LIQUID PHASE EPITAXIAL GROWTH OF InxGa1-xAs/ InP NEAR SOLID INSTABILITY

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LIQUID PHASE EPITAXIAL GROWTH OF InxGa1-xAs/ InP NEAR SOLID INSTABILITY

M. Joncour, J. Benchimol, J. Burgeat, M. Quillec

To cite this version:

M. Joncour, J. Benchimol, J. Burgeat, M. Quillec. LIQUID PHASE EPITAXIAL GROWTH OF

InxGa1-xAs/ InP NEAR SOLID INSTABILITY. Journal de Physique Colloques, 1982, 43 (C5), pp.C5-

3-C5-10. �10.1051/jphyscol:1982501�. �jpa-00222220�

CoZZoque C5, supplirnent au n012, Tome 43, de'cernbre 1982 page C5-3

L I Q U I D

PHASE EPITAXIAL GROWTH OF 1n,~a, -,AS/I~P NEAR SOLID INSTABILITY

M.C. Joncour, J.L. Benchimol, J. Burgeat and M. Q u i l l e c

Centre NationaZ dlEtudes des Te'Ze'comunications, PAB/PMS/SPD, 196 m e de Paris, 92220 Bagneux, France

.Resume.

-

On e t u d i e l ' i n f l u e n c e du s u b s t r a t InP s u r l a croissance

a

p a r t i r de l a p h a s e l i q u i d e de couches de t e r n a i r e InxGal-xAs. Les r e s u l t a t s experimentaux m e t t e n t en evidence c e t t e i n f l u e n c e t a n t pour l a croissance s u r des s u b s t r a t s d ' o r i e n t a t i o n

(001) que (111)B. L 1 i n t e r p r @ t a t i o n e s t f a i t e ii l ' a i d e du modele des s o l u t i o n s simples en prenant en compte l ' e n e r g i e e l a s t i q u e due ii l a presence du s u b s t r a t . Cependant, s i ce modele assure une bonne d e s c r i p t i o n de l a croissance epi t a x i a l e s u r un s u b s t r a t (OOl), une p r i s e en compte de l a c i n e t i q u e semble necessaire pour d e c r i r e l a c r o i s - sance sur un s u b s t r a t (111).

Abstract.

-

The i n f l u e n c e o f the InP s u b s t r a t on InxGal-XAs l i q u i d phase e p i t a x i a l l a y e r s i n t h e v i c i n i t y o f t h e c r i t i c a l temperature i s analysed. T h i s i n f l u e n c e i s c l e a r l y proved f o r b o t h (001) and (111)B growth o r i e n t a t i o n , and i n t e r p r e t e d by means o f the simple s o l u t i o n model, t a k i n g i n t o account t h e s t r a i n energy induced by the substrate. A1 though t h i s model g i v e s a good d e s c r i p t i o n o f e p i t a x i a l growth on (001) substrates, i t seems necessary t o i n c l u d e growth dynamics i n (111) growth d e s c r i p t i o n .

1. I n t r o d u c t i o n . - S o l i d s o l u t i o n s InxGal-xAsl- Py have become o f considerable i n t e r e s t f o r f a b r i c a t i n g 1.R l a s e r diodes f o r o p t i c a l tglecommunications. Most o f t e n , these devices are prepared v i a 1 iq u i d phase e p i taxy (LPE), s e l e c t i n g compositions

r ,

y t h a t r e s u l t i n InP l a t t i c e matched e p i l a y e r s . The InxGal-xAs a l l o y can be grown l a t t i c e matched t o InP s u b s t r a t e f o r x = 0.53. R e f e r i n g t o B u b l i k and L e i k i n c a l c u l a - t i o n s C

17,

the c r i t i c a l temperature o f I n 0 50Gao 5oAs a l l o y i s 600°C.

This i s q u i t e c o n s i s t e n t w i t h the value taken fr6m r e f .2 i n which de Cremoux e t a l C 4 c a l c u l a t e d the spinodal isotherms f o r t h e InxGal-xAsl- Py a l l o y . The commonly used LPE growth temperature range (600

-

650°C) i s thus q u i f e c l o s e t o the c r i t i c a l value.

We b e l i e v e t h a t the v i c i n i t y o f i n s t a b i l i t y leads t o s t r o n g " l a t c h i n g - e f f e c t " . Such an e f f e c t has been observed by S t r i n g f e l l o w r 3 J on GaxInl_,P l a y e r s . He found t h a t v a r i a t i o n s i n t h e l i q u i d s o l u t i o n composition induces much l e s s v a r i a t i o n i n the s o l i d than p r e d i c t e d by a r e g u l a r s o l u t i o n model

.

He a t t r i b u t e d t h i s discrepancy t o the e l a s t i c s t r a i n induced by the s u b s t r a t e . To i n c l u d e q u a n t i t a t i v e l y t h e l a t t i c e mismatch s t r a i n energy i n the phase diagram c a l c u l a t i o n , Nahory and a1 C4J, using Jesser and Kuhlmann-Wi l s d o r f [5] c a l c u l a t i o n s , proposed the f o l l o w i n g expression :

b G ~ t r a i n = a-a

0 2 (-B-

1 +v ⁰

w i t h o = 2 c G VM

where C ( = 1/2 c 4) i s the i n t e r f a c i a l shear modulus o f the l a y e r , v i s t h e Poisson r a t i o and V i t 2 molar volume.

This term w h c h vanishes f o r a = a0 ( l a t t i c e matched growth) i s the main f a c t o r con- t r o l 1 i ng the composition nearby t h e c r i t i c a l temperature (Tc)

.

Indeed, near Tc the m i x i n g energy v a r i e s s l o w l y w i t h composition, so t h a t e q u i l i b r i u m can be s t r o n g l y influenced by t h e above energy term. Even a t temperatures lower than Tc can the s o l i d s o l u t i o n be s t a b l e thanks t o t h i s s t r a i n energy term as was shown i n t h e InxGal-8Asl-yPy system [6J. A sharp minimum i n the AG versus composition curve i s then b u i l t around l a t t i c e matching, l e a d i n g t o ltpul l i 3 - e f f e c t " The purpose o f t h i s paper i s t o study p o s s i b l e " p u l l i n g - e f f e c t " i n InxGal-xAs a l l o y t 71. S l i g h t l y mis-

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982501

C5-4 JOURNAL DE PHYSIQUE

matched layers were grown a t various temperatures on InP (001) and (111)B. We present experimental liquidus and solidus data and compare these r e s u l t s with the simple solution model calculation.

2.Experimental procedure.- The InxGal-xAs c r y s t a l s studied i n t h i s work were grown by conventionnal LPE, using a semi-transparent furnace. Three s e r i e s of approximati -

vely 10 layers each were perfomed

;

the gallium concentration i n the liquid was kept constant i n each s e r i e s

:

- Growth on InP(001) substrajie

1) Around 650°C x Ga

=

0.025

x a ~ ~

=

0.057 t o 0.065.

2) Around 550°C x'~a

=

0.015

x ' ~ ~

⁼

0.015 t o 0.024 3 ) Growth on InP (111)B substrate

Around 650°C

X ' G ~ =

0.0282

X'AS =

0.054 t o 0.065

After a d i r e c t measurement of the liquidus temperatures (within

?

1°C), the growths were carried by super-cool ing technique. The supersaturation step was 2.3OC and the films were grown to a thickness of 3 t o

5

um. The samples were then characterized both by X-ray d i f f r a c t i o n and electron microprobe analysis.

On the other hand, some non-epitaxial p l a t e l e t s were grown f a r from lattice-matching.

Their composition were measured by m i croprobe analysis on1 y a f t e r removing t h e InP substrate w i t h HC1 a s a s e l e c t i v e etchant.

The X-Ray rocking curves were used both t o determine the perpendicular and parallel l a t t i c e parameters (and therefore the layers composition) and t o check the c r y s t a l - 1 ine q u a l i t y of the samples. The rocking curves were measured by means of (n,-n) parallel s e t t i n g of the X-Ray double crystal arrangement, using CuKu radiation.

Before epitaxy, the q u a l i t y of the InP substrates was checked using the double d i f f r a c t i o n p r o f i l e s . The rocking curve parameters a r e

:

the f u l l width a t half maximum (FWHM) 12.5 sec of arc, and the maximum double r e f l e c t i o n c o e f f i c i e n t ( r e f l e c t i v i t y ) 0.38. Thoses values a r e i n good agreement w i t h the predictions of the dynamical d i f f r a c t i o n theory [8], which gives, f o r an InP perfect c r y s t a l , respecti- vely 9.09 sec of a r c and 0.46 f o r FWHM and r e f l e c t i v i t y . This s l i g h t discrepancy between theory and experiment can be a t t r i b u t e d t o defects present i n InP bulk c r y s t a l s 19J.

The perpendicular r e l a t i v e mismatch ( ~ a / a ) & w a s measured using the InP 004 CuKa symmetric Bragg r e f l e c t i o n f o r InP(001) oriented substrates, and InP 333 CuKu r e f l e c t i o n f o r InP ( I 1 l ) B substrates .The parallel r e l a t i v e mismatch (Aa/a)" was deduced from InP (115) CuKa asymnetrical reflections using

:

and

L a L - g M )

A a =

~i naCOSa

(-

a a

where a i s the angle between hkl plane and the surface of the layer.

3.Experimental r e s u l t s and discussion - Results of X-Ray measurements on InP(001)

substrates a r e shown i n figure I. Tetragonal d i s t o r t i o n c l e a r l y occurs, ( ~ a / a ) " i s

nearly nu1 1 f o r the e p i t a x i a l samples. The approximation of e n t i r e l y e l a s t i c a l l y

s t r a i n e d layers i s thus j u s t i f i e d .

i . 1 : ( n a l a ) (3) and (aa/a)

'' (3)

va ues f o r growth on InP (001) around 550°C.

InP (100)

~k.10~ at-'

The l a y e r s composition i s then deduced, using t h e Hornstra c o r r e c t i o n c o e f f i c i e n t [ l d t h a t i s :

Aa s t r a i n f r e e Aa A

= K

(,I

The values o f l a t t i c e parameters and e l a s t i c s constants used r e s p e c t i v e l y i n Vegard's lawC131 and Hornstra c o e f f i c i e n t a r e g i v e n i n Table I:

Table I : Parameters used i n flnAs calculation C14J

t

C

L a t t i c e constants InP = 5.8687 GaAs = 5.6532 InAs = 6.0584

A

Hornstra c o e f f i c i e n t

C1l C11+2/3C

(100) K = (111) K =

c.

C1 1+2C12

ii+2C12

= 0.47 = 0.65

w i t h C = 2C44

-

^Cll

+

C12

E l a s t i c constants ( L i n e a r combination o f InAs and GaAs data).

2 12

1.016 1012 dyneslcm C12 = 0.509 10 dyneslcm 2 C1l =

C44 = 0.482 10 12 dynes/cm 2

On the b a s i s of our l i q u i d u s and s o l i d u s data near t h e In-Rich corner phase diagram, we have c a r r i e d o u t a semi-empirical c a l c u l a t i o n based on the simple s o l u t i o n model developed b y Panish and I 1 legems L15J. I n t h i s c a l c u l a t i o n , i n t e r a c t i o n parameters

s L

~ I ~ A S - G ~ A S i n t h e s o l i d and aIn-Ga i n t h e l i q u i d are considered as f i t t i n g parameters The f i t haS t o be o b t a i n e d f o r l a y e r s l a t t i c e matched a t growth temperature: So?

t a k i n g i n t o account t h e d i l a t a t i o n c o e f f i c i e n t s aInP and aInGaAs, l a t t i c e matching a t growth temperature leads t o t h e f o l l o w i n g mismatch a t room temperature:

C5-6 JOURNAL DE PHYSIQUE

na s t r a i n free

AT [aInP

-

^aInGaAs]

- ^-

a room temp. 1

-

aInp AT

where AT i s t h e d i f f e r e n c e between growth temperature and room temperature.

s t r a i n f r e e

That i s ($-) =

-

6 . 1 0 - ~ f o r growth a t 650°C room temp

=

-

4.5

l o m 4

f o r growth a t 550°C

Hence, assuming a p u r e l y e l a s t i c a l l y s t r a i n e d l a y e r , and then a p p l y i n g Hornstra's c o r r e c t i o n c o e f f i c i e n t , the perpendicular l a t t i c e mismatch a t room temperature would be =-

-

1,2 and

-

^9,5 f o r growth on (001j substrate, and 9,3 f o r growth on (111)B s u b s t r a t e . The values o f t h e parameters used i n the c a l c u l a t i o n a r e l i s t e d

i n t a b l e I 1

Table I 1 : Parameters f o r the l i q u i d - p h a s e diagram calculation,

-

5.7 i 10 K - l c1$

= 4.75 1 0 K 1 alnGaAs

-

GaAs = 1 5 1 1 K f u s i o n

InAs = 1215 K

GaAs = 16.64 c a l mole-' K-' AS f u s i o n

InAs = 14.52 c a l mole-' K-' I n t e r a c t i o n parameters

a G s = 9.16 T

+

5160 c a l mole-'

la&-

^{.I =}

^-

¹⁰

^{.T +}

3860 c a l mole-'

c a l mole-'

' '

(111)B 2000 i 100

The c o e f f i c i e n t u i n v o l v e d i n t h e s t r a i n energy term i s c a l c u l a t e d w i t h InP e l a s t i c constants from r e f . 13 f o r (001) growth o r i e n t a t i o n , and a f t e r performing tensor t r a n s f o r m a t i o n [18J f o r (111)B growth o r i e n t a t i o n , t h a t i s :

u(OOl) = 6.9 10 c a l mole" 5 u(lll) = 1.1 10 c a l mole 6

-

1

The values o f xInAs 5 f o r the t h r e e s e r i e s o f growth are p i o t t e d a g a i n s t t h e l i q u i d composition xAS i n f i g u r e s 11-a,b, L and c. The comparison between experimental and c a l c u l a t e d l i q u i d u s temperatures are given i n t a b l e 111.

perimental and calculated soli'dus data.

- simple solution model

- - - Takina e l a s t i c strain enew gy into account

X

:

from XRay measurement

? I-

Microprobe analysis -a- growth on I n P (001) T

=

550°C

InP (100)

a1

o aa

a02 003

acu

0.05

am

0.68 r

0.64 -

-b-

growth on InP (001) T

=

650°C

0.60 -

-c- growth on InP (111)B

T =

650°C

C5-8 JOURNAL DE PHYSIQUE

Table

I 1 1 :

Comparison between experimental and calculated liquidus

temperatures.

p l e s o l u t i o n model. I n s i d e t h i s zone, the f i t i s good, p r o v i d i n g the s t r a i n energy induced by the s u b s t r a t e i s taken i n t o account.

I n s p i t e of t h i s good agreement between theory and experiment, o e can n o t e from Table 11, the d i f f e r e n c e s between t h e values o f t3inAs-GaAs used i n t h e

and a ~ n - ~ a

c a l c u l a t i o n from growth on (001) and (111)B substrates. This d i f f e r e n c e , p o i n t e d o u t by various authors 1 1 9 3

,

may l e a d t o t h e f o l l o w i n g comments :

i- t h e simple s o l u t i o n model, which i s an e q u i l i b r i u m model, i s n o t a b l e t o describe e n t i re1 y e p i t a x i a1 growth.

ii- t h e model may g i v e a good i n t e r p r e t a t i o n o n l y f o r one o f t h e two growth o r i e n t a t i o n s .

Actual ly, we b e l i e v e t h a t growth on InP(001) i s w e l l described by t h i s model. As a m a t t e r of fact, comparison between phase diagram data from 1 i t e r a t u r e ( f i g u r e 111).

shows t h a t , whereas s i m i l a r r e s u l t s are obtained by t h e d i f f e r e n t authors on (001) o r i e n t a t i o n , the (111)8 o r i e n t a t i o n leads t o v e r y d i s s i m i l a r ones.

Fig.3

: Comparison o f various experimental data. Ref. 21 : Present work and M. Q u i l l e c and J.L.,Benchimol ( p r i v a t e communica- t i o n ) .

Note from r e f 20 and 21 t h a t (001) and (111) o r i e n t a t i o n s a r e d i F f e r e n t o n l y below 100°C.

Moreover, (001) o r i e n t a t i o n growth was proved t o be l i m i t e d by d i f f u s i o n i n t h e l i q u i d phase, which i s n o t t h e case on (111)B o r i e n t a t i o n . This i s c o n s i s t e n t w i t h t h e assumption o f e q u i l i b r i um a t the i n t e r f a c e i n t h e case o f growth on (001) o r i e n t a t i o n .

4- Concl usion- We have shown t h a t " p u l l i n g - e f f e c t " occurs i n LPE InxGal-xAs 1 ayers

.

This e f f e c t i s l i k e l y t o be r e l a t e d t o t h e v i c i n i t y o f the c r i t i c a l temperature. I n t h a t low s t a b i l i t y region, t h e substrate e f f e c t i s indeed the main f a c t o r c o n t r o l l i n g s o l i d composition.

The simple s o l u t i o n model, i n c l u d i n g t h e s t r a i n energy induced by the s u b s t r a t e gives a good i n t e r p r e t a t i o n o f t h i s phenomenon f o r (001) growth o r i e n t a t i o n . Nevertheless, i t seems necessary t o take growth k i n e t i c s i n t o account t o describe (111)B

e p i t a x i a1 growth.

Acknowled ment

-

The authors would l i k e t o thank C. DAGUET f o r e l e c t r o n microprobe

d.

LAIJNOlS f o r h e l p f u l discussions throughout t h i s wort.

JOURNAL DE PHYSIQUE

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