THE TEMPERATURE CHARACTERISTICS OF THE PHOTOLUMINESCENCE FROM GaAs-GaAlAs MULTIPLE QUANTUM WELL STRUCTURES

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THE TEMPERATURE CHARACTERISTICS OF THE PHOTOLUMINESCENCE FROM GaAs-GaAlAs

MULTIPLE QUANTUM WELL STRUCTURES

W. Ge, Z. Xu, Y. Yan, J. Zu, Z. Zheng, D. Sun

To cite this version:

W. Ge, Z. Xu, Y. Yan, J. Zu, Z. Zheng, et al.. THE TEMPERATURE CHARACTERISTICS OF THE PHOTOLUMINESCENCE FROM GaAs-GaAlAs MULTIPLE QUANTUM WELL STRUCTURES.

Journal de Physique Colloques, 1987, 48 (C5), pp.C5-131-C5-134. �10.1051/jphyscol:1987524�. �jpa-

00226728�

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Colloque C5, suppl6ment au noll, Tome 48, novembre 1987

THE TEMPERATURE CHARACTERISTICS OF THE PHOTOLUMINESCENCE FROM GaAs- GaAlAs MULTIPLE QUANTUM WELL STRUCTURES

W.K. GE, Z.Y. XU, Y. YAN, J.Z. ZU, Z.B. ZHENG and D.Z. SUN Institute of Semiconductors, Academia Sinica, P.O. Box 912, Bei jing, China

Abstract.- The temperature behavior of the photoluminescence from GaAs-GaAIAs multiple quantum well structures indicates that the maintaining of the excitonic properties of the luminescence at higher temperature is a good assessment of the material quality, and the temperature dependence of the luminescence intensity ratio from the intentionally arranged wide and narrow wells is discussed by the vertical transport process of the photoexcited electrons.

The luminescence mechanism is one of the most fundamental properties governing the performance of quantum well opto-electronic devices, The previous studies of photoluminescence( PL ) h a y sielded valuable, but controversial interpretations on this probl~m

' .

In this paper we reportadetailed investigation of the temperature behavior of PL from GaAs-GaAlAs multiple quantum we1 Z(MC2W) structures. Our results show that at low temperature, the PL from MQW is excitonic: in nature, but the intrinsic exciton may thermally dissociate and consequently the free carrier recombination becomes predominant. The dissociation temperature of the exciton varies from sample to sample, depending on the material quality. We have also studied the temperature dependence o f the PL spectra from MQW consisting of wide and narrow wells. The

luminescence intensity ratio from wide and narrow wells has been found to be temperature dependent and understood by considering the transport process of the photoexcited electrons.

The investigated samples were grown by a home-made molecular beam epitaxy(MBE) system on (100) GaAs substrate and studied using a con- ventional photoluminescence technique. Fig. 1 shows the peak energy position of the n=l electron-heavy hole recombination(den0ted as Elh) vs temperature for two different samples, For a high quality sample (curve 1). which presents very sharp spectrum with the full width at half maximum(FWHM) as narrow as 1.2 m e V at 11K, Elh follows GaAs band gap Eg (GaAs) very closely. However, for the sample with poor quality

(curve 2), from which both broader intrinsic luminescence(FWHM of 9meV) and relatively strong impurity-related extrinsic luminescence were observed3, Elh peak obviously does not closely follow Eg(GaAs).

For the sake of comparison the Eg(GaAs) curve was redrawn to coincide with curve 2 at low temperature, as indicated by the dashed line in Fig. 1. It is observed that the difference between the toso curves varies as temperature is changed. At temperatures above 200K the

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987524

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C5-132 JOURNAL DE PHYSIQUE

energy d i f f e r e n c e i s a b o u t 8 m e V

I I which i s i n good agreement ?.rltt:

t h e e x c i t o n b i n d i n g energy g i v e n by Greene e t a14. T t is t h e n r e a s o n a b l e t o s u g g e s t t h a t

-

t h e PL e m i s s i o n p r o c e s s v a r i e s from t h e i n t r i n s i c e x c i t o n i c r e c o m b i n a t i o n a t low tempera-

-.-&

t u r e t o free c a r r i e r recombina- t i o n a t h i g h t e m p e r a t u r e , I n t h e t e m p e r a t u r e r a n g e o f l O O K t o 200K, b o t h p r o c e s s e s a r e i n v o l v e d . N e v e r t h l e s s t h e y a r e n o t c l e a r l y i d e n t i f i e d i n t h e

-

s p e c t r a d u e t o t h e t h e r m a l b r o a d e n i n g e f f e c t . The above i d e n t i f i c a t i o n has been con- f i r m e d by t h e e x c i t a t i o n depen- d e n c e o f F't, i n t e g r a t e d i n t e n s i -

I I I t i s n o t e d t h a t t h i s t e m -

I

100 200 300

perature b e h a v i o r c a n be u s e d t o c h a r a c t e r i z e d t h e m a t e r i a l

T ( K 1

q u a l i t y . The i n f l u e n c e o f ma- t e r i a l a u a l i t v on t h e e x c i t o n i c p r o p e r t i e s can be u n d e r s t o o d energy Of E ~ h peak

t h r o u g h two a s p e c t s , F i r s t , a v s t e m p e r a t u r e f o r two different non-uniform distribution of im-

samples

.

p u r i t y may i n t r o d u c e l o c a l

e l e c t r i c f i e l d , which w i l l f a c i - l i t a t e t h e d i s s o c i a i o n o f e x c i t o n d u e t o s p a t i a l s e p a r a t i o n o f t h e e l e c t r o n s and holes'. Secondly, t h e d e g r a d a t i o n o f t h e i n t e r f a c e smoothness p r o v i d e s more t r a p p i n g c e n t e r f o r c a r r i e r s , c o n s e q u e n t l y d e n y i n g t h e f o r m a t j o n o f e x c i t o n .

W e have, i n g r e a t e r d e t a i l , i n v e s t i g a t e d t h e t e m p e r a t u r e dependence o f t h e FL s p e c t r a from quantum w e l l s t r u c t u r e s c o n s i s t i n g of wide and n a r r o w w e l l s . A v e r y i n -

t e r e s t i n g f e a t u r e i n t h e

2

s p e c t r a i s t h e c o m p e t i t i o n

4

^sample⁸⁶⁰³¹

between Iw and IN where

-

I W a n d I N a r e t h e i n t e g r a -

t e d luminescence i n t e n s i -

;

t i e s o f t h e wide w e l l s and

z

n a r r o w w e l l s , r e s p e c t i v e l y . T h i s c o m p e t i t i o n i s found

z

t o b e t e m p e r a t u r e depen-

-

d e n t . Fig.2 shows t h e PL s p e c t r a o b t a i n e d from s a m p l e 86031 a t d i f f e r e n t t e m p e r a t u r e s . The sample i s a s e p a r a t e - c o n f i n e - m e n t o s t r n c t u r e w i t h f i v e

1 4 1 A w s l l s ( rown f i r s t ) a n d o n e 190

3

w e l l s e p a - r a t e d by 70 R G a 0 . 8 A l ~ . ~ A s

b a r r i e r s , sandwiched

11x2 246 _1.50 1.54

between Gao, 6A10.

es

c l a d - d i n g l a y e r s . F1g.3 i s

o b t a i n e d from sample 85049,

ENERGY (eV)

which a l s o i s a s e p a r a t e - Fig.2 Photoluminescence s p e c t r a from c o n f i n e m e n t s t r u c t u r e w i t h s a m p l e 86031 a t d i f f e r e n t temperatures.

a l t e r n a t i v e 1 0 wide w e l l s (LZ=87 A ) and 10 narrow

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w e l l s f L Z = 4 0

8 ) ,

s e p a r a t e d by 1 0 0

%

G ~ o . ~ A ~ o , ~ A s b a r r i e r s and sandwiched between Gw, gA10,qAs c l a d - d i n g l a y e r s . For c l a r i t y , t h e lumi- n e s c e n c e c o m p e t i t i o n i s c h a r a c t e r -

i z e d by t h e r a t i o R = I ~ / I N , and t h e t e m p e r a t u r e dependence o f R f o r s a m p l e s 86031 and 85049 i s p l o t t e d i n Fig.4 and Fig.5, r e s p e c t i v e l y .

T h e e x p e r i m e n t a l r e s u l t s a r e a n a l y z e d by c o n s i d e r i n g t h e p r o c e s s o f e l e c t r o n d i f f u s i o n a c r o s s t h e quantum w e l l w h i l e undergoing LO phonon s c a t t e r i n g . Assuming t h e i n i t i a l eqergy d i s t r i b u t i o n o f e l e c t r o n s a t o n e boundary o f a w e l l t o b e n ( E ) , t h e n t h e energy d i s t r i - b u t i o n of e l e c t r o n s a f t e r t r a n v e r - s i n g w e l l width LZ i s g i v e n by

w h e r e E

Is

t h e e l e c t r o n energy, Ep i s t h e p r o b a b i l i t y o f an e l e c t r o n l o s i n g e n e r g y Ep i n t r a v e r s i n g t h e

1.55 1-60 1.65

d i s t a n c e Lz. By u s i n g F e r m i t s " a g e t h e o r y f p 7 , p ( c a n be deduced from

ENERGY( eV)

Boltzman t r a n

'PI

p o r t e q u a t i o n @ * 9

Fig.3 F h o t o l ~ i n e s c e n c e spectra

P ( E ~ ) = c o ~ s ~ ( $ ) - ~ / ~ ~ x P - ( ~ ~ ~ Z ~ E ) /

from sample 85049 a t d i f f e r e n t

t e m p e r a t u r e , showing t h e l r u n i - (

44FT

⁾ ^{( 2 )}

n e s c e n c e c o m p e t i t i o n phenomenon where

Lp

is t h e mean free path for s c a t t e r i n g , and &E i s t h e mean e n e r g y l o s s p e r c o l l . i s i o n , w h i l e Lp(in

8 )

and S E ( i n meV) a r e g i v e n by

~ ~ " 6 3 . 6

(ep-1

⁾/ ( eS+1) ( 3 )

& ~ = 3 6 ( e p - l ) / ( e P + l ) ( 4

I n t h e c a l c u l a t i o n s , t h e i n i t i a l d i s t r i b u t i o n o f e l e c t r o n s a t t h e boundary o f t h e f i r s t w e l l c o u l d b e d i f f e r e n t due t o d i f f e r e n t sample s t r u c t u r e s . For sample 85049,

w h e r e Ec i s t h e c o n d u c t i o n band edge o f t h e c l a d d i n g l a y e r , and T i s l a t t i c e t e m p e r a t u r e , The r e s u l t a n t d i s t r i b u t i o n i s t a k e n a s t h e i n i - t i a l s i t u a t i o n f o r t h e n e x t w e l l and can b e d e s c r i b e d by an appro- x i m a t e f u n c t i o n

w h e r e B i s a n a d j u s t a b l e parameter, i s a s h a r p edge o f h i g h energy.

C o n s e q u e n t l y w e can n u m e r i c a l l y c a l c u l a t e t h e energy d i s t r i b u t i o n s i n a l l w e l l s . The e l e c t r o n s c o l l e c t e d by e a c h w e l l c a n b e e s t i m a t e d b a s e d o n t h e assumption t h a t t h o s e e l e c t r o n s w i t h E c O ( i.e. below t h e b o t t o m o f t h e c o n d u c t i o n band o f t h e b a r r i e r l a y e r ) are c o l l e c t e d by t h e c o r r e s p o n d i n g w e l l s . A s a r e s u l t , t h e luminescence i n t e n s i t y r a t i o

I W / I N i s o b t a i n e d . The r e s u l t s a r e shown i n Fig.4 and Fig.5 i n dashed c u r v e s .

From t h e comparison between e x p e r i m e n t a l r e s u l t s and c a l c u l a t e d o n e s , i t i s o b v i o u s t h a t t h e above s i m p l e model a l o n e c a n n o t be a p p l i e d t o e x p l a i n t h e e x p e r i m e n t a l r e s u l t s . The d i s c r e p a n c y i s p r o b a b l l y due t o t h e i n a p p r o p r i a t e n e g l e c t o f t h e phonon a s s i s t e d t u n n e l i n g e f f e c t ,

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C5-134 JOURNAL DE PHYSIQUE

Fig.4TheratioRof

3

PL intensity from

wide wells to that

e

from narrow wells vs temperature for sample

86031.

2 - _/'

&

<

+ .

- I P

^p-0-0-

^I ^I

I I

sample 86031

I I

CY

- ^Sample ⁸⁵⁰⁴⁹

2 -

I I

Fig.5 The ratio R of PL intensity from wide wells to that from narrow wells vs temperature for sample 85049.

temperature dependence of carrier lifetime, and different sample con- ditions(interface, residual impurity etc.). The detailed investigation is under progress.

Acknowledgement- We are very grateful to Prof .M.Y .Kong,Drs .D.Z.Sun, J.B.Liang, Z.G.Chen and Y.P.Zhen for sample preparation. This work is supported by the National Science Foundation.

References-

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J. E. fougu&t and A . E.Seigman, Appl. Phys. Lett .46, 280(1985).

Z.Y.Xu, Z.G.Chen, D.Teng, W.H.Zhuang, J.Y.Xu, J.Z.Xu, B.Z.Zhen, J.B.Liang, and M.Y.Kong, Surface Science

174,

216(1986).

R.C.Greene and K.K.Bajaj, Solid State Commun. 4 5 , 831(1983).

Z.Y.Xu, J.Z.XU, W.K.Ge, B.Z.Zheng, J.Y.Xu and Y.Z.Li, Solid State Commun. 6l,707(1987).

E.E.Mendez, G.Bastard, L.L.Chang, L.Fsaki, H.Morkoc and R.Fisher, Phys. Rev.

Q,

7101(1982).

D.J.Bartelink, J.L.Moll, and N.I.Meyer,Phys.Rev.e,972(1963).

N.Holonyark,Jr., R.M.Kolbas,R.D.Dupuis, and P.D.Dapkus, IEEE J. of Quan.Electron -,170(1980).