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PHOTO AND ELECTROCHEMICAL DOPING IN Ge-BASED CHALCOGENIDES
S. Rajagopalan, K. Solomon Harshavardhan, Bhanwar Singh, K. Chopra
To cite this version:
S. Rajagopalan, K. Solomon Harshavardhan, Bhanwar Singh, K. Chopra. PHOTO AND ELECTRO-
CHEMICAL DOPING IN Ge-BASED CHALCOGENIDES. Journal de Physique Colloques, 1981, 42
(C4), pp.C4-911-C4-914. �10.1051/jphyscol:19814198�. �jpa-00220825�
JOURNAL DE PHYSIQUE
CoZZoque C4, suppZdment au nO1O, Tome 42, octobre 1981 page C4-911
PHOTO AND ELECTROCHEMICAL DOPING IN Ge-BASED C H A L C O G E N I D E S
S. Rajagopalan, K. Solomon Harshavardhan, Bhanwar Singh and K.L. Chopra Department o f Physics, Indian I n s t i t u t e o f Technozogy, DeZhi,
Neu DeZhi 110 016, India
A b s t r a c t : Photo and e l e c t r o c h e m i c a l doping of o b l i q u e l y d e p o s i t e d Ge-chalcogenide f i l m s have been s t u d i e d by AES/XPS teohniques. The e f f e c t of e l e c t r o c h e m i c a l a d s o r p t i o n and photodoping on t h e o p t i c a l t r a n s m i t t a n c e i s presented. The atomic c o n c e n t r a t i o n depth p r o f i l e s of A g - s e n s i t i z e d amorphous Ge and Ge Se f i l m s have been e s t a b l i s h e d . The chemical state o f
A P % ~
? I d 5 a s s o c i a t e d c h e m i c a l changes i n t h e c h a l c o g e n i d e brought about by photo and e l e c t r o c h e m i c a l d o p i n g p r o c e s s e s have been i d e n t i f i e d . Some d e t a i l s of t h e b u i l t - i n columnar s t r u c t u r e and s t r e s s e s i n o b l i q u e l y d e p o s i t e d f i l m s have b e e n r e v e a l e d by t h e p r e s e n t study.I n t r o d u c t i o n : I t h a s been w e l l e s t a b l i s h e d t h a t t h e c h a l c o g e n i d e g l a s s e s on e x p o s u r e t o band gap i l l u m i n a t i o n undergo v a r i o u s s t r u c t u r a l (1,2,3), o p t i c a l
(4-7) and e l e c t r o c h e m i c a l (8.9) t r a n s f o r m a t i o n s . Of a l l t h e photoinduced e f f e c t s r e p o r t e d i n t h d l i t e r a t u r e (1-9) t h e photoinduced d i f f u s i o n of metals i n t h e s e g l a s s e s h a s been widely r e c o g n i s e d due t o i t s p o t e n t i a l a p p l i c a t i o n s i n t h e f i e l d of imaging technology. The photoinduced d i f f u s i o n of t h e adsorbed m e t a l s i n t o t h e c h a l c o g e n i d e g l a s s e s i s a c h a r a c t e r i s t i c phenomenon caused by p h o t o e x c i t a t i o n (10). The e l e c t r o c h e m i c a l doping and o t h e r r e l a t e d pheno- mena i n n o m a l and o b l i q u e l y d e p o s i t e d amorphous Ge Se films have been e x t e n s i v e l y s t u d i e d i n o u r l a b o r a t o r y by Sin& e t a 3 (3571-14) and it h a s been e s t a b l i s h e d t h a t o b l i q u e d e p o s i t i o n enhances t h e e l e c t r o c h e m i c a l doping.
Though t h e k i n e t i c s of t h e e l e c t r o c h e m i c a l a d s o r p t i o n p r o c e s s have been s t u d i e d by some workers (15) i n t e r n s of t h e changes i n r e s i s t i v i t y and t r a n - s m i s s i o n , t h e photo and e l e c t r o c h e m i c a l doping p r o c e s s e s have n o t been expla- i n e d i n d e t a i l . F u r t h e r , t h e d i s t r i b u t i o n of t h e metal, i n t h e volume of t h e f i l m and i t s chemical s t a t e a r e f a r from c l e a r . Our p r e s e n t s t u d i e s on photo and e l e c t r o c h e m i c a l doping e f f e c t i n normal and o b l i q u e l y d e p o s i t e d amorphous
f i l m s have thrown l i g h t on t h e u n d e r s t a n d i n g of t h e fundamental Ag photo and e l e c t r o c h e m i c a l doping i n Ge-based c h a l c o g e n i d e g l a s s e s .
The e x p e r i m e n t a l d e t a i l s f o r vacuum d e p o s i t i o n of t h e f i l m s , and s u b s e q u e n t e l e c t r o c h e m i c a l a d s o r p t i o n and photodoping of m e t a l s , have been d e s c r i b e d elsewhere b y Singh e t a 1 (3,14). The photoinduced d i f f u s i o n s t u d i e s through AESand XPS t e c h n i q u e s have been c a r r i e d o u t w i t h Super SAM/ESCA I n s t - rument, PHI 590 A-1 0.
R e s u l t s and d i s c u s s i o n : The depth p r o f i l e s of Ag-sensitized normal (00) and o b l i q u e l y (BOO d e p o s i t e d amorphous a r e shown i n Pig.1 (a&b).
I t i s c l e a r t h i t M i s replaced by Ag, completely u p t o 100 a & i n t h e c a s e of 80° f i l m s and, p a r t i a l l y , u p t o 65 a'$ i n 00 f i l m s . An oxygen p r o f i l e h a s appeared a f t e r the A g - s e n s i t i z a t i o n p r o c e s s which f o l l o w s t h e Ge p r o f i l e .
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19814198
JOURNAL DE PHYSIQUE
SPUTTER ETCHING TIME I minl SPUTTER ETCHING TIME Imm)
Fig. 1 : Depth p r o f i l e of Ag-sensitized amorphous Ge f i l m s (0°&800).
Replacing Ge by Se ( a s i n Geo alSeo 5) h a s d r a s t i c a l l y decreased the electrochemical a d s o r p t i o n of Ag
6
ch la about 2 at$ only upto 100A thickness i n t h e case of 00 deposited f i l m s and about 20 a'& i n t h e case of 800deposited films. On i l l u m i n a t i o n , Ag d i f f u s e s ' decreasing t h e concentration gradient a s , P o w n i n c u r v j b (photon flux-JIOWphotons om-l) and curveho hot on
f l u x u1 0 photons cm- ) of figure2, u n t i l t h e c o n c e n t r a t i o n gradient becomes zero t o give a c o n s t a n t p r o f i l e .
Fig.2: Depth p r o f i l e of Ag-sensitized amorphous Ge0.25Se0.75 f i l m s (00).
Se / 60 -
-
sz
0
I n t h i s condition, t h e f i l m i s i n s o l u b l e in a n a l k a l i n e medium. This s e l e c t i v e chemical e t c h i n g behavior with such a high c o n t r a s t ( c l o s e t o lo@) make these f i l m s a s inorganic r e s i s t m a t e r i a l s f o r h i & r e s o l u t i o n l i t h o g r a p h i c applica-
t i o n s . The r e l a t e d changes i n t h e r e l a t i v e c o n c e n t r a t i o n p r o f i l e s of Ge and Se a r e too small ( l a % ) t o be d e t e c t e d by AES/ESCA.
,-
40- z
W
Y r
S
The atomic concentration p r o f i l e s of 800 deposited Ge Se f i l n s under electrochemical and pho todoping conditions a r e sh0w8'g f P$?e I t 3 (a&b)
.
is c l e a r t h a t i n t h e case of 800 deposited f i l m s , t h e amount of e l e c t r o - chemical adsorption/doping is about
5
t o 6 times h i g h e r than t h e 00 deposited f i l m s , and i n c r e a s e s towards t h e f i l m - s u b s t r a t e i n t e r f a c e . F u r t h e r , a s the atomic c o n c e n t r a t i o n of Ag i n c r e a s e s along the depth, the G e concentrationGe
2 4 6 1
SPUTTER ETCHlNGllME ( m m )
SPUTTER ETCHING TIME lmnn)
SPUTTER ETCHING TIME(min1
F i g . 3: Depth p r o f i l e o f A g - s e n s i t i z e d 80° Ce-Se f i l m s .
g o e s downj Se p r o f i l e r e m a i n i n g i n t a c t a s t h a t f o r undoped f i l m s . On e x p o s u r e Ag d i f f u s e s o u t t i l l no c o n c e n t r a t i o n g r a d i e n t of Ag e x i s t s t h r o u g h o u t t h e f i l m . The Ge p r o f i l e r e m a i n s p r a c t i c a l l y unchanged a n d t h e Se p r o f i l e shows a s l i g h t i n c r e a s e t o w a r d s t h e s u b s t r a t e a f t e r photodoping.
F o r c o m p r e h e n s i v e i n t e r p r e t a t i o n and c h e m i c a l s t a t e i d e n t i f i c a t i o n Of t h e Se-Ge:Ag f il2s a f t e r p h o t o a n d e l e c t r o c h e a i c a l d o p i n g , t h e e x a c t p e a k p o s i t i o n a s w e l l a s t h e w i d t h (F'VIIIM) of Se 3d, Ce 3d a n d Ag 3 d 5 l 2 1 i n e s h a v e b e e n tabu- l a t e d a l o n g w i t h t h e a v a i l a b l e s t a n d a r d s .
S t a n d a r d 800 Se-Ge 800 Se-Ge:Ag
L i n e B i n d i n g i 3 i n d i n g a i n d i n g
J n e r g y F'VHIli Energy F\MM Energy FXIM
P o s i t i o n ( e ~ ) P o s i t i o n ( e ~ ) P o s i t i o n ( e ~ )
-
( e v ) ( e v ) ( e v >Ce 3d 28.95 1.47 31.6 1.9 30.65 1.9
- - --
Though t h e Ag peak p o s i t i o n c o i n s i d e s w i t h t h e s t a n d a r d Ag v a l u e , Se 3d p e a k p o s i t i o n h a s d e c r e a s e d from 55.3 t o 54.3 eV a f t e r Ag doping. A l s o , t h e r e i s a c o r r e s p o n d i n g p e a k s h i f t in Ge 3d f r o m 31.6 t o 3C.65 eV. T h e s e c h e m i c a l s h i f t s may be a t t r i b u t e d t o t h e p r e s e n c e of Ag2Se, Ag c l u s t e r p r e c i p i t a t i o n and o t h e r complexes l i k e Ag-Ge-Se a f t e r Ag doping. I n d e e d , t h e s e p h a s e s h a v e been
c o n f i r m e d by o u r TEI4 s t u d i e s .
The e l e c t r o c h e m i c a l a d s o r p t i o n p r o c e s s , which i s a n e l e c t r o c h e m i c a l d i s - p l a c e m e n t t y p e of r e a c t i o n , i n v o l v e s o x i d a t i o n o f Ge atoms by m e t a l ( ~ g ) i o n s b y c h a r g e t r a n s f e r t i l l t h e e q u i l i b r i u m e l e c t r o c h e m i c a l p o t e n t i a l i s a t t a i n e d between t h e s e m i c o n d u c t o r s u r f a c e a n d t i e e l e c t r o l y t e . The p r e s e n c e of GeO h a s b e e n o b s e r v e d by XPS a n a l y s i s f o r Ge 3d s h e l l o f amorphous Ge f i l m s b e f o r e a n d 2 a f t e r e l e c t r o c h e m i c a l doping. A l s o , i t is t o be p o i n t e d o u t t h a t f r e e Se i s r e l e a s e d when Ag r e p l c e s Ge by t h e e l e c t r o c h e m i c a l d i s p l a c e m e n t r e a c t i o n . But o n l y d u r i n g p h o t o e x p o s u r e , t h e f r e e Se d i f f u s e s t o w a r d s t h e s u b s t r a t e , a s s e e n f r o m t h e Se p r o f i l e of 8 0 ° d e p o s i t e d Ge Se f i l m s a f t e r p h o t o doping. On e x p o s u r e t o band gap i l l u x i n a t i o n , t h e % ? & s ~ d 5 0 f Ag o c c u r s t o homogenize t h e Ag i n c h a l c o g e n i d e n e t w o r k u n t i l a n u n i f o r m p r o f i l e i s a t t a i n e d forming
C 4 - 9 1 L JOURNAL DE PHYSIQUE
c o z p l e x e s o f t h e t y p e Ag-Ge-Se p l u s A G ~ S ~ a n d Ae; c k l s t e r p r e c i p i t a t i o n .
',"he e n h a n c e d e l e c t r o c h c r ~ i c o l d o p i n g i n SO0 d e p o s i t e d f l l n s c a n b e a t t r i b u - t e d t o t h e p r e s e n c e o f c o l u 3 n a r i n t e r f a c i a l r e g i o n s : r i t h a s s o c i a t e d v o i d s e n d d a n g l i n g b o n d s w h i c h a c t a s d i f f u s i o n p i p e s . T h e i n v e r s e p r o f l l e o f ~g ( i n c r e a - s i n g Ag toi.:ards t h e s u b s t r a t e ) may b e due t o t h e i n f l u e n c e o f t h e b u i l t - i n s t r e s s e s a t t h e f ~ l u - s u b s t r z t c i n t e r f a c e .
O u r f u r t h e r s t u d i e s o n x e t n l d o p i n g h a v e e s t a b l i s h e d t h a t t h e a e t a l d o p i n t ; d e c r e ~ s e s by 2.5 a n d 1G i n c a s e o f Cu a n d Xu, r e s p e c t i v e l y e n d i s p r a c t i c a l l y
z e r o i n t h e c a s e o f A l .
C o n c l u s i o n s : 1. T h e p r e s e n c e o f oxygen, o x i d e f o . ~ a t i o n in a-3orphous Ge f i l n s d e p o s i t e d c l o s e t o n o r n n l i n c i d e n c e a n d t h e c o x p l e t e c o n v e r s i o n of G e to Ag i n t h e c a s e o f 8 C o d e p o s i t e d f i l n s a d d t o t::e u n d e r s t a n i i n g of t h e e l e c t r o c h e c i c a l a d s o r p t i o n p r o c e s s a n d i t s r e a c t i o n a e c h a n i s z .
2. T h e a h o t o i n d u c e d d i f f u s i o n o f Ag n t t a i n s s a t u x t i o n , p r o d u c i n g a homogeneous A g p r o f i l e , f o r m i n g A&-Ge-Se c o n p l e x a a d Ag2Se, w h i c h a r e i n s o l - u b l e i n a l k a l i n e oediusl.
3. The c o l u ~ n a r s t r u c t u r e a n d t h e f i l y - s u b s t r a t e i n t e r f a c e a r e r e s p o n s i b l e f o r t h e u n u s u a l A g p r o f i l e p r e s e n t i n 800 'A-Se:.kg f i l o s . R e f e r e n c e s :
1. S h i r n i z u , I . and F ? . i t z s c h e , 3.. J.A?pl.Phy~. 4J, (1 9 7 6 ) , 2 9 6 9 .
2. Tanaka,K.and Ohtsukn,Y., 'Thin S o l i d F i l m s , $3, ( 1 9 7 3 ) , 1 7 ; J.Appl.Phys.
a,
( 1 9 7 8 ) , 6 1 3 2 .3. Bhanlrar S i n c h , R a j a g o p a l a n , S . , Shat,P.K., P a n d y a , D.E. a n d Chopra,%.L., S s l i d S t a t e C o ~ r u n .
3,
( 1 9 7 9 ), 1 ~ 7 .4. d e N e u f v i l l e , J.P., i n @ ? t i c a l F r o p o r t i e s o f S o l i d s - R e c e n t Develope;:cnts, e d i t e d by .jeraphin,B.O. ( I10:th-Liolland, A m s t c r d l a , 1 3 7 5 ).
5.
d e N e u f v i l l e , J.P., ..osn,S.C. a n ? vvst-iinsky, 3.2. J.9on-Crys:. S o l i d s2,
0 9 7 4 ) , 1 9 1 .6. 'isr~icn,K., h?pL.Yhys.Lett.,&, ( 1 9 7 5 j,243.
7. Ksnezan,s.~.?odob.na,J.nnci Ze?el,J.t{, Z.kppl.Phys, fg, ( 1 9 7 ~ i 4 6 6 3 .
U. Jts';gi,Y.an.? i e ? L b u t s ~ , ; . , B p p l . P h y s . i e t t .
a
( 1 3 7 5 ),5:.8.9. Chan;,l.~..j. 2nd ~ ! o u , T . : ~ . , O ~ ~ . C O E T T . U ~ . - ? ~ . , (1 97b ), 22,,, T h i n S o l i d P i l r ~ s
2.
( 1 9 7 8 ),463.1 0 . Kokado,lf. S h i n i z u , I . nnc! Inoue,E., J.Yon-Cryst. s o l i d s , & , ( 1 9 7 6 1131.
1 1 . Dhon:ar d i n & , R a j a g o p a l a n , 3 . . ah-t,F.P., Pnndya,D.X. a n d Chopra,;\'.L., J.::on-Cr:rst.dolids, x L J 6 , (1 38; ), 1 ~ 5 3 .
12. Rajagopal:ln,S., Bhanlrar S i n g h , Bhst,P.K.,Pnndya,D.K.and Chop?a,K.L., J.Appl.Phys.,
2,
( 1'379 j.489.1 3 , B h a n e a r S i n g h , A a j r g o p a l a n , ~ . a n d Choyra,X .L,J.l;?pl.Phya.
51,
(190;),1768.14. Rhan:;ar S i n g h , Chopra,K.L., J.Appl.fhys. ( ~ n P r c s s ).
15. Gold jchr:,idt,D. a n d h d x a n , P . S . , J . N o n - C r y s t . S o l i d s , 2 2 , (1 9 7 6 ), 229.
