GROWTH AND CHARACTERIZATION OF GaxIn1-xAsyP1-y/InP QUANTUM WELLS

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GROWTH AND CHARACTERIZATION OF GaxIn1-xAsyP1-y/InP QUANTUM WELLS

C. Starck, L. Goldstein, M. Boulou, D. Bonnevie, M. Lambert, C. Audry

To cite this version:

C. Starck, L. Goldstein, M. Boulou, D. Bonnevie, M. Lambert, et al.. GROWTH AND CHAR- ACTERIZATION OF GaxIn1-xAsyP1-y/InP QUANTUM WELLS. Journal de Physique Colloques, 1987, 48 (C5), pp.C5-175-C5-178. �10.1051/jphyscol:1987534�. �jpa-00226738�

JOURNAL DE PHYSIQUE

Colloque C5, supplgment au noll, Tome 48, novembre 1987

GROWTH AND CHARACTERIZATION OF G~,I~,-,As,P,-~/I~P QUANTUM WELLS

C. STARCK, L. GOLDSTEIN, M. BOULOU, D. BONNEVIE, M. LAMBERT and C. AUDRY

Laboratoires d e Marcoussis, CR-CGE, Route de Nozay, F-91460 Marcoussis, France

Dans c e t a r t i c l e nous pr6sentons l e s r k s u l t a t s d e croissance e t c a r a c t 6 r i s a t i o n d e s t r u c t u r e s 5 puits quantiques GaInAsllnP e t GaInAsPlInP. Les couches s o n t prepar&es p a r Cpitaxie par jets molkculaires h sources gazeuses.

C o m m e Ie d 6 m o n t r e I'analyse d e s s p e c t r e s d e photoluminescence 5 basse tempCrature, l e s puits pr6sentent d e s i n t e r f a c e s t r g s abruptes. Nous interprktons l a s t r u c t u r e d e s s p e c t r e s par d e s fluctuations d ' i p a i s s e u r des puits d'une monocouche.

Abstract

We r e p o r t on t h e growth and c h a r a c t e r i z a t i o n of GaInAs/InP a n d GaInAsP/InP quantum wells structures. T h e e p i t a x i a l layers w e r e prepared by g a s source molecular b e a m e p i t a x y (GSMBE). As r e v e a l e d by low t e m p e r a t u r e photoluminescence, t h e wells e x h i b i t s h a r p interface?. We i n t e r p r e t e t h e PL s t r u c t u r e s a s o n e monolayer size fluctuations of t h e well thickness.

Introduction

R e c e n t l y i t h a s been shown t h a t g a s source molecular b e a m e p i t a x y (GSMBE) is of particular i n t e r e s t f o r t h e growth of InP and GaInAsP m a t e r i a l [I], [ Z ] . This technique allows t h e growth of h e t e r o s t r u c t u r e s with very sharp i n t e r f a c e s a s d e m o n s t r a t e d by t h e luminescence properties of single quantum wells or superlattice.

Growth conditions

Epitaxial l a y e r s of InP a n d GaInAsP a r e prepared by using AsH3 a s sources f o r t h e V elements. These g a s e s a r e introduced i n t o t h e growth c h a m b e r through a boron nitride cracking c e l l h e a t e d a t 1000°C. Conventional effusion c e l l s a r e used a s G a a n d In sources.

GaxInl-xAsyP1-y alloys lattice-matched t o InP ( ~ a / a < 10-3) c a n b e reproducibly grown in t h e whole composition r a n g e (0 < y < 1) with a low residual c a r r i e r c o n c e n t r a t i o n (n < 3 x 1015cm-3). The layers exhibit a good homogeneity over 2" d i a m e t e r s u b s t r a t e a s well f o r thickness (At/t < 10-2) a s f o r composition (Aafa < 10-3, 5kp/Ap < 10-3). The composition of t h e l a y e r s is controlled by photoluminescence a n d X-ray double diffractornetry.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987534

J O U R N A L D E PHYSIQUE

In o r d e r t o a c h i e v e high q u a l i t y a n d s h a r p i n t e r f a c e s b e t w e e n GaInAsP a n d InP, t h e t i m e n e e d e d t o e s t a b l i s h s t a b l e f l u x e s c o r r e s p o n d i n g t o a given solid c o m p o s i t i o n h a s t o b e a s s h o r t a s possible. With o u r e x p e r i m e n t a l s e t u p , t h i s t i m e d u r i n g which t h e growth is i n t e r r u p t e d is a f e w s e c o n d s (2 t o 5 s).

Using t h e s e conditions, s i n g l e q u a n t u m w e l l s w i t h d i f f e r e n t t h i c k n e s s e s a r e grown o n (100) I n P s e m i - i n s u l a t i n g s u b s t r a t e . In o r d e r t o m a k e m o r e e a s y t h e a n a l y s i s of t h e l u m i n e s c e n c e as a f u n c t i o n of t h e well thickness, m u l t i l a y e r u n d o p e d s t r u c t u r e s c o n s i s t i n g of a 3 0 0 n m t h i c k I n P b u f f e r l a y e r , a 5 0 0 n m t h i c k t e r n a r y o r q u a t e r n a r y c o n t r o l l a y e r plus Gao.47Ino.53As o r Gao.25Ino.55Po.45 q u a n t u m w e l l s w i t h d e c r e a s i n g t h i c k n e s s (Lz = 9, 4.5, 2.4 a n d 1.2 n m ) s e p a r a t e d by

1 5 0 n m I n P b a r r i e r s , a r e grown.

P h o t o l u m i n e s c e n c e a n a l y s i s

Low t e m p e r a t u r e (T = 6 K) p h o t o l u m i n e s c e n c e m e a s u r e m e n t s a r e p e r f o r m e d o n t h e m u l t i l a y e r s t r u c t u r e s b y using t h e 4 8 8 nm l i n e of a n A r laser.

P h o t o l u m i n e s c e n c e e x c i t a t i o n a n d c o l l e c t i o n f r o m t h e e p i t a x i a l s i d e of t h e s a m p l e a l l o w t o o b s e r v e l u m i n e s c e n c e of e a c h well w i t h o u t a n y a b s o r p t i o n f r o m t h e u p p e r wells. T h e p h o t o l u m i n e s c e n c e s p e c t r a a r e a n a l y s e d using a 640 m m f o c a l l e n g t h s p e c t r o m e t e r ( r e s o l u t i o n 0.3 nrn) a n d a c o o l e d G e d e t e c t o r .

A t y p i c a l s p e c t r u m of GaInAsJInP m u l t i l a y e r s t r u c t u r e with f o u r QW is shown o n f i g u r e I. For t h i s s p e c t r u m t h e pumping power is I W/cm2. No m o d i f i c a t i o n of t h e l i n e s h a p e i s o b s e r v e d w h e n t h e power is v a r i e d b e t w e e n 0.05 a n d 5 W cm-2. O n e c a n n o t i c e o n f i g u r e 1 t h a t when t h e well t h i c k n e s s is r e d u c e d t o l e s s t h a n 5 n m t h e well emission s p e c t r u m i s c h a r a c t e r i z e d by at l e a s t t w o peaks.

We a t t r i b u t e f o r e a c h w e l l t h e h i g h e s t e n e r g y p e a k t o a t r a n s i t i o n b e t w e e n t h e l o w e s t e i g e n s t a t e s of a n e l e c t r o n a n d a h e a v y hole. T h e s h i f t of t h e high e n e r g y p e a k a s a f u n c t i o n of t h e well t h i c k n e s s (Lz) i s r e p o r t e d o n f i g u r e 2 a n d c o m p a r e d t o t h e o r e t i c a l v a l u e s c a l c u l a t e d f o r a s q u a r e p o t e n t i a l well a s s u m i n g p a r a b o l i c d i s p e r s i o n relations f o r e l e c t r o n s a n d h o l e s a n d t h e following m a t e r i a l p a r a m e t e r s : GaInAs, Eg = 0.812 eV, m h h = 0.5 mo, m e = 0.041 m o ; InP, Eg =, 1.425 eV, m h h = 0.56 mo, m e = 0.08 mo. T h e c a l c u l a t i o n s h a v e b e e n c a r r i e d o u t f o r t w o r a t i o s of c o n d u c t i o n b a n d e - e d g e d i f f e r e n c e t o v a l e n c e b a n d - e d g e d i f f e r e n c e AEc/AEv 80120 a n d 20/80.

In f i g u r e 3 w e c o m p a r e t h e v a r i a t i o n of t h e linewidth of t h e high e n e r g y p e a k versus t h e well t h i c k n e s s t o t h o s e of GaInAsIInP QW grown e i t h e r by GSMBE o r by o t h e r t e c h n i q u e s [31. In o u r c a s e , when t h e p e a k i s n o t e n t i r e l y resolved, w e u s e a d e c o n v o l u t i o n t e c h n i q u e f o r l i n e w i d t h e s t i m a t i o n . O n e c a n n o t i c e , if o n e e x c e p t CBE r e s u l t s r e c e n t l y published by TSANG [3], t h a t o u r r e s u l t s (AE = 10.5 meV f o r a 1.2 n m well) c o m p a r e f a v o u r a b l y with o t h e r s .

T h e m u l t i p l e p e a k s t r u c t u r e of QW e m i s s i o n l i n e s h a s b e e n previously o b s e r v e d in GaAslGaAlAs QW C51, [6] a n d i s a t t r i b u t e d t o o n e m o n o l a y e r s i z e f l u c t u a t i o n s of t h e well thickness. T h e o b s e r v a t i o n of such a s t r u c t u r e i n d i c a t e s t h a t t h e l a t e r a l s i z e of t h e s e f l u c t u a t i o n s is g r e a t e r t h a t t h e e x c i t o n Bohr d i a m e t e r (300 A ), a n d i n t u r n t h e good q u a l i t y of t h e i n t e r f a c e . On t h e c o n t r a r y if t h e l a t e r a l s i z e of t h e s e d e f e c t s i s s m a l l e r t h a n t h e e x c i t o n Bohr d i a m e t e r , t h e c o n f i n e m e n t e n e r g y f l u c t u a t i o n s i n d u c e a b r o a d e n i n g of t h e e x c i t o n i c l i n e s 161.

S i n c e m u l t i p l e p e a k s t r u c t u r e h a s n e v e r b e e n r e p o r t e d f o r GaInAslInP QW, w e a n a l y s e t e n t a t i v e l y o u r r e s u l t s in t e r m s of t h i c k n e s s f l u c t u a t i o n s .

F r o m f i g u r e 4 which r e p r e s e n t s t h e e n e r g y v a r i a t i o n of t h e d i f f e r e n t p e a k s as a f u n c t i o n of t h e well thickness, w e c a n d e d u c e f o r e a c h w e l l t h e t h i c k n e s s f l u c t u a t i o n t o which c o r r e s p o n d s t h e e n e r g y d i f f e r e n c e b e t w e e n t h e h i g h e r a n d lower e n e r g y peaks. We o b s e r v e t h a t t h i s e n e r g y d i f f e r e n c e c o r r e s p o n d s t o o n e m o n o l a y e r (ao/2) s i z e f l u c t u a t i o n of t h e well. I t c a n however b e n o t i c e d t h a t t h e p h o t o l u m i n e s c e n c e s p e c t r u m of t h e t h i n n e r well shows a n a d d i t i o n a l p e a k (E = 1.121 eV) which c a n n o t b e a t t r i b u t e d t o a m o n o l a y e r s i z e f l u c t u a t i o n . T h i s p e a k c o u l d b e r e l a t e d t o s o m e t r a n s i t i o n involving a n i m p u r i t y s t a t e .

G a x I n l - x P l - y / I n P QW e x h i b i t p h o t o l u m i n e s c e n c e s p e c t r a with l i n e s b r o a d e r t h a n GaInAs/InP QW. A t y p i c a l l i n e w i d t h of 1 8 meV f o r a 1.2 n m t h i c k w e l l i s observed, which i s c o m p a r a b l e t o v a l u e s published by M.B. PANISH for GSMBE q u a n t u m w e l l s

r - i

Acknoledgment

T h e a u t h o r s wish t o t h a n k J. BENOIT f o r u s e f u l discussions.

References

[ I ] W.T. TSANG a n d E.F. SCHUBERT, Appl. Phys. Lett.,

s,

[2] M.B. PANISH, H. TEMKIN, R.A. HAMM, a n d S.N. G. CHU, Appl. Phys. Lett., 9,

1 6 4 (1986)

[3] W.T. TSANG, J. C r y s t a l Growth, 81, 261 (1987)

[4] H. KAWAI, K. KANEKO a n d N. WATANABE, J. Appl. Phys., 56, 4 6 3 (1984) l53 L. GOLDSTEIN, Y. HORIKOSHI, S. TARUCHA a n d H. OKAMOTO, Jpn. J. Appl.

Phys., 22, 1 4 8 9 (1983)

[61 B. DEVEAUD, J.Y. EMERY, A. CHOMETTE, B. LAMBERT a n d M. BAUDET, Appl.

Phys. Lett., 45, 1 0 7 8 (1984)

JOURNAL DE PHYSIQUE

1.6 1.5 1.4 1.3 1.2 1.1 1 .O

WAVELENGTH ( p r n ) 400

& I d s WELL

b E c / ~ E v = 80/20

0 10 20 30

Photoluminescence spectrum Confinement energy vs of CalnAs/lnP quantum wells. well thickness of CaInAs

QW-Solid lines correspond t o a theoretical calcu- lation ( s e e text).

.u BCISE (Tsang c l al.)

-

-1

= ^A

g =-• T : 2 - 6 K

5

W * i).\ ^{\\ A} This work

W '+ /

2 m\ '-'in

'a* ^A

W .

2 5 4 -

3

\

=\

=\.-.-.

P

b Hogher energy peak A. Ittler~~tedtdte peak 0 Lower energy peak

WIDTH OF QUANrllM WliLL LZ (nnl)

Compilation of CalnAs/lnP PL peak energies of CalnAs/lnP MQW QW photoluminescence line- structures with corresponding width widths (after Tsang ,ref 3). fluctuations.