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Mo - MODIFIED AMORPHOUS Ge : ELECTRICAL TRANSPORT AND STRUCTURE
A. Devenyi, C. Rusu, A. R. Belu, R. Manaila
To cite this version:
A. Devenyi, C. Rusu, A. R. Belu, R. Manaila. Mo - MODIFIED AMORPHOUS Ge : ELECTRICAL
TRANSPORT AND STRUCTURE. Journal de Physique Colloques, 1981, 42 (C4), pp.C4-1089-C4-
1092. �10.1051/jphyscol:19814239�. �jpa-00220870�
MO
-
MODIFIED AMORPHOUS Ge : ELECTRICAL TRANSPORT AND STRUCTUREA. Devenyi, C. Rusu, A. Belu and R. Manaila
I n s t i t u t e of Physics and TeehnoLogy of Materials, Bucharest, P.O. Box MG-7, Romania
P b s t r a c t . - The e l e c t r i c a l r e s i s t i v i t y , e l a s t o r e s i s t i v j t y and s t r u c t u r e measurements on M - m o d i f i e d amorphous C e f i l m s 5 " 0 , C e l - ~ ( 0 . 0 1 1 ~ 5 0 . 4 8 ) show t h a t i n c r e a s i n n t h e m e t a l concen- t r a t i o n a r a d u a l l y m o d i f i e s t h e s e n - i c o n d u c t i n a c h a r a c t e r and c o v a l e n t b o n d i n a , c h a r a c t e r i s t i c f o r a-Ge, t o w ~ r d s a more m e - t a l l i c b o n d i n a t y o e
.
The ourwose o f t h e p r e s e n t p a p e r i s t o s t u d y t h e i n f l u e n c e o f m e t a l atoms (b'o) on t h e t r a n s v o r t l s r o o e r t i e s and s t r u c t u r e o f amor- qhous G e (a-Ge) f i l m and t o d e r i v e i n q o r m a t i o n a b o u t t h e way t h e y i n t e r a c t w i t h t h e a-Ge m a t r i x .
E l e c t r i c a l r e s i s t i v i t y , e l a s t o r e s i s t a n c e and X-ray d i f f r a c t i o n measurements w e r e c a r r i e d o u t on poxGel-x homoneneous
,
a ~ o r n h o u s f i l m s( t h i c k n e s s t'k2000 W ) f o r 0.015xSO. 48, i n comnarison w i t h a-Ce.
The f i l m s w e r e o b t a i n e d by c o e v a w o r a t i o n from two i n d e b e n d e n t l y c o n t r o l l e d e l e c t r o n i c a u n s i n a vacuum b e t t e r t h a n 5 . 1 0 - ~ t o r r . The d e p o s i t i o n r a t e s w e r e a b o u t 10
B / s
and t h e c o m ~ o s i t i o n p a r a m e t e r X was v a r i e d by c h a n a i n a t h e d e l s o s i t i o n r a t e o f $ 0 . The f i l m s w e r e e v a p o r a - t e d on f u s e d s i l i c a s u b s t r a t e s a t 50°c and o r o v i d e d w i t h ~ r e v i o u s l y d e p o s i t e d ( a t 5 5 0 0 ~ ) M O e l e c t r o d e s . The f i l m t h i c k n e s s e s w e r e c o n t r o l - l e d by a S l o a n q u a r t z c r y s t a l t h i c k n e s s m o n i t o r and F i n a l l y me3sured by t h e T o l a n s k y method. The bfio c o n t e n t was checked by m i c r o n r o b e and X-rav f l u o r e s c e n c e a n a l v s i s .-
1. E l e c t r i c a lrans sport
Prom f i a . 1 it can b e s e e n t h a t w i t h i n c r e a s i n n PO c o n c e n t r a t i o n , t h e e l e c t r i c a l r e s i s t i v i t v c d e c r e a s e s r a l s i d l v UD t o x'W.20. A t h i q h e r
c o n c e n t r a t i o n s , t h e r e i s a s l o w e r d e c r e a s e o f p . The same b e h a v i o u r was o b s e r v e d w i t h o t h e r me- t a l - m o d i f i e d a - r e s y s t e m s [l-51
.
P i n . 1 . "he e l e c t r i c a l r e s i s t i v i t v a t 300 K o f a-MoxGel-, f i l m s a s a 'unction o f X.
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L.. - - Fig.2 shows t h a t t h e s e n i c o n d u c t i n a be-
h a v i o u r o f a-Ge i s p r e s e r v e d f o r 0 1 ~ 5 0 . 1 6 , b u t
I O - ~ --__
t h e s l o n e o f l o o D v s . l o 3 / ~ n l o t d e c r e a s e s w i t h
0 0 5 lx/Mol i n c r e a s i n a X . The a c t i v a t i o n e n e r a y AE was de-
t e r m i n e d a s a f u n c t i o n o f T by n u m e r i c a l d i f f e - r e n t i a t i o n o f t h e as-measured p v a l u e s and i s b r e s e n t e d i n f i a . 3 . The r e s i s t a n c e measurements w e r e p e r f o r m e d a t v e r y s m a l l t e m o e r a t u - re i n t e r v a l s ATS0.3 K . T i a . 3 shows t h e e x i s t e n c e o f two t v n e s o f AE(T) d e p e n d e n c e s : a. a c t i v a t i o n e n e r a i e s AE c l o s e t o t h e AE,(T) f o r a-C*, w i t h AE>kT b u t AE<AE a and b . a c t i v a t i o n e n e r a i e s much below t h o s e o f a-Ge, v i t h AEskT. Tor the f i r s t t y p e o f c u r v e s , X - h i c h c o r - r e s o o n d t o x < 0 . 0 7 5 , t h e Mott t y n e h o p o i n o c o n d u c t i o n , c h a r a c t e r i s t i c f o r a-Ce i n t h e l o w e r T r a n o e i s o r e s e r v e d , b u t i t i s s h i f t e d t o
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19814239
JOURNAL DE PHYSIQUE
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300 LOO 500 600 TIKI F i n . 2 . The r e c i p r o c a l F i n . 3. l o a AF v s . l o n T r i n . 4 .n i n c r e a s e a t t e r r o e r a t u r e d e n e n d e n - 0 1 o t f o r a-'40x('el a n n e a l i n n f o r " ~ , C e l - ~
ce o f o f o r vogrel-, i n c o m a ~ r i s o n w i t h f i l m s . P n n e a l i n a t i r e
f i l ~ s i n comparison a - r e
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a t e a c h m was 30 min.w i t h a - c e .
h i n h e r T when Mo stops a r e adc7ed. "he w e a k e r T deoenirence o f AE i n t h e l o w e r T r a n n e f o r X-0.02 and x=0. p 3 i n f i i c a t e s t h a t Mo i n t r o d u c e s an i m n u r i t v l e v e l a t C=0.049-0.059 eT7.Por h i n h e r rJo c o n c e n t r a t i o n s
( ~ 2 0 . 9 7 5 ) ~ t h e v a l u e s AFskT c o u l d b e e x n l a i n s d b y a d o m i n a n t c u r r e n t m e c h a n i s
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a s t h a t a n n l i e d i n t h e c a s e o f o t h e r m e t a l - d i e l e c t r i cf i l m s
A ~ n e a l i n f r i n c r e a s e s t h e r e s i s t i v i t y o f F"oxrel,, f i l l r s w i t h x50.16 l i k e i n P - C ~ , l ~ t h i s e f f e c t d i m i n i s h e s w i t h i n c r e a s i n a Fflo t
c o n t e n t , a s c a n b e s e e n f r o m f i a . 4 .
F i n . 5. The r o o n t e m n e r a t u r e e l a s t o r e s i s - t i v e c o e f f i c i e n t s k L ( l o n n i t u d i n a l ) ,kT
( t r a n s v e r s s l ) v s . p F o r a s - 6 e a o s i t e d (AD) a n ? a n n e a l e d a t 550 K VoXCel-, f i l m s a n d t h e c o r r e s w n n d i n c r c o n c e n t r a t i o n X.
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-L i n c r e a s i n a X from t h e l a r a e n e n a t i v e va-
l u e s , c h a r a c t e r i s t i c f o r a - r e , t o w a r d s p o s i t i v e o n e s , c h a r a c t e r i s t i c f o r m e t a l - l i c % F i l m s . "he t r a n s i t i o n f r o m t h e
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a m o r a h o u s - t v p e b e h a v i o u r t o t h e m e t a l l i c - 8 - 0 k , 550K o n e t a k e s v l a c e a l r e a d y a t low vo c o n c e n -
n k T 550K t r a t i o n s . A t x=0.04 k ~ a n d k~ b e c o n e po- -10 - v X at.% s i t i v e and f o r W O . 2 0 t h e r e i s n o n o t i -
'0,
c e a b l e chancre o f k w i t h t h e "o c o n c e n t r a -\ t i o n , t h e r a t e r i a l h a v i n n f r o m t h i s p o i n t - 12
,
X at% o f v i e w a m e t a l l i c c h a r a c t e r . A n n e a l i n o - 1.4 \ c o e f f i c i e n t s o f t h e f i l m s t o w a r d s more-c n e n a t i v e o n e s , a s i t i s a l s o t h e c a s e i n 50 a-Ge. P S was n o i n t e d o u t i n 171, i n c r e a - - 16 AD sincr N ( E F ) i n a-Ge b r i n o s a b o u t a n e x t e n -
s i o n o f t h e pflott-tyne c o n d u c t i o n r e a i o n
P I 11
- l 8 - L -2 C +2 +Llogp 0 t o w a r d s h i n h e r T , a s w e l l a s a n i n c r e a s e
(,c,) o f k L and k ~ . The sarne b e h a v i o u r c a n b e
2 . nton-ic s t r u c t u r e and b o n d i n a . X-ray d i F f r a c t i o n showed t h e MO, (a-"e) f i l m s t o b e amornhous. The 3 i . F f r a c t i o n n a t t e r n s w e r e measu- r e d w i & h ' r u ~ ~ r a d i a t i o n f o r t h e filrrs w i t h x=0. n4, 0 . 1 9 , 0 . 4 3 and 0.48.
The c o n t r i b u t i o n O F t h e f u s e d s i l i c a s u b s t r a t e was s u b t r a c t e d by a con-nuter ~ r o c e d u r e , u s i n a an e s t i n - a t e d u t v a l u e ( p = l i n e a r a b s o r p t i o n c o e f f i c i e n t )
.
F i n . 6 d i s n l a v s t h e i n t e r f e r e n c e f u n c t i o n s F ( k ) = (1,,-<f9 / < f > 2 (k=4rsint?/X'
.For t h e l o w e s t c o n c e n t r a t i o n (x=0. 0 4 , f i q . l a ),
t h e i n t e r f e r e n c e f u n c t i o n r e n r o d u c e s t h e f e a t u r e s o f p u r e a-CR [8], w i t h e x t r a d e t a i l s a t 4.6 and 5 . 8 $-l, which c o u l d b e due t o n u c l e i of Ge-PO comoounds.
I n c r e a s i n c r t h e MO c o n c e n t r a t i o n b r i n a s a b o u t s i c m i f i c a n t a l t e r - a t i o n s o f t h e i n t e r f e r e n c e att tern t h e F i r s t ~ e a k a t 1 . 9 d e c r e a - s e s
,
w h i l e t h e s e c o n d one a t 3 . 4 ~ - ~ s h i f t s t o w a r d s s r n a l l e r k . A l s o , an i n t e n s i t v r i s e i s t o be n o t i c e d a t k = 3 . 6 , 4.8 and 5 . 88-1
f o r t h e h i n h e r X v a l u e s . The s a r r n l e w i t h x=0.19 mav b e s l i a b t l v inhomoaeneous, x h i c h would a c c o u n t f o r t h e b r o a d e n e d neak a t 3.18
1. The n o s i t i o n s and h e i a h t s of <he f i r s t F ( k ) r n a x i ~ a a r e c o l l e c t e d i n t a b l e 1.T a b l e 1. P o s i t i o n s a n d h e i a h t s o f t h e p ( k ) ~ a x i m a i n %,(a-Ge)l-,
X k l F1 k2 ( 8 - l ) R G ~ ,
(8)
0.04 1.92 1 . 1 7 3.42 2.45
0.19 1 . 9 2 0 . 2 5 3.13 2.64
0.43 1.80 - 9 . 3 2 2 . 9 1 2.88
0 . 4 8 1.80 -0.40 2.85 2.93
F i n . 5 . E x n e r i m e n t a l F ( k ) o f MO,
( a - + ) f i l m s w i t h x = O . O 4 ( a ) , 0.19 ( b { ; ~ . 4 3 ( C ) and 0 . 4 8 ( d ) .
These chancres a r e c h a r a c t e r i s t i c f o r m o s t M-(a-Ce,Si) systerns(M=Cu
C23
,
Fe [3,4],
Aup]
) and n o i n t t o a n r o f o u n d a l t e r a t i o n o f t h e s h o r t - r a n a e o r d e r w i t h i n c r e a s i n a Y con- c e n t r a t i o n . They c a n b e a c c o u n t e d f o r i n t h e frame o f a new s t r u c t u - r a l model f o r t h e M- (a-Ge) s y s t e m s[g]
,
w h i c h a l l o w s t h e M atoms t o F i l l t h e l a r a e r emoty s p a c e s , i n - h e r e n t t o a n v CRN model o f a-Ce[l01 .
A subsecrue'nt r e l a x a t i o n o f t h e mo- d e l i s ~ e r f 0 r F e d w i t h r e s p e c t t o t h e bond d e f o r m a t i o n e n e r q , u n d e r h a r ~ o n i c b o n d - s t r e t c h i n a and bond- b e n d i n n o o t e n t i a l s and u s i n a a L e n n a r d - J o n e s law f o r t h e M-Ce i n - t e r a c t i o n . T h i s r e l a x a t i o n l e a d s t o a d e n s e r n a c k i n a o f t h e F' and Ge a t o m . The c o r r e s o o n d i n a i n t e r f e r e n - c e f u n c t i o n c o r r e c t l y a c c o u n t s f o r t h e metal-inc'uced c h a n a e s , a s was
!shown i n [g] f o r t h e Cu,(a-Ge)l-, a l l o v s i n v e s t i a a t e d i n ~ 2 ]
.
A model c o n t a i n i n a a t o t a l o f 198 a t o m was u s e d i n t h e
resent work, c o r r e s p o n d i n u t o a MO
JOURNAL DE PHYSIQUE
REFERENCES
c o n c e n t r a t i o n o f x d . 2 2 .
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Tn t h e model F ( k ) , t h e p o s i t i o n o f1. CHOPRA K.L, and NATH P . , p h v s . s t a t . s n 1 . ( a ) 33 (19761 333
2. MOWAK H.,T., LEITZ H . and BUCKFL W . , ~hvs.st~.sol.(a)49(1978)73 3. UEMVRA O., SUZIJKI Y . a n d SPFOW T . , ~ h y s . s t a t . s o 1 . (a1417i9771417 4. MANGTN P . , \"AFCHAL C . , RODMACO B . and JANOT C. ,Phil.w"aa.36 (19771643 5. MANGIN P.
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DAUL W. and CONNEL G . \ . N . , F d ~ . P h v s . ~ ( 1 9 7 3 ) 5 8 1 9. YANATLA R. and DETTNYI A .,
p h y s . s t a t . s o 1 . (h) 102 (1980) 6 1 10. GRTCOROVICI R . , J . W O ~ - c r y s t a l l i n e ~ o l i d s 35-3-1980)116711. GRTGOROVICI F . , MANAILA R . , POPFSCU M. and STANESCU C . , FIP Conf.
P r o c .
2
( 1 9 7 4 ) 200.h e s e c o n d i n t e r f e r e n c e peak a t k2=3.4 i s m a i n l y d e t e r m i n e d by t h e e q u i l i -
1
/*
briurn d i s t a n c e s C e - G e (FGG) a n d Ge-No (RGM).
-
/ / R e l a x a t i o n p r o c e d u r e s c a r r i e d o u t w i t h/ t h e c r v s t a l v a l u e R ~ G = ~ . ~ S
8
d i d n o t s i v e/ / /
s a t i s f a c t i o n . I n s t e a d , i t was f o u n d t h a t
1 an i n c r e a s e o f RGG c o u l d r e ~ r o d u c e f a i r l y w e l l t h e s h i f t o f t h e k2 peak t o w a r d s
-
/ s m a l l e r k . R e l a x a t i o n w i t h d i f f e r e n t R c , ~/ / v a l u e s showed t h a t t h e D ~ O ~ U C ~ R ~ c , . ~ G c , i s
1 n r a c t i c a l l y a c o n s t a n t = 8 . 4 5 ( k f G = o o s ? t i o n
,
/ bO o f t h e s e c o n d ~ e a k i n t h e art a 1 G e G e F(k) ).
nn t h i s b a s i s , t h e k ~ ~ v a l u e c a n2.L0
b e e s t i m a t e d and a m o d e l l i n a o f t h e e x u e r i -O2 O4
m e n t a l F ( k ) n e a r a t k 2 becomes p o s s i b l e , f o r d i f f e r e n t RCG v a l u e s and RGM=2.658.
T h i s was done by r e c o n s t r u c t i n a t h e ueak F i a . 7 . E n u i l i b r i u r n Ge-Ge from t h e n o d e l p a r t i a l F ( k ) I s . F o r i n c r e a - d i s t a n c e v s . e l e c t r o n den- s i n a X , t h e m o d e l l i n n r e q u i r e s i n c r e a s i n a s i t y v a r i a t i o n ( f r o v mo- R ~ G v a l u e s ( t a b l e 1)
.
R e l a x a t i o n o f t h e d e l l i n a s t u d i e s ) . *:MO model w i t h n r o p e r RG 'S a l s o r e ~ r o d u c e s(a-Ge) l-x, X : C U ~ ~ (a-GeTi7 t h e d e c r e a s e i n m a m f t u d e o f t h e peak a t C 2 , j
,
o : r e I I I , A:GeIV 1g.
k l .The i n c r e a s e o f t
5,
e RrG v a l u e s w i t h MO c o n c e n t r a t i o n i s i n d i c a - t i v e o f an o v e r a l l " ~ e t a l l i z a t i o n " nf t h e s y s t e m . I n t r o d u c i n a MO atoms i n t o t h e a-Ge m a t r j x seems t o modifv t h e a e n e r a l c h a r a c t e r o f t h e bon- d i n a , from a c o v a l e n t t o w a r d s a more m e t a l l i c one. These f i n d i n a s a r e i n f u l l a a r e e ~ e n t w i t h t h e e l a s t o r e s i s t a n c e and a c t i v a t i o n e n e r a y re- s u l t s r e p o r t e d above.Conoer was f o u n d t o c a u s e a s i m i l a r b u t s m a l l e r e f f e c t [g] on t h e RG v a l u e s i n t h e amomhous c ~ , ( a - G e ) ~ - a l l o v s . F i a . 7 c o l l e c t s t h e d a t a o n t h e FGG i n c r e a s e , i n d u c e d h v a f l o v i n a w i t h Fo a n d Cu, i n c o m ~ a r i s o n w i t h t h e e f f e c t o f i n c r e a s e d e l e c t r o n d e n s i t v p i n t h e c r v s t a l l i n e h i a h - n r e s s u r e Dolyrnor~hS GeTT7: and GsIV E l l .
.
A s c a n b e s e e n , t h e t o t a l e l e c t r o n d e n s i t v seems t o i n f l u e n c e s t r o n a l v t h e na- t u r e o f t h e b o n d i n a i n a l l t h e s e s y s t e m , c a u s i n g a " m e t a l l i z a t i o n "a t h i a h e r o v a l u e s .
