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Toward the Fabrication of Site-controlled

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

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  1. 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

  2. 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

  3. Introduction • Self-assembling Formation of QDs 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.

  4. 100nm Droplet Epitaxy As molecular-beam Ga droplets Ga molecular-beam GaAs Quantum Dots GaAlAs Ga droplets

  5. 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

  6. 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

  7. 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.

  8. 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

  9. 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

  10. 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)

  11. Comparison between experimental and calculated transition energy

  12. 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.

  13. InGaAs QDs determined from the STM image 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

  14. 4.Fabrication of 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)

  15. Improvement of Optical Properties ofAir-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

  16. (a) (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).

  17. AFM image of InAs QDs fabricated by Droplet Epitaxy on a substrate with nano-holes Hole-to-hole distance is 100 nm

  18. 5.Summary 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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