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-

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

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:

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]

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

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

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

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

Atomic step model and kinetics of surface evolution during annealing

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

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

Ga23 01-b 03-c 08-a 13-a 15-b 16-c Sample: 5-18-00.2 (pos. 2)

Ga24 04-d 06-c 01-b 10-c 11-c 09-c Sample: 5-18-00.2 (pos. 3)

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,