INFLUENCE OF HYDROGEN PARTIAL PRESSURE ON DEPOSITION AND PROPERTIES OF SPUTTERED AMORPHOUS GALLIUM ARSENIDE

(1)

HAL Id: jpa-00220774

https://hal.archives-ouvertes.fr/jpa-00220774

Submitted on 1 Jan 1981

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

INFLUENCE OF HYDROGEN PARTIAL PRESSURE ON DEPOSITION AND PROPERTIES OF

SPUTTERED AMORPHOUS GALLIUM ARSENIDE

L. Alimoussa, H. Carchano, J. Thomas

To cite this version:

L. Alimoussa, H. Carchano, J. Thomas. INFLUENCE OF HYDROGEN PARTIAL PRESSURE ON DEPOSITION AND PROPERTIES OF SPUTTERED AMORPHOUS GALLIUM ARSENIDE.

Journal de Physique Colloques, 1981, 42 (C4), pp.C4-683-C4-686. �10.1051/jphyscol:19814151�. �jpa-

00220774�

(2)

J O U R N A L D E P H Y S I Q U E

Co

LZoqxe

,C4,

suppldmennt au nO1O, Toms

42,

ocl-obre

1 9 6 1

page

C4-683

INFLUENCE OF HYDROGEN PARTIAL PRESSURE ON DEPOSITION AND PROPERTIES OF S P U T T E R E D AMORPHOUS GALLIUM ARSENIDE

L . A l i m o u s s a , H. Carchano and J . P . ~ h o m a s *

Labom t o i r e de Photo6Zectricit6, Lquipe

ll,Vatdm*atcx

Amo~pl-ios", FacuZzr' des Scien,yes e t Technique3

d~

Saint-Jdro^rne,

23

rue

Pnincard, ³³⁶⁹⁷

!b!a~sei27e Ceriex

1.3,

l.%ance

* l n s t i t t c t de Physique Nu~Z&uir@, Nniversitg de Lgon

I , 4 6

bd du

11

novernbre

1 9 7 8 , $962;' V i

2 Zeurbanns Cedex, fiance

A b s t r a c t . - T h i n f i l m o f il % A s H a r c p r o d u c e d hy r f s p u t t s r i n ~ o f a mnriocrys-

-

- -

-

- - -

t , ) l l i n n ~ . ~ n d o p c d t a r g e t ( p 3. 5 x 107 Rxcml

.

^IJeh a v e correlated t h e h y d r o g e n p r e s s u r e PH o f t h e d i s c t ~ a ~ , g e w i t h t h e I I c ~ n c c n t r ~ ~ t i o n CH i n t n e S i l n +rum nuclear r n g c t i o n o f "N. S t u d y o? g r o w t h r a t e v a r i a t f o n w i t h P I ( shnws a d e c r e a - s c f r o m 3 A/S t o s l ~ o u t 1

K/s

when l l y ~ j r o g c n i s adderi t o argon.-a-CdA?,-H i n s t r o n g l y a l l s u r b e n t (0. > 105 cln-1 a t 2 R V ) . The o p t i c a l g a p Eo i n c r e d s e r , w i t h I'H f r o m 0.9'1 e V a n d s , a t u r , a t e s t o 1 . 4 5 nV when PI1 > 4 @ 4 o f t o t a l p r c s s u r e .

1.

I n t r o d u c t i o n .

-

An i n c r e a s e d i n t e r e s t h a s b e e n c a r r i e d t o amorphous s e m i c o n d u c t o r s when CHITTICK e t a l .

[

1

]

o b s e r v e d a g r e a t p h o t o c o n d u c t i v e e - f f e c t i n h y d r o g e n a t e d amorphaus s i l i c o n d e p o s i t e d by d g l o w d i s c h a r g e i n s i l a n e . They o b s e r v e d a l s o t h a t s m a l l a m o u n t s o f p h o s p h i n e i n t h e s i l a n e c o u l d s u b s t i t u t i o n a l l y d o p e t h e f i l m s . I t h a s a l s o b e e n shown t h a t f i l m s s p u t t e r e d i n a n a r e o n - h y d r o x e n a t m o s p h e r e e x h i b i t s i m i l a r p r o p e r t i e s

[

²

1.

^{A s}amorphous s i l i c o n d e p o s i t e d by e v a p o r a t i o n o r s p u t t e r i n g i n a p b r e - a r g o n a t m o s p h e r e h a s a p o o r p h o t o c o n d u c t i v i t y i t i s g e n e r a l l y a c c e p t e d t h a t t h e p r e s e n c e o f h y d r o g e n i n t h e s e m i c o n d u c t o r i s r e s p o n s i b l e f o r good p h o t o n l e c - t r i c a l p r o p e r t i e s . The h y d r o g e n c o m p e n s a t e s d a n e l i n g b o n d s ant1 t h u s d e n s i t y o f sts- t e s i n t h e g a p i s r e l a t i v e l y s m s l l

[

3

1 [

4

1 .

The a i m of t h i s p a p e r i s t o i n v e s t i - g a t e t h e s p e c t r a l d e p e n d e n c e o f t h e o p t i c a l c o n s t a n t s o f h y d r o g e n a t e d amorphous g a l - l i u m a r s e n i d e n e a r t h e a b s o r p t i o n e d g e w i t h h y d r o g e n c o n t e n t and t o c o r r e l a t e h y d r o - g e n c o n t e n t CH w i t h h y d r o g e n p a r t i a l p r e s s u r e pkl i n s p u t t e r i n g g a s . A l t h o u g h i t i s p o s s i b l e t o d e p o s i t s amorphous g a l l i u m a r s e n i d e by glow d i s c h a r g e i n a m i x t u r e o f t h r i m e t h y l g a l l i u m a n d a r s i n e , we h a v e c h o s e r t h e e a s i e r method o f sputter in^ i n a r g o n - h y d r o g e n a t m o s p h e r e . Moreover t h i s method, compared w i t h t h e glow t e c h n i q u e , p r e s e n t s t h e g r e a t a d v a n t a g e t o p e r m i t t h e c o n t r o l o f tiydroeen c o n t e n t El, o f t h e m a t e r i a l by t h e v a r i a t i o n o f p a r t i a l p r e s s u r e p l l a f t h e s p u t t e r i n g g a s m i x t u r e which makes p o s s i b l e a s y s t e m a t i c s t u d y o f t h e d e p e n d e n c e o f m a t e r i a l p r o p e r t i e s on h y d r o - g e n c o n c e n t r a t i o n .

2. Experimental procedure.

m o n o c r y s t a l l i n e w a f e r w i t h p r e s s u r e o f h y d r o g e n .

-

A.GaAs-H f i l m s w e r e d e p o s i t s d by r f s p u t t e r i n g o f a a p l a s m a made i n a r g o n a n < . v a r i a b l e b u t c o n t r o l l e d p a r t i a l -we h i v e u s e d two t y p e s o f s u b s t r a t e . O p t i c a l c h a r a c t e r i z a t i o n i s made o n p y r e x p r i s m s w i t h f a c e s s l o p e d t h r e e d e g r e e s t o a v o i d ~ n u l t i p l e r e f l e x i o n s . Hydrogen c o n c e n - t r a t i o n i s m e a s u r e d i n f i l m s d e p o s i t e d o n p o l i s h e d s t a i n l e s s - s t e e l s u b s t r a t e s .

F i l m a m o r p h i c i t y i s c h e c k e d by t r a n s m i s s i o n e l e c t r o n i c m i c r o s c o p y . D i f . f r a c t i o n s p e c t r u m a n a l y s i s shows t h a t t h e d e p o s i t r e m a i n s amorpholls, w h i l e s u b s t r a t e tempe- r a t u r e i s h e l d b e l c w 30°C d u r i n g t h e d e p o s i t . On t h e o t h e r hand, a l a y e r s u b m i t t e d t o a t h e r m a l a n n e a l i n g b e g i n s t o c r y s t a l l i z e a t a b o u t 3 5 0 ° C . To o b t a i n amorphous l a y e r s t h e s u b s t r a t e h o l d e r i s w a t e r c o o l e d d u r i n g t h e d e p o s i t .

3. Measurement o f hydrogen content.

-

The t o t a l h y d r o g e n c o n c e n t r a t i c n O F l a y e r s i s m e a s u r e d by n u c l e a r r e a c t i o n b e t w e e n ' 5 ~ a n d H a c c o r d i n g t o t h e r e a c t i o n

[

5

1

T h i s e x p e r i m e n t a l l o w s making a n h y d r o g e n c o n c e n t r g t i o n p r o f i l e a l o n g t h e t h i c k n e s s o f t h e l a y e r . The r e s o l u t i o n o f t h i s method i s 35 A.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19814151

(3)

C4-684 JOURNAL DE PHYSIQUE

R e s u l t s f o r d i f f e r e n t s a m p l e s a r e shown i n t a b l e 1 . The m e a s u r e m e n t s e v a l u a t e t h e r a t i o o f h y d r o g e n a n d g a l l i u m a t o m s . I f i t is assumed t h a t GaAs i s s t o e c h i o m e - t r i c , we o b t a i n t h e r a t i o of numbers o f h y d r o g e n a t o m s p r e s e n t i n t h e m a t e r i a l a n d m o l e c u l e s o f GaAs. L e t u s n o t e t h a t C must b e d i v i d e d by two i f i t i s c a l c u l a t e d i n r e l a t i o n t o t o t a l number o f a t o m s P i k e f o r h y d r o g e n a t e d s i l i c o n

1 2 3 4 1

I

( D e p o s i t i o n : pH=9x10:' t o r r : p H = 2 x ~ ~ - 3 t o r r : p = ~ . ~ x ~ ~ T ~ t o r r _H : p = a x ~ o - ~ t o r r _H 1

( c o n d i t i o n s : pT=9x10 3 t o r r : p = l o - ' t o r r : pT=1,4x10 ' t o r r : pT=?,Gx?O ' t o r r )

[ T

( C H m o l % 39 54 70 - 80 70 - 8 6 I

A v e r a g e : 77

:

A v e r a g e : 77 1

(-

-

^I

We c a n o b s e r v e t h a t h y d r o g e n c o n c e n t r a t i o n C i n c r e a s e s a t f i r s t w i t h p a r t i a l p r e s s u r e p b u t s a t u r a t e s a t a n a v e r a g e v a l u e o f a!out 77 % f o r p > 40 %. S e v e r a l measuremengs a t t h e same p o i n t o f a s a m p l e g i v e t h e same r e s u l t s . H

On t h e o t h e r hand, by making two m e a s u r e m e n t s a t two d i f f e r e n t s p o i n t s o f a s a m p l e , we h a v e r e c o r d e d two d i f f e r e n t p r o f i l e s o f h y d r o g e n c o n c e n t r a t i o n . T h i s r e - s u l t shows t h a t t h e h y d r o g e n b i n d i n g i n t h e m a t e r i a l i s n o t v e r y homogeneous b u t we c a n o b s e r v e a t f i g u r e 1 t h a t h y d r o g e n c o n c e n t r a t i o n i s r e l a t i v e l y c o n s t a n t a l o n g t h e f i l m t h i c k n e s s .

4.

Influence o f p O n

de o.Siti0n rate.

- The d e p o s i t i o n r a t e d e c r e a s e s when pH i n - c r e a s e s . We h a v e eeasure! by TOLANSKY method

[

6

]

t h e t h i c k n e s s s a m p l e s o b t a i n e d f o r d i f f e r e n t h y d r o g e n p r e s s u r e s . We o b s e r v e i n f i g u r e 2 t h a t t h e d e p o s i t i o n r a t e d e c r e a s e s r a p i d l y when p, c h a n g e s f r o m 0 % t o 20 %.

Above,20 % t h e d e c r e a s e i s s l o w e r and t h e d e p o s i t i o n r a t e i s g o i n g t o a l i m i t v a l u e o f 1 A / S . T h i s r e s u l t i s n o t s u r p r i s i n g s i n c e t h e p u l v e r i s a t i o n y i e l d d e p e n d s upon t h e mass o f i n c i d e n t i o n s . B u t t h e s l o p e o f t h e c u r v e s u g g e s t s t h a t t h e p r e s e n c e o f h y d r o g e n i n t h e p l a s m a c o n t r o l s t h e y i e l d more t h a n t h e q u a n t i t y o f h y d r o g e n . I n d e e d , a d d i n g h y d r o g e n r e d u c e s t h e i o n i s a t i o n p o t e n t i a l o f t h e p l a s m a s i n c e t h e h y d r o g e n i o n i s a t i o n p o t e n t i a l i s e q u a l t o 13.60 V w h i l e t h e a r g o n i o n i s a t i o n p o t e n t i a l i s e q u a l t o 15.76 V

[

7

1.

When a r g o n p r e s s u r e i s k e p t c o n s t a n t , t h e p r e s e n c e o f hy- d r o g e n r e d u c e s t h e number o f i o n i s e d a t o m s o f a r g o n , w h i c h a r e more e f f i c i e n t i n t h e p u l v e r i s a t i o n phenomenon, and t h u s t h e d e p o s i t i o n r a t e d e c r e a s e s . An i n c r e a s e of h y d r o g e n d o e s n o t g i v e a g r e a t v a r i a t i o n o f i o n i s e d a t o m s o f a r g o n a n d t h e d e - p o s i t i o n r a t e d o e s n o t c h a n g e v e r y much.

5.

Optical properties. -

^W^e h a v e m e a s u r e d t h e v a r i a t i o n s o f a b s o r p t i o n s p e c t r u m a ( h v 1 w i t h t h e h y d r o g e n p a r t i a l p r e s s u r e pH. From t h e s e c u r v e s we h a v e c a l c u l a t e d t n e v a r i a t i o n o f o p t i c a l g a p E w i t h pH.

To d e t e r m i n e o p t i c a l p r o p e r t i e s o f a GaAs-H w e h a v e u s e d a method a n d a n a p p a - r a t u s a c h i e v e d by E . PELLETIER e t a l .

[

8

]

f o r t h i n f i l m s .

With t h i s a p p a r a t u s i t i s p o s s i b l e t o m e a s u r e r e f l e c t i o n and t r a n s m i s s i o n d a t a f o r p h o t o n e n e r g i e s b e t w e e n 1 . 6 e v a n d 6 e v . Moreover, t h e amorphous g a l l i u m a r s e n i d e a b s o r b s t h e w h o l e i n c i d e n t e n e r g y a b o v e 2 . 7 6 e v a n d o u r d a t a a r e g i v e n f o r p h o t o n e n e r g i e s b e t w e e n 1 . 6 e v a n d 2.76 e v . From R. R ' a n d T a n c o m p u t i n g program g i v e s t h e f i l m t h i c k n e s s , t h e v a l u e s of e x t i n c t i o n c o e f f i c i e n t k and r e f r a c t i v e i n - d e x n a s f u n c t i o n s o f p h o t o n e n e r g y hv. V a l u e s o f a b s o r p t i o n c o e f f i c i e n t a a r e c a l - c u l a t e d f r o m k ( h v ) d a t a . A s f o r a-Si-H, t h e o p t i c a l band g a p E i s d e t e r m i n e d by p l o t t i n g ( a h v ~ ' / ~ a s a f u n c t i o n o f h u . I n d e e d t h e b e h a v i o r o f t g i s f u n c t i o n i s p r e d i c - t e d f o r amorphous s e m i c o n d u c t o r s i f t h e band e d g e s a r e p a r a b o l i c

[

9

1.

F i g u r e 2 p r e s e n t s t h e r e f r a c t i v e i n d e x n a s a f u n c t i o n o f p h o t o n e n e r g y hV f o r d i f f e r e n t h y d r o g e n a t e d s a m p l e s .

We c a n o b s e r v e t h a t n r e a c h e s a maximum b e t w e e n 2 e v a n d 2 . 1 7 e v . T h i s v a l u e i n c r e a s e s w i t h pH and a b o v e a b o u t p = 20 % d e c r e a s e s a n d r e a c h e s t h e u n h y d r o g e n a - t e d v a l u e f o r pH > 4 0 %. ^H

(4)

F i g u r e 3 shows t h e s h i f t o f t h e a b s o r p t i o n edge as pl, i s v a r i e d . We c a n o b s e r - v e t h a t t h e edge s h i f t s t o l a r g e r p h o t o n e n e r g i e s when hydrogen i s added t o argon.

I t i s r e m a r k a b l e t h a t p l o t s a r e r o u g h l y t h e same f o r any hydrogen p r e s s u r e pH. F o r comparison we have p l o t t e d cx v a r i a t i o n s f o r c r y s t a l l i n e s i l i c o n and crystalline g a l l i u m a r s e n i d e 1 1 0

1

f o r hydrogenated amorphous s i l i c o n

[

1 1

]

and f o r hydrogena- t e d arrorphous g a l l i u m a r s e n i d e o f W. PAUL e t a l . [ I 2

1.

^{I t}can be n o t e d t h a t a t 2.5 ev, w h i c h i s t h e p h o t o n e n e r g y where t h e s o l a r s p e c t r u m i s maximum, t h e a-GaAs-H a b s o r p t i o n i s 25 t i m e s t h a t o f c . S i and t w i c e t h a t o f a - S i - H . The o p t i c a l gap c a l c u l a t e d b y p l o t t i n g - (ahv1112 a s a f u n c t i o n o f hv a r e p l o t t e d i n f i k u r e 1 Wo can' o b s e r k t h a t Eo'increase's v e r y r a r ~ i d l y when PI+ v a r i e s f r o m 0 % t o 20 %. P.!:ove 20 % Eo i n c r e a s e s v e r y s l o ~ d l y and r e a c h e s a c o n s t a n t v a l u e f o r PH > 40 %, where CH r e m a i n s c o n s t a n t w i t h i n c r e a s i n g Pt1 ( t a b l e I ) .

6 . C O ~ C ~ U S ~ O ~

. -

The d g p o s i t i o n r a t e As a f u n c t i o n o f h y d r o g e n p a r t i a l p r e s s u r e pH. I t d e c r e a s e s f r o m 3 A/S t o a b o u t 1 A/S when pH i n c r e a s e s f r o m 0 % t o 40 %. I t i s supposed t h a t t h e a d d i n g o f hycrogen r e d u c e s t h e number o f i o n i s e d a r g o n atoms w h i c h a r e t h e more e f f e c t i v e i o n s i n t h e d i s c h a r g e . The t r a n s m i s s i o n d a t a o f a GaAs-H p r e - p a r e d u n d e r d i f f e r e n t hydrogen p a r t i a l p r e s s u r e s pH y i e l d i n f o r m a t i o n a b o u t t h e dependence o f r e f r a c t i v e i n d e x and a b s o r p t i o n edge. The v a r i a t i o n o f r e f r a c t i v e i n - d i c e s o f b o t h u n h y d m g e n a t e d and h y d r o g e n a t e d f i l m s i s t h e same and p r e s e n t s a m a x i - mum between 4.2 and 4.37 f o r p h o t o n e n e r g i e s between 2 ev and 2.17 ev. Around i t s maximum v a l u e n v a r i e s r a p i d l y . The a b s o r p t i o n edge, and t h e r e f o r e t h e o p t i c a l gap, , s h i f t s t o h i g h e r e n e r g i e s a s t h e h y d r o g e n c o n t e n t i s i n c r e a s e d . When h y d r o g e n i s

f i r s t added t h e s h i f t i s v e r y r a p i d f r o m 1.05 ev t o 1.4 ev. I t can be presumed t h a t h y d m g e n e l i m i n a t e s s t a t e s i n t h e gap t h r o u g h compensation o f d a n g l i n g bonds.

T h e r e a f t e r t h e s h i f t i s s l o w e r and o p t i c a l gap E r e a c h e s a c o n s t a n t v a l u e w h i c h i s a b o u t 1.45 ev. These r e s u l t s c o n f i r m t h e m e a s u r e i e n t s o f hydrogen c o n t e n t made by n u c l e a r r e a c t i o n . Indeed, hydrogen c o n t e n t CH i n c r e a s e s f o r p v a r i a t i o n s f r o m 0 % t o 40 %. F o r p ) 40 % h y d m g e n c o n t e n t CH remains e q u a l t o 7y % m o l .

I t can be note! t h j t a-GaAs-H has a gap l o w e r o r s l i g h t l y g r e a t e r t h a n t h e C.GaAs gap w h i c h i s o f 1.4 ev, w h i l e a - S i - H has a l w a y s a gap g r e a t e r t h a n C.Si.

ACKNOWLEDGMENTS. - We w i s h t o e x p r e s s o u r g r a t i t u d e t o Dr E . PELLETIER and

M. LAZARIDES f o r v a l u a b l e a s s i s t a n c e and h e l p f u l d i s c u s s i o n s on o p t i c a l c h a r a c t e r i - z a t i o n . T h i s work was s u p p o r t e d b y Commissariat B 1 ' E n e r g i e S o l a i r e (COMES) and E l e c t r i c i t 6 de F r a n c e (E.0.F.).

REFERENCES

[

¹

]

^R.C. ^CHITTICK ^;^J.H. ^ALEXANDER ^:M.F. STERLING : J . E l e c t r o c h e m . Soc.

116

(19691 77

r

²

¹

^W. ^PAUL^:^A.J. LEWIS : G.A.N. CONNEL : J.P. MOUSTAKAS : S o l i d S t a t e Commun.

-

²

20 (19761 989

h

3

1 ^KG.

^LECOMBER ^;^{A. MADAM}^;^W.E. SPEAR : J. Non C r y s t . S o l i d s (1972) 219

1-

⁴

1

H. FRITZSCHE I C.C. TSAI ; P. PERSANS : S o l i d S t a t e Technol. 21 (19781 5 5

1 1

5 ] ^J.P. ^THOMAS ^;C. PIJOLAT ; M. FALLAVIER : Rev. Phys. A p p l . 1 3 7 1 9 7 8 1 433 [ - 6 ] - S. TOLANSKY : " S u r f a c e M i c r o t o p o g r a p h y " I n t e r s c i e n c e P u b l i s h e r s , London

(19601

1 7

]

^L.B. ^LOEB ^:" B a s i c P r o c e s s e s o f gaseous e l e c t r o n i c s " U n i v e r s i t y o f C a l i f o r n i a P r e s s (1961 1 p. 698 and p. 989

[

⁸ E. PELLETIER : P. ROCHE ; B. VIDAL : NOUV. Rev. O p t i q u e

1

(19761 353 [ 9 E.A. DAVIS : "Amorphous S e m i c o n d u c t o r s " ed b y P.G. L e Gomber, J . M o r t .

Academic P r e s s - New York (19731

[ l o ]

J . J . LOFERSKI : "The p r i n c i p l e s o f P h o t o v o l t a i c S o l a r Energy C o n v e r s i o n "

Brown U n i v e r s i t y - Rhode I s l a n d ( 1 9 7 2 )

[

1 1

]

O.E. CARLSON ; C.R. WRONSKI : "Amorphous Semiconductors" E d i t o r M.M. Brodsky . S p r i n g e r V e r l a g (19791 p. 294

[

1 2

]

^W. PAUL ; T.D. MOUSTAKAS : O.A. ANDERSON : E. FREEMAN : 7th I n t . Conf. o n L i q u i d and Amorphous Semiconductors. Ed. b y W.E. S p i c e r (19771 p. 467.

(5)

C 4 - 6 8 6 J O U R N A L DE PHYSIQUE

F i g u r e 1

F i g u r e 2

.I.S E&"(c3

%

1. 0

>

0

(I

9

W

1 I I A A

" h b

^,:

F i g u r e 3

&. 20 S0.s

40

HYDRCXEN PARTIAL P R E S W E PdF)%

P $ 2 ' -

i 8

1

F i g u r e 4

-',

^,/*

- :<

(',

\

-

\

-

:

^\^\\^\

^- ^-

--\-