60 Nanoscale Res Lett (2006) 1:57–61 Fig. 4 (a) AFM image of QD pairs formed after 45 s annealing. (b) A single QD pair formed after 45 s annealing at 590 C performed at substrate temperatures very close to normal MBE growth conditions. Therefore, high quality of GaAs/AlGaAs coherent nanostructures with excellent optical properties is demonstrated by near- ﬁeld scanning optical microscopy. Such studies will be reported in the near future. In summary, by forming Ga droplets and con- verting them into GaAs nanostructures at relatively high temperatures, the evolution of QD pairs is observed during subsequent annealing. The dramatic change in shape is caused by the anisotropy nature of surface diffusion and incorporation. High-temper- ature droplet epitaxy is demonstrated to provide a valuable opportunity to fabricate novel semiconduc- tor nanostructures. Fig. 5 AFM image of surface nanostructures formed after 10 min annealing Acknowledgments We thank Dr. John L. Shultz for his tech- nical assistance regarding the MBE system. References 1. D. Bimberg, M. Grundmann, N.N. Ledentsov, Quantum Dot Heterostructures (Wiley, Chichester, 1999) 2. D. Leonard, M. Krishnamurthy, C.M. Reaves, S.P. DenBa- ars, P.M. Petroff, Appl. Phys. Lett. 63, 3203 (1994) 3. J.M. Moison, F. Houzay, F. Barthe, L. Leprince, E. Andre, O. Vatel, Appl. Phys. Lett. 64, 196 (1993) 4. C.D. Lee, C. Park, H.J. Lee, K.S. Lee, S.J. Park, C.G. Park, S.K. Noh, N. Koguchi, Jpn. J. Appl. Phys. 37, 7158 (1998) 5. K. Watanabe, N. Koguchi, Y. Gotoh, Jpn. J. Appl. Phys. 39, L79 (2000) 6. T. Mano, T. Kuroda, S. Sanguinetti, T. Ochiai, T. Tateno, J. Kim, T. Noda, M. Kawabe, K. Sakoda, G. Kido, N. Koguchi, Nano Lett. 5, 425 (2005) 7. Zh. M. Wang, K. Holmes, J.L. Shultz, G.J. Salamo, Phys. Stat. Sol. (a) 202, R85 (2005) 8. S.S. Li, J. B. Xia, J. L. Liu, F.H. Yang, Z.C. Niu, S.L. Feng, H.Z. Zheng, Pro. Natl. Acad. Sci. 98, 11847 (2001) 9. H. Lee, J.A. Johnson, M.Y. He, J.S. Speck, P.M. Petroff, Appl. Phys. Lett. 78, 105 (2001) 10. S.C. Lee, L.R. Dawson, K.J. Malloy, S.R. Brueck, Appl. Phys. Lett. 79, 2630 (2001) 11. O.G. Schmidt, N.Y. Jin-Phillipp, C. Lange, U. Denker, K. Eberl, R. Schreiner, H. Grabeldinger, H. Schweizer, Appl. Phys. Lett. 77, 4139 (2000) 12. J. Liang, H. Luo, R. Beresford, J. Xu, Appl. Phys. Lett. 85, 5974 (2004) 13. H.Z. Song, T. Usuki, S. Hiros, K. Takemoto, Y. Nakata, N. Yokoyama, Y. Sakuma, Appl. Phys. Lett. 86, 113118 (2005) 14. X. Mei, M. Blumin, M. Sun, D. Kim, Z.H. Wu, H.E. Ruda, Q.X. Guo, Appl. Phys. Lett. 82, 967 (2003)