Dynamic behavior of two-dimensional exciton in GaAs single quantum well under a magnetic field

Journal of Luminescence 40&41 (1988) 729 730 North-Holland, Amsterdam

729

DYNAMIC J3EHAVIOR OF rI~O_DIMENSIONAL EXC~IONIN GaAs SINGLE QUAN’IUM WELL UNDER A MAGNETIC FIELD Yusaburo SEGANA, Junichi IcUSANO, Yoshinobu AOYAGI, and Susumu NAMBA The Institute of Physical and Chemical Research Ilako-shi, Saitama 351 -01, Japan

Time-resolved photoluminescence spectra of two dimensional excitons in a GaAs single quantum wol 1 were investigated in a magnetic field. The radiative life-time was in~=~eriJi~ of the magnetic field up to 6 T. The high density excitation effect on the photoluminescence spectrum was observed. The ~xciton t~nr~rature was decreased by applying the magnetic field.

Photoluininoscence spectra of two dimensional excitons in a GaAs single quantum well (SOW)

2. With s. The peak power was 0.875 KY/cm increasing I3~_fie1d, the life times of the peak

have

and the total luminescences were not changed

been

studied

under a magnetic field

i~rp~ndicu1arto the hetero interface (the B~field). The sample was a GaAs/Al 0 3Ga0 7As SQU

noticeably,

the peak luninescence

at B~=6T and at B~=0T

grown by :1130. and the well width was 10 nm. The

were

254

radius of the ground cyclotron orbit and the

respectively.

magnetic

our experimental

field

strength

of

the

(0.067m0) at 6 T are calculated

electron

to be 10.5

ii~~

Steady-state excitons

at

be

Therefore,

ps

and

234

ps,

it is concluded from

results

that the radiative

time

excitons in a quantum well is very complicated.

10

13 ar”

heavy-hole

shown in Fig.1.

The

of

free

the optical property of 2-D excitons is

similar

to that

of bound excitons

in a bulk

of 2-D excitons and is

proportional to the icS ft

~

field)2. a

Such a the ~ve

>-

B=6T

space. Therefore, the oscillator strength the heavy-hole

strength

to the

were tos~rved.This shift IS attrinuted diamagnetic shift

If

osci 1 lator

life-

photoluminescence spectra due to of

and the

between the radiative

recombination

was a cw Tie-Ne laser 2. (632.8 A shiftnn)of with the aluminescence focused power of 160 mW/cm photon energy toward the high

of

to

The relationship

excitation

real

found

of

life time is independent of the B~_field.

and 10.4 meV, resoectively. the raliative

as shown in Fig.2. The life-times

exciton is

increased

by

B4T a.

applying the i3~_field. Time resolved photoluminescence spectra were obtained by using a cw-nodelocked Kr

B=OT 1.52

laser

I

1.53

I

1.54

ENERGY(eV)

(647.1 nm) and a synchroscan streak camera. The

FWIIII of the ~r lasor pulse was observed

to he

200 ps when the accumulation tise was about 64

0022 2313/88/$03.50 © Elsevier Science Publishers By. (North-Holland Physics Publishing Division)

FIGURE 1 Photolununescence

I3~_field.

spectra as a function of the

730

Y Segawa el al.

400

I

I

I

/

Dynamic behavior oftwo-dimensional exci/on

I 200

-

~300~~

•

~200-

¶ ¶ ~ ~

~100

i~o-

(ti)

.

4,~• 0 0

~(a)

I 0

I

I

I

34

I

+

I

-

I

I

56

4.

Cc)

-

0

2

4

6

MAGNETIC FIELD(T) MAGNETIC FIELD (T)

FIGURE 3

FIGURE 2

Radiative life—times as a function of the field.

B~-

(•)

represents the life-time of the peak total photonluminescence. energy and Ce) represents that of the the radiative life time is inversely

crystal,

proportional

to the oscillator

strength.1

On the

2-D exciton temperatur~. The excitation power was (a)2. 8.75 KY/cm

,

(h) 0.875 KY/cm

2laser ,

and

Cc) 160 mW/cm states. The radiative transition probability is

independent of the TT~-field. Discrete Landau

contrary, applying the exciton polariton mcxiel,2

levels are generated in a subband and a

the radiative life-time is proportional to (the

degeneracy in

oscillator strength)h/5. The diamagnetic shift

Therefore,

of the

the lowest Landau level.

heavy-hole

enhancement

exciton

indicates

the

of the oscillator strength. However,

discrete

the density

of states

occurs.

the 2-13 exciton band is formed below

distribution

It is thought that the in K 5, K,~,space may cause

the enhancement may be so small that the change

the narrowing observed in the 2-D exciton band.

in the radiative life-time is not caused by the

Onc

Ba-field.

probability for large KX_K~~which exists between Landau levels, decreases with increasing

The narrowing of the luminescence band width

was observed

with

increasing

B5-field.

phenomena is caused by the alteration

This of the

suggestion

is

that

the occupation

B5-fiold. This may cause the cooling phenomenon illustrated in Fiq.3.

higher energy side. Since the intensity at the high energy side has a single exponential decay,

the exciton temperature can be estimated by the -

Boltzmann distribution

function.

The exciton

temperature was reduced applying the B~ field,

RFFERENCES 1.C.l-l.Henry and K.Nassau, Phys.Rev.B 1 (1970)

as shown in Fig.3.

The intensity of the photoluminescence at low temperature transition

is

related

probability

to

the

radiative

and the density

of

2. Y.Toyozawa, Prog.Theor.Phys.

12 (1959) 111.