THE ENHANCEMENT OF THE DARK CONDUCTIVITY AND PHOTOCONDUCTIVITY OF GD a-Si INTRODUCING O2, N2

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THE ENHANCEMENT OF THE DARK

CONDUCTIVITY AND PHOTOCONDUCTIVITY OF GD a-Si INTRODUCING O2, N2

Wen Xu, Zhong Sun, Zhong Wang, De Lee

To cite this version:

Wen Xu, Zhong Sun, Zhong Wang, De Lee. THE ENHANCEMENT OF THE DARK CONDUCTIV-

ITY AND PHOTOCONDUCTIVITY OF GD a-Si INTRODUCING O2, N2. Journal de Physique

Colloques, 1981, 42 (C4), pp.C4-695-C4-698. �10.1051/jphyscol:19814154�. �jpa-00220777�

T H E ENHANCEMENT OF T H E D A R K CONDUCTIVITY AND PHOTOCONDUCTIVITY OF G D a-Si INTRODUCING 02, N2

Uen Yuan Xu, Zhong Lin Sun, Zhong Pang Wang and De Lin Lee Department ^of Physics, Nankai University, Tian ji n

ABSTRACT. T h i s p a p e r d e a l s w i t h u s i n g O2 o r N2 g a s as doping m a t e r i a l s of A - s i . A conspicuous enhancement of d a r k conduc- t i v i t y od and p h o t o c o n d u c t i v i t y 0 of A - s i was found by indu- c t i n g a s u i t a b l e amount of O2 o r ph N2 d u r i n g t h e p r o c e s s o f glow discharge decomposition of silane. The difference of their activation energies of these samples were compared. An infrared spectra analysis and field effect measurements of these A - s i films were made and a tentative dicussion given.

INTRODUCTION: The e l e c t r o n i c d e n s i t y of s t a t e s i n GD -si f i l m s h ve corn a r a t i v e l y loii v a l u e of t h e o r d e r of magnitude 10lbi-- 1 0 ~ 7

_-7

-3

e v near midgap, ( 1 ) t h e s e t y p e s of f i l m s can be doped N t y p e o r P t y e. T h i s h a s a l r e a d y been r e p o r t e d by many r e s e a r c h groups ( 2 )

( 3 7 . The o p t i c a l p r o p e r t i e s of A-.%:a:* f i l m s d e p o s i t e d from 02/siH4/

A r m i x t u r e s h a s r e p o r t e d ( 4 ) , b u t t h e i n f l u e n c e of t h e p r o p e r t i e s of GD A - s i f i l m s by s m a l l q u a n t i t y of 0 o r N h a s n o t y e t t o be understood.

I n o u r l a b o r a t o r y t h e o d and ^CJ of A - s i were enhanced by i n t r o - d u c t i n g a s u i t a b l e amount of O2 ph o r N2 and a n a p p r o p r i a t e r a t i o of N2/02 mixed g a s d u r i n g t h e growth of A - s i f i l m s , f o r 7 and 4 o r d e r s of magnitude was obtained r e s p e c t i v e l y . I t w a s found t h a t t h e a c t i v a - t i o n energy (Ec-Ef) and t h e e l e c t r o n i c d e n s i t y of s t a t e s n e a r a i d g a p of t h e oxygenic A - s i f i l m s remained n e a r l y t h e same a s t h a t of t h e undoping f i l m s . It was suspected t h a t ox gen might a l t e r t h e proper- t i e s of A - s i : H f i l m by o t h e r s c h o l a r s . (57. Our e x p e r i m e n t a l r e s u l t s might s e r v e as a s u b s i d a r y evidence t o show t h a t t h e b r i d g i n g 0 atoms i n t h e f i l m s c o u l d n o t o n l y d e c r e a s e t h e number of d e f e c t s and t h e r e b y i n c r e a s e t h e recombination l i f e t i n e , but might i n c r e a s e t h e inability of c a r r i e r s as well.

EXP3RI):BNTAZ D3TAILS: A c a p a c i t i v e l y coupled r a d i o f r e q e n c y glow d i s c h a r g e a p p a r a t u s was used t o f a b r i c a t e amorphous f i l m s of A - s i from SiH4. The n i t r o g e n , oxygen o r t h e i r n i x e d g a s was a d m i t t e d t o t h e r e a c t i o n v e s s e l through a s e p a r a t e l i n e t o a v o i d p r i o r r e a c t i o n w i t h t h e s i l a n e . Great p r e c a u t i o n were t a k e n i n t h e l e a k a g e of g a s f o r a l l v a l v e s and j u n c t i o n s of t h e a p p a r a t u s . The r e a c t i o n v e s s e l iias thorougly c l e a n e d each time we changed t h e r e a c t i n g gas. The g a s glow r a t i o (x/ SiH4, x=02, N 2 , o r t h e i r m i x t u r e s ) w a s a d j u s t e d by a n e e d l e valve. E l e c t r i c a l p r o p e r t i e s were measured on c o p l a n a r c e l l u s i n g AL and AU c o n t a c t e l e c t r o d e s with s p a c i n g v a r i e d i n t h e range of Imm-5mn. F o r IR t r a n s m i s s i o n s p e c t r a a n a l y s i s of t h e s e f i l m s , t h e y were d e p o s i t e d on h i g h r e s i s t i v i t y c r y s t a l l i n e C - s i wafers which were p o l i s h e d on b o t h s i d e . For f i e l d e f f e c t experiments, t h e A - s i was d e p o s i t e d on a q u a r t z e o r s i o 2 f i l m which was grown on t h e cry- s t a l l i n e S i wafers.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19814154

C4-696 JOURNAL DE PHYSIQUE

WSULTS AND DISCUSSION: E l e c t r i c a l p r o p e r t i e s ; F i g 1 . show t h e room t e m p e r a t u r e a d and u p h v e r s u s t h e flow r a t i o s r. Evidently, i n c r e a s i n g t h e flow r a t i o r , t h e od and o v a l u e s of y e i l d i n g f i l m s a r e l i n e a r l y

ph

Y l a lo+, ^T. %

F i g l . The dark c o n d u c t i v i t y Fig2. The d a r k c o n d u c t i v i t y and p h o t o c o n d u c t i v i t y v s f l o w of A - s i f i l m s VS TS.

r a t i o r. T =270°C. r.f power about 10 watts.

enhanced. It appears t o e x i s t a n e f f e c t i v e range from A t o A' f o r t h e flow r a t i o . When t h e flow r a t i o r i n c r e a s e d c o n t i n u a l l y o v e r t h e r a n g A ' , t h e excess of 0 o r N may i n d u c e a l o c a l new :;lorphology i n t h e network, t h e r e f o r e , t h e 0 and o suddenly droped. P i g 2.

shows t h e a d of A - s i f i l m s v s s u g s t r a b e @ m p e r a t u r e Ts. E v i d e n t l y , when t h e s u b s t r a t e t e m p e r a t u r e Ts is i n c r e a s e d , t h e d of oxygenic A - s i f i l m s a r e enhanced conspiouously. However, t h e r e a r e no obvious change i n t h e of t h e n i t r o g e n o u s A - s i f i l m s and t h e undoping f i l m s w i t h t h e s u b s t r a t e temp p e r a t u r e s . Adopting an a p p r o p r i a t e growing paramenters, t h e f o l l o w i n g r e s u l t s were o b t a i n e d as s h o ~ r n i n t:l.ble 1.

F i g 3. shows t h e od v s 10 '/T, f o r s e v e r a l samples. A l l e l e c t r i c measurement a r e made under an a p p l i e d e l e c t r i c f i e l d of 10~/mm.

These samples e x h i b i t e N-type behavior. The a c t i v a t i o n onergy

(Ec-Ef) of t h e oxygenic A - s i films a r e n e a r l y t h e undoped f i l m s .

It means t h a t t h e oxygen i n t h e i r network of A - s i f i l m does n o t induce any e v i d e n t new s t a t e s i n t h e gap. IIowever, t h e n i t r o - genous A - s i f i l m s do induce a l o c a l i z e d s t a t e below t h e conduction band edge Ec.

INFRARED SPECIRUY: F i g 4. shows t h e I R t r a n s m i s s i o n of t h i c k f i l m s of A-si:H:x, under t h e e f f e c t i v e doping c o n d i t i o n a s d i s c u s s e d above.

The I R s p e c t r a f o r oxygenic A - s i f i l m s e x h i b i t e a s m a l l peak a t 1100 cm -1

.

The I R s p e c t r a f o r n i t r o g e n o u s f i l m s exh.ibite a peak a t 8204360 c a

F i g 3 . The d a r k c o n d u c t i v i t y , P i g 4. The I R t r a n s m i s s i o n v s r e c i p r o c a l t e m p e r a t u r e s . s p e c t r a of A-si:H:x and The s u b s t r a t e t e m p e r a t u r e s C - s i . ~ , = 2 7 0 ' ~

T S = ~ ~ O ' C f o r all samples.

which a r e u s u a l l y a t t r i b u t e d t o t h e s i - N modes. The peak a t 2000-2100 cm-I, h a s been o r d i n a r i l y a t t r i b u t e d t o t h e s i - H , si-1l2 modes.

X l O O Q p r o nvbor

F i g 5. The I R t r a n s m i s s i o n s p e c t r a o f oxygenic A - s i films which w i t h d i f f e r e n t Ts

F i g 6. The l o c a l i z e d d e n s i t y of s t a t e s o f A - s i :H:x

C4-698 JOURNAL DE PHYSIQUE

F i g 5. shows t h e IR s p e c t r a of oxygenic f i l m s which a r e d e p o s i t e d a t 2200C, 330°C s u b s t r a t e t e m p e r a t u r e r e s p e c t i v i t y . I t g i v e s u s an evidence t o show t h a t t h e f i l m c o n t a i n s oxygen a t h i g h e r growing t e m p e r a t u r e more t h a n a t low temperature. And t h e 2000-2100 cm-I IR t r a n s m i s s i o n peaks of h i g h e r growing t e m p e r a t u r e f i l m a r e c o n s t r i c t e d , it p r e s e n t s t h a t t h e s i - H , s i - H 2 mode d e c r e a s e .

F I E m EFFECT MEASUWMENT: I n F i g 6. t h e l o c a l i z e d d e n s i t y of s t a t e s N(E) eve' of t h o s e f i l m s a r e given. Xvidently, t h e l o c a l i z e d d e n s i t y of s t a t e s of oxygenic A - s i f i l m compared w i t h t h e undoping f i l m h a s on change.

According t o t h e above r e s u l t s , we may make t h e f o l l o w i n g conjec- t u r e ; w i t h a h i g h e r t e m p a r e t u r e growing p r o c e s s t h e f i l m s c o n t a i n a s m a l l e r amount of hydrogen, t h e r f o r e , t h e b r i d g i n g oxygen may e a s i l y be formed i n t h e network; an a p p r o p r i a t amount q u a n t i t y of 0, o r N2/02 mixed g a s n o t o n l y d e c r e a s e t h e number of d e f e c t s and t h e r e b y i n c r e a s e t h e recombination l i f e t i m e , but a l s o i n c r e a s e t h e m o b i l i t y of c a r - r i e r s . The a d and aDh of A - s i : H f i l m s can be enhanced by a s m a l l q u a n t i t y of t h e s e g a s e s , t h e r e f o r e , t h i s phenomina may be r e l a t e d t o t h e v a r i a t i o n s observed i n some of e l e c t r i c p r o p e r t i e s of A - s i .

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J. Non-Cryst, S o l i d s 11 (1976) 219 3. C a r l s o n , D.E Wronski C.R.

Ap 1 Phys ~ e i t 28 (1976) 6'71

4. d g h t s . J.C, S t r e e t . R.A, Lucovsl:g. G J. ~ o n - C r - s t , s o l i d s . 35-36. (1980) 279.

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