The control of semiconductor nanostructures is increasingly valuable for the next-generation devices. Density functional theory (DFT) calculations have been playing important roles to clarify the structures of semiconductor surfaces at atomic scale. However, conventional DFT methods can usually treat systems containing less than a thousand atoms, and cannot treat the complex nanostructures. To overcome this problem, we have been developing a linear-scaling DFT code CONQUEST, which can perform structure relaxation or molecular dynamics of 100,000+ atom systems.
In this talk, I will present our large scale DFT study on (1) the growth of Ge 3D nanostructure of Si(001) surface and (2) the atomic and electronic structures of Si/Ge or Ge/Si core-shell nanowires. I will show that CONQUEST can calculate the strain distributions in the actual size of the nanostructures created experimentally. I will also report the unique properties of the electronic structure of Si/Ge or Ge/Si core-shell nanowires.

This work was done in collaboration with Prof. D. R. Bowler, Dr. Sergiu Arapan and Dr. J. Lin, and was partly funded by New Energy and Industrial Technology Development Organization of Japan (NEDO) Grant (P16010).