超平坦 GaAs 量子井戸の発光像とスペクトル計測

Ji-Won Oh ， Masahiro Yoshita ， Hirotake Itoh ， Hidefumi Akiyama, Loren PfeifferA ， Ken WestA

Institute for solid state physics, University of Tokyo,and CREST, JST

Bell Laboratories, Lucent Technologies, USA.A

• Novel 　 growth-interrupt annealing technique with a cleaved-edge overgrowth (CEO) method in MBE growth:Atomically flat (110) GaAs quantum well

[1] M. Yoshita , H. Akiyama, L. N. Pfeiffer, K. W. West Jpn. J. Appl. Phys. 40, L252-254 (2001).

• Slight variation in Ga supply results in the formation of characteristic surface step-edge patterns such as 2- or 3-ML high- islands or 1-ML-deep pits

[2] M. Yoshita, H. Akiyama, L. N. Pfeiffer, K. W. West, Appl. Phys. Lett. 81, 49-51 (2002)

Introduction

600 ℃10 min

5X5 m

[3] J. W. Oh, M. Yoshita , H. Akiyama, L. N. Pfeiffer, K. W. West, Appl. Phys. Lett. 82, 1709-1711,2003.

Applied Physics Letters 表紙論文 !

2- or 3-ML high islands

1-ML-deep pits

[110]

[001]

Characteristic Surface Forms on Atomically Flat Surface

Purpose of experiment

Carrier diffusion on atomically flat (110) GaAs /GaAlAs QW and its dependences on temperature (4K-120K) observed by point and uniform optical excitation by Ti-Sa laser (730nm)

Schematic Diagram for PL observation at various sample position & temperatures

PL

AlGaAs

GaAs

10nm10nm

6nm

6.8 m

29% AlGaAs

AtomicallyFlat (110) !

Ti-SaTemp

4K

10K

30K

45K

60K

90K

100K

120K

4K 　 10K 30K 　 45K 60K 80K 100K 120K

25

20

15

10

5

0

706050403020100m

Image of 1-ML Deep Pits

Image and PL spectra of 2-3 ML High Islands

25

20

15

10

5

0

706050403020100 m

　 4K 　 　　 10K 30K 　　　 45K 　 60K 80K 　　100K 120K

8000

6000

4000

2000

0

790788786784782780778776

N=779.62um, N+2=782.34nm N+3= 784.41nm

N

N+2

N+3

25

20

15

10

5

0

706050403020100

Atomically Flat (110) Surface

　 4K 　 　 10K 　 30K 　 　 45K 　 60K 　 80K 　 100K 120K

m

1.0

0.8

0.6

0.4

0.2

0.022201816141210

4K 10K 30K 45K 60K 80K

25

20

15

10

5

0

50403020100

Sliced PL Profiles from Atomically Flat Surface

]1)2//[cosh()]/cosh()2/[cosh()( lLlxlLxI

WidthQWLlengthdiffusionl :: :l )(xI gets thinner

Measurement of Diffusion Length at various low

temperature with point excitation

PL

6.8 m

17

16

15

14

13

17161514

FWHM:0.95m

Reflection image

m

18

17

16

15

14

13

18171615141312

18

17

16

15

14

13

18171615141312

18

17

16

15

14

13

18171615141312

2 2diff obs spot

4K

60K 100K

18

17

16

15

14

13

1817161514131211

30K

m

Spot PL images at various low temperature

16.5

16.0

15.5

15.0

14.5

14.0

13.517.016.015.014.0

spotl

:obsl PL Image

: beam reflection

:Beam Reflection

:diffl diffraction length

Diffusion on Atomically Flat surface

diff

Longer diffusion length

( ' )

cadiff ca

kTD

ekT

D Einstein s equatione

0.7diff m By Hilmer et. al. Phys.Rev. B.42. 3220-3223 (1990)

At 30K ps 4000 2 /cm s

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

Diff

usio

n Le

ngth

(µ

m)

100806040200Temperature (K)

1.7diff m in our data

Conclusion・ Observation of unique surface forms on

atomically flat (110) interface in GaAs/GaAlAs QW via microscopic PL imaging

1-ML-deep pits: dark triangular regions (higher energy regions: carriers flow outside)

2~3 ML-high islands :bright PL spots (lower energy regions: carriers flow inside)

・ Carrier diffusion length in low temp. by point excitation : efficient carrier migration over 1 mm scale even at 4K which increases with temp

・　 Slenderizing PL image with growing temp: well explained by the measureddiff

80m

[001][110]

[110]

30.0 ML

30.X ML

29.X ML

As

Ga

Characterizing top surface of Sample with AFM

3~4

mm

Fabrication of QW sample by cleaved-edge overgrowth

GaAs QW(110)

1

First

MBE growth

Second MBE growth

in situ cleavage

(001)

GaA

s (0

01)

subs

trat

e

By means of cleaved-edge overgrowth method with molecular beam epitaxy and growth interrupt annealing, we fabricated (110) GaAs quantum wells having atomically flat interfaces. We introduced characteristic 1-ML-deep pits and 2~3-ML-high islands on atomically flat interfaces by adding fractional monolayer of GaAs, which are characterized by atomic force microscope (AFM).

In PL observation with uniform excitation, pits are reproduced as dark triangle images due to higher energy than surroundi-ngs and islands as bright PL spots due to lower energy. With increasing temperature, we observe changes in their shape and enhanced contrast, which is explained by enhanced carrier diffusion length due to significant reduction of interface-roughness scattering.

Abstract

a

b

c

e

d

f

24-01-a,b,c

24-02-a,b,c

24-03-a,b,c

24-04-a,b,c

24-05-a,b,c

24-06-a,b,c

24-07-a,b,c

24-08-a,b,c

24-09-a,b,c

24-10-a,b,c

24-11-a,b,c

Block name(arbitrary)

Scan name(arbitrary) Ga24

04-d

11-c

06-c

09-c 10-c

01-b

Ga-24