t o p - t y p e f o l l o w i n g d e f o r m a t i o n , w h i l e m a t e r i a l i n i t i a l l y p- t y p e remained h i g h r e s i s t i v i t y p - t y p e . The dominant r e c o m b i n a t i o n c e n t r e produced i n b o t h m a t e r i a l s was observed as an e l e c t r o n e m i s s i o n s t a t e E(0.68 eV).
1. Experimental .- F l o a t i n g zone c r y s t a l s o f s i l i c o n ( d i s l o c a t i o n - f r e e ) were deformed i n a s i l i c o n com- p r e s s i o n chamber a t t e m p e r a t u r e s o f 750 - 770°C. F o r c a p a c i t a n c e s t u d i e s samples were c u t p a r a l l e l t o t h e p r i m a r y s l i p p l a n e . The specimens were Syton p o l i s h e d and cleaned, and S c h o t t k y b a r r i e r j u n c t i o n s were evaporated on t h e p o l i s h e d s u r f a c e a t room tempera-
t u r e .
Capacitance t r a n s i e n t spectroscopy methods have been reviewed by M i l l e r e t a1 . /11/. The measu- rement d e t e r m i n e s t h e a c t i v a t i o n energy f o r e x c i t a - t i o n o f a c a r r i e r bound a t a d e f e c t s t a t e t o t h e r e l e v a n t band. T h i s a c t i v a t i o n energy i s e s s e n t i a l l y independent o f t h e band bending, Fermi l e v e l v a r i a - t i o n s , o r o c c u p a t i o n f a c t o r s which a r e parameters i n c o r e s t r u c t u r e models and some d a t a a n a l y s i s sche- mes. The d e f e c t s t a t e s p e c t r a e x h i b i t a peak a t a t e m p e r a t u r e where t h e thermal e x c i t a t i o n r a t e f o r a d e f e c t i s equal t o an i n s t r u m e n t a l r a t e window,
T ~ - ' .The a c t i v a t i o n e n e r g i e s a r e denoted E() f o r e l e c t r o n e m i s s i o n t o t h e c o n d u c t i o n band and H ( ) f o r h o l e e m i s s i o n t o t h e v a l e n c e band.
2. R e s u l t s . - 2 .l. N I t y p g - S j l j c o n - l n - , ~ I , ~ ~ c m ~ ~ ) . -
The d e f e c t s t a t e spectrum r e p r e s e n t a t i v e o f samples doped a t 3 ~ 1 0 ~ ~ c m - ~ w i t h phosphorous and deformed a t 770°C i s shown i n f i g u r e 1. A t t h i s r e l a t i v e l y h i g h doping t h e specimen remained n - t y p e a f t e r deforma- t i o n . A l o n g d u r a t i o n ( 1 ms) f i l l i n g t i m e was employ- ed t o observe a l l d e f e c t s t a t e s which a c t as m a j o r i - ty c a r r i e r t r a p s ( e l e c t r o n s ) . A complex spectrum o f o v e r l a p p i n g s i g n a l s i s observed. The most p r o m i n e n t peaks have been i d e n t i f i e d by t h e i r v a r i o u s E va- l u e s . The d e f d c t s t a t e d e n s i t y cannot be p r e c i s e l y r e l a t e d t o t h e ~ a v e r a g e d i s l o c a t i o n d e n s i t y because o f i n h o m o g e n e i t i e s observed i n t h e d e f o r m a t i o n p r o - cess ( s l i p bands).
The peak w i t h t h e l a r g e s t c a p t u r e c r o s s sec- t i o n E(0.68) observed i n l i g h t l y doped n - t y p e c r y s - t a l s / l o / has a p p a r e n t l y s h i f t e d s l i g h t l y t o E(0.63) w i t h t h e doping i n c r e a s e o f 2 o r d e r s o f magnitude
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979614
C6-68 JOURNAL
DE PHYSIQUE
t o 4 x l 0 ' ~ c m - ~ . T h i s s t a t e was observed b y L e p i n e e t a l . / 8 / and i n t h e l i f e t i m e measurements o f Glaenzer and Jordan /11/.
F i g . 1 : D e f e c t s t a t e spectrum c h a r a c t e r i s t i c o f n - t y p e s i l i c o n ,
p< 10R - cm, deformed a t 770°C. The measured d e f e c t s t a t e d e n s i t y averages a s p a t i a l l y n o n - u n i f o r m d i s l o c a t i o n d e n s i t y (=108cm2).
O t h e r peaks observed a r e E(0.48), E(0.41), E(0.28), E(0.18). C o n f i r m a t i o n t h a t peak E(0.63) has t h e l a r - g e s t c a p t u r e c r o s s s e c t i o n i s o b t a i n e d f r o m measu- rement o f t h e d e f e c t s t a t e f i l l i n g t i m e s . F i g u r e 2 shows a s e r i e s o f s p e c t r a o b t a i n e d w i t h f i l l i n g ti- mes v a r y i n g f r o m 100 ns t o 100 u s .
I ti s e v i d e n t t h a t t h e a m p l i t u d e s o f a l l o f t h e peaks v a r y . Howe- v e r , t h e peak E(0.63) m a i n t a i n s i t s maximum a m p l i t u - de even f o r t h e s h o r t e s t f i l l i n g t i m e , i n d i c a t i n g t h a t i t s c a p t u r e c r o s s s e c t i o n i s h i g h ( a n > 3 x 10-16cm2) .
TEMPERATURE
( K )F i g . 2 : Capture c r o s s s e c t i o n d e t e r m i n a t i o n f o r E(0.63). The f i l l i n g t i m e s f o r each spectrum i n d i c a - t e t h e l e n g t h o f t i m e t h a t t h e d e f e c t s t a t e i s ex- posed t o f r e e m a j o r i t y c a r r i e r s .
The d e f e c t s t a t e spectrum shown i n f i g u r e 1 i s c h a r a c t e r i s t i c o f al.1 specimens i n t h a t d o p i n g range and d e f o r m a t i o n temperature. F i g u r e s 3a and 3b e x h i b i t d i s l o c a t i o n morphologies observed i n t h e TEPl a f t e r two d i f f e r e n t d e f o r m a t i o n schedules.
F i g u r e 3a d e p i c t s t h e t a n g l e d d i s l o c a t i o n network c h a r a c t e r i s t i c o f a 5% deformation a t 770°C. F i g u r e 3b shows t h e d i s l o c a t i o n arrangement produced by d e f o r m a t i o n a t 770°C f o l l o w e d by a second deforma- t i o n under h i g h s t r e s s a t 450°C. The morphology i s s i m i l a r t o t h a t observed b y Wessel and Alexander /13/ f o r a s i m i l a r d e f o r m a t i o n . However, v e r y s i m i - l a r d e f e c t s t a t e s p e c t r a were o b t a i n e d i n t h e two cases ( F i g . 1 ) . T h i s r e s u l t suggests t h a t t h e e l e c - t r i c a l p r o p e r t i e s o f deformed s i l i c o n a r e n o t u n i - q u e l y determined by t h e s t r u c t u r e o f t h e induced d i s l o c a t i o n s .
F i g . 3 : TEM micrographs o f as-deformed s i l i c o n . ( a ) € = 5%, T ( d e f . ) = 770°C. ( b )
E =2.2%, T ( d e f . )
= 750°C +
T= 11 kg/mm2, 450 "C. ( P . Mochel and D.M. Maher, u n p u b l i s h e d ) .
2.2. A n n e a l i n g i n t h e Range 700-1000°C.- I t i s w e l l
known t h a t complex p o i n t d e f e c t s a r e i n t r o d u c e d a f -
t e r d e f o r m a t i o n . These d e f e c t s u s u a l l y anneal a t
r e l a t i v e l y moderate temperatures w h i l e r e l a t i v e l y
h i g h temperatures ( n e a r t h e m e l t i n g p o i n t ) a r e r e -
q u i r e d t o d r a s t i c a l l y change t h e d i s l o c a t i o n s t r u c -
t u r e . To t e s t t h i s we have c a r r i e d o u t s u c c e s s i v e
i s o c h r o n a l anneals on t h e deformed specimen, w i t h
s p e c t r a as shown i n f i g u r e 1. The s p e c t r a f o l l o w i n g
J.R. Pate1 and L.C. Kimerling C6-69
annealing f o r one hour a t 700, 800, and 900°C a r e shown i n f i g u r e 4.
F i g . 5
:TEM micrograph o f deformed s i l i c o n sample
(E= 5%, T(def) - 770°C) a f t e r 1 h. (He), 900°C an- neal. ( P . Mochel and D.M. Maher, unpublished).
I n p-type s i l i c o n a broad spectrum centered about H(0.35) i s observed f o l l o w i n g 900°C anneal.
The estimated band w i d t h i s 0.15 eV and hole capture cross s e c t i o n i s
0> 5 ~ 1 0 ~ ~ c m ~ .
TEMPERATURE ( K )
F i g . 4 : I n f l u e n c e o f annealing on d e f e c t s t a t e spec- t r a o f low r e s i s t i v i t y , n-type, deformed s i 1 icon.
The f e a t u r e l e s s l i n e s i n d i c a t e t h e diode capacitance ( r i g h t v e r t i c a l a x i s ) .
The f e a t u r e l e s s curve i n d i c a t e s t h e diode capaci tan- ce ( r i g h t - h a n d s c a l e ) , r e f l e c t i n g t h e f r e e c a r r i e r concentration. A t 700°C a l l o f t h e peaks observed i n f i g u r e 1 are present w i t h s l i g h t changes i n r e l a t i v e amplitude and d e f e c t c o n c e n t r a t i o n compared t o the spectrum a f t e r deformation. The values o f the diode capacitance versus temperature i n d i c a t e s t h a t t h e specimen i s somewhat compensated by acceptors i n - troduced d u r i n g deformation. At 800°C the spectrum s i m p l i f i e s . Some peaks have disappeared and t h e ca- pacitance curve i s f l a t over t h e temperature range i n d i c a t i n g n e g l i g i b l e compensation by shallow d e f e c t s t a t e s (capacitance v o l t a g e measurements y i e l d a f r e e c a r r i e r c o n c e n t r a t i o n o f 2 ~ 1 0 ' ~ c m - ~ , n-type a t room temperature). A t 900°C the annealing process has reached a s t a b l e c o n f i g u r a t i o n i n t h a t f u r t h e r annealing a t 1000°C has l i t t l e i n f l u e n c e on t h e spec- trum shown. We are l e f t w i t h one major peak E(0.38) and the capacitance has f u l l y recovered t o i t s pre- deformation value.
F i g u r e 5 shows a TEM micrograph a f t e r t h e 900°C annealing treatment. Both t h e one and two stage de- formations show t h e same s t r u c t u r e . The d i s l o c a t i o n d e n s i t y i s decreased and t h e most prominent f e a t u r e s a r e loops and h i g h l y r e g u l a r d i p o l e s . The r e s u l t i n g t r a n s i e n t capacitance spectra, a r e l i k e w i s e , t h e same f o r both types o f deformation p l u s anneal.
2.3. Djzcul$j".- These s t u d i e s have several f e a t u - r e s i n common w i t h previous i n v e s t i g a t i o n s o f t h e e l e c t r i c a l behaviour o f d i s l o c a t i o n s by i n v e s t i g a -
t o r s u s i n g o t h e r techniques.
(1) The i n t r o d u c t i o n of acceptors i n n-type s i l i c o n f o l l o w s c l o s e l y t h e i n t r o d u c t i o n o f s p i n centers /8, 14, 15, 16/. S p e c i f i c a l l y Wohler e t a l . /14/
(who s t a t i c a l l y deformed i n compression a t 770°C) have f o l l o w e d t h e i n t r o d u c t i o n and anneal o f s p i n centres. The anneal o f t h e s p i n centres and t h e d e f e c t s t a t e a t E(0.68) occurs i n t h e same temperature range (700-900°C). A s i g n i f i c a n t f r a c t i o n o f these centres have been r e l a t e d t o p o i n t d e f e c t c l u s t e r s produced by deformation /16/. I n germanium Tweet /17/ i n a very e a r l y paper p o i n t e d o u t t h a t h i g h temperature anneals up t o 800°C, 1/2 h were necessary t o anneal o u t defects produced d u r i n g p l a s t i c deformation.
(2) A s t a t e a t Ec - 0.67 eV has been detected by s p i n dependent p h o t o c o n d u c t i v i t y experiments d i - r e c t l y a f t e r deformation (no annealing e f f e c t s were i n v e s t i g a t e d i n these measurements). A s t a t e i n t h e v i c i n i t y o f Ec - 0.6 eV has been r e p o r t e d t o dominant b u l k 1 if e t i m e /12/ and device gene- ration-recombination /18/ p r o p e r t i e s a f t e r d e f o r - mation.
(3) For p-type s i l i c o n a band o f s t a t e s near Ev +
0.34 eV f o r 60' d i s l o c a t i o n s has been r e p o r t e d
by t h e Gottingen group /6/ from H a l l E f f e c t s t u -
d i e s . This r e s u l t c o r r e l a t e s w i t h t h e capacitance
t r a n s i e n t r e s u l t s i n which a broad peak a t H(0.35)
d f t e r 900°C anneal /lo/.
C6-70 JOURNAL DE PHYSIQUE
