1. へき開再成長法により作製された(110)GaAs 量子井戸における表面原子ステップの観察
6pSA-12
2002 JPS fall
東大物性研、 Bell Labs. A
呉智元 、吉田正裕 、秋山英文、
Loren Pfeiffer A、Ken West A
Outline:
1. Introduction: Fabrication of T-QWR by COE method
2. Flattening (110) GaAs surface by growth-interrupt annealing
3. Experiment: Characterizing top (110) surface of T-wire
4. Surface morphology of (110) GaAs layer
5. Statistical analysis on the size and shape distribution of fish-shaped pits
6. Mechanism for atomically flat surface formation
7. Summary
In the previous work, we developed a growth-

2. Fabrication of T-shaped QWR by cleaved-edge overgrowth
AlGaAs
GaAs
(110)
First MBE growth
Second MBE growth
in situ cleavage
arm 1
GaAs (001) substrate
stem
(001)
Advantages: available to design QW
freely at atomic scale.
T-wire
First, we grew GaAs and AlGaAs layer on substrate into (001) direction by MBE to make quantum well structures called stem wells. Then cleave sample to expose (110) surface and we grew a 5 ~ 6 nm thick GaAs layer on this in situ cleaved (110) surface to makes arm wells.
In the cross-section of arm well and stem well, T-shaped QWR is made. This structure have advantages to design QWR freely at atomic scale.
However, the cleaved (110) GaAs layer has interface roughness due to critical growth condition of (110) GaAs surface such as
Low growth temperature and high As pressure. This roughness leads to the serious degradation of QW quality.
Rough
ARM
Flat
Disadvantages: MBE growth on (110)
* Critical growth condition: surface
roughness leading to degradation.
STEM

3. Growth-interrupt annealing treatment
Atomically flat surface formation on (110)
GaAs layer by growth-interrupt annealing
(Jpn.J.Appl.Phys. (2001))
Microscopic PL images and spectroscopy
& morphology via AFM of (110) GaAs layer
(Appl. Phys. Lett. (2002))
Application:
The first single wire lasing
(26th ICPS, Edinburgh (2002)
6 nm ( 30　ML-GaAs) (110) GaAs layer before & after annealing
600 oC
10 min
5 mm X 5 mm
In the previous work, we developed a growth-interrupt annealing technique, and measured annealed surfaces of (110) GaAs layer via atomic force microscope (AFM) and photoluminescence imaging. These are AFM images of (110) GaAs layer before and after annealing samples at 600 centigrade degree in ten minutes.
We can see rough surface changed into atomically flat surface.
However, evolution mechanism for flat surface is unclear since in situ observation of surface morphology is difficult during MBE growth.
490 oC growth ?
Mechanism for flat surface formation:

4. Characterizing top surface of T-QW : (110) surface
80mm
29.X ML As
3~4 mm
30.0 ML
[110]
30.X ML Ga
[001]
[110]

5. X
29.26 ML
29.35 ML
29.35 ML
29.55 ML
29.42 ML
29.48 ML
At Minus Deviations

6. P3-06-C
29.58 ML
29.74 ML
29.92 ML
30.09 ML
30.00 ML
30.06 ML
0 and Plus Deviation

7. P3-06-C
30.15 ML
30.19 ML
30.25 ML
30.25 ML
30.27 ML
30.27 ML
At Plus Deviations

8. Plot of a vs.b & a / b ratio vs. fish area

9. Atomic step model and kinetics of surface evolution during annealing

10. Time evolution of 1-ML-deep pits into atomically flat surface
[110]
[001]
[110]

11. Summary
Characterized: atomically flat (110) GaAs surfaces fabricated by the CEO method with growth-interrupt annealing
Statistics of atomic edge stability of 1-ML-deep pits:
large fish: round shape ⇔ small fish: thinner shape !
Ga capping three bonds > Ga capping two bonds
Proposed: model for atomically flat surface
formation.
Note: Atomically flat surface consists of Ga capping three bonds

12. Ga23
01-b
03-c
08-a
13-a
15-b
16-c
Sample: (pos. 2)

13. Ga24
04-d
06-c
01-b
10-c
11-c
09-c
Sample: (pos. 3)

14. Characteristic surface shapes
Spatial distribution of GaAs layer thickness (1 %/mm):
islands & pits on flat surface.
Fish : 1-ML-deep (0.2 nm)
pits at +　deviation.
Boat: 2~3-ML-high islands
at -　deviation.
Arrowheads: 2-ML-deep pits
So, we have a idea of investigating the kinetics of atomic movement by intentionally introducing spatial distribution of GaAs layer thickness.
At integer monolayer, atomically flat surface is formed. However,