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Toward the Fabrication of Site-controlled III-V Compound Semiconductor Quantum Dots by Droplet Epitaxy Nobuyuki Koguchi National Institute for Materials Science  ( NIMS) Tsukuba, 305-0047, Japan. OUTLINE Introduction Droplet Epitaxy 2. Fabrication of GaAs/AlGaAs QDs by Droplet Epitaxy

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Toward the Fabrication of Site-controlled

III-V Compound Semiconductor Quantum Dots by Droplet Epitaxy

Nobuyuki Koguchi

National Institute for Materials Science (NIMS)

Tsukuba, 305-0047, Japan


  • OUTLINE

  • Introduction

  • DropletEpitaxy

  • 2. Fabrication of

  • GaAs/AlGaAs QDs by Droplet Epitaxy

  • 3. Fabrication of

  • In(Ga)As/GaAs QDs by Droplet Epitaxy

  • 4. Fabrication of

  • site-controlled QDs by Droplet Epitaxy

  • 5. Sammary


Stranski-Krastanow Growth

Early 80`s Pioneering Research works on the growth mechanism of InAs/GaAs

B.F.Lewis, F.J.Grunthaner, A.Madhukar, R.Fernandez and J.Maserjian, J. Vac.

Sci. & Technol. B2 (1984) 419

L.Goldstein, F.Glas, J.Y.Marzin, M.N.Charasse and G.Le Roux, Appl. Phys. Lett. 47 (1985) 1099.

D. Leonard, M. Krishnamurthy, C. M. Reaves, S. P. Denbaas

and P. M. Petroff, Appl. Phys. Lett. 63 (1993) 3203.

Droplet Epitaxy

N. Koguchi, S. Takahashi and T. Chikyow, Proceed. 6th Int. Conf. MBE, La Jolla, 1990, J. Cryst.Growth 111 (1991) 688.


100nm

Droplet Epitaxy

As molecular-beam

Ga droplets

Ga molecular-beam

GaAs Quantum Dots

GaAlAs

Ga droplets


Droplet Epitaxy

N. Koguchi, S. Takahashi and T. Chikyow, Proceed. 6th Int. Conf. MBE, La Jolla, 1990,

J. Crystal Growth 111 (1991) 688.

N. Koguchi and K. Ishige, Jpn. J. Appl. Phys. 32 (1993) 2052.

K. Watanabe, N. Koguchi and Y. Gotoh: Jpn. J. Appl. Phys. 39 (2000) L79.

T. Mano, K. Watanabe, S. Tsukamoto, H. Fujioka, M. Oshima and N. Koguchi,

J. Crystal Growth 209 (2000) 504.

QDs both in lattice-mismatched

andlattice-matched systems

QDs with orwithout wetting layer


2.Fabrication of

GaAs/AlGaAs QDs by Droplet Epitaxy

Ga droplets

As4 flux (Torr)

4×10-7

4×10-5

4×10-5

4×10-7

Substrate temperature(℃)

200

200

200

150

150


20

16

12

×1

×28,300

8

GaAs

4

0

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1

295K

20K

AlGaAs

QDs

PL Intensity (arb. units)

HRSEM image of surface morphology of GaAs/AlGaAs QDs.

Photon Energy (eV)

HRSEM images of cross sections of buried QDs after stain etching. QDs are indicated by arrows.


QDs without WL

QDs with X+1.75 MLs WL

c(4×4) As 1.75 MLs

c(4×4) As 1.75 MLs

AlGaAs

x MLs GaAs

1.75 MLs AlGa Supply

AlGaAs

Ga Droplet Formation

Ga Droplet Formation

1.75 MLs AlGaAs

AlGaAs

AlGaAs

1.75 MLs AlGaAs

AlGaAs

Crystallization by As Supply

Crystallization by As Supply

GaAs QDs

GaAs QDs

AlGaAs

1.75 + xMLs GaAs Layer

AlGaAs


S.Sanguinetti et al.

J. Crystal Growth, 253 (2003) 71.

GaAs QDs

without WL

GaAs QDs

With 3 MLs WL

GaAs QDs

With 8 MLs WL


PL spectra of GaAs QDs (20 K)

  • Without WL

  • With 3 MLs WL

  • (1.25MLs MBE + 1.75 MLs DE)

  • With 8 MLs WL

  • (6.25MLs MBE + 1.75 MLs DE)



Excitation power dependence of PL spectra for InGaAs QDs at 20K.

3.Fabrication of

InGaAs/GaAs QDs by Droplet Epitaxy

T.Mano, K.Watanabe, S.Tsukamoto, H.Fujioka, M.Oshima and N.Koguchi, Jpn.J.Appl.Phys.38 (1999)L1009.


InGaAs QDs determined from the STM image 20K.

N.Liu, H.K.Lyeo, C.K.Shih, M.Oshima, T.Mano and N.Koguchi Appl.Phys.Lett.80 (2002).

(a) 250 nm×80 nm STM image of HDE-grown InGaAs QDs acquired at a sample bias of –2.5 V (filled states) and a tunneling current of 0.08 nA; (b) zoom-in view of a InGaAs QD.

(a) Empty state STM image of InGaAs QD acquired at a sample bias of 2.5 V (empty states) and a tunneling current of 0.08 nA; (b) enhanced display of (a) showing individual In atoms; (c) row-by-row In-concentration along the [001] direction of the QD


4.Fabrication of 20K.

site-controlled QDs by Droplet Epitaxy

  • Nano-oxide dots

  • patterning by AFM tip-

  • induced oxidation

  • Nano-holes fromation by

  • using atomic hydrogen

  • (c)Indium droplets

  • deposition on nano-holes

  • fordroplet epitaxy.

(a)

(b)

(c)


Improvement of Optical Properties of 20K.Air-Exposed Regrowth InterfaceEmbedded in GaAs/AlGaAs Quantum Wells by Atomic Hydrogen

J. Su. Kim, M. Kawabe, and N. Koguchi,

Jpn. J. Appl. Phys.43 (1A/B), L103 (2004).

AlGaAs

2nm

GaAs

5nm

3nm

AlGaAs

Air-Exposed Regrowth Interface

  • Air-exposed

  • Without air-exposed


(a) 20K.

(b)

Selective 500 × 500 nm AFM images with cross sectional profileof

the oxide dots patterned by AFM tip-induced oxidation (a)

and the nano-holes after etched by atomic hydrogen (b)

J. S. Kim, M. Kawabe, and N. Koguchi, J. Crystal. Growth 262, 265 (2004).


AFM image of 20K.InAs QDs fabricated by Droplet Epitaxy on a substrate with nano-holes

Hole-to-hole distance is

100 nm


5.Summary 20K.

Droplet Epitaxy

QDs both in lattice-mismatched and

lattice-matched systems

QDs with or without wetting layer

Possibility for fabricating

site-controlled QDs


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