Kengo Nishio, Taisuke Ozaki, Tetsuya Morishita, Wataru Shinoda, and Masuhiro Mikami
Phys. Rev. B 77 075431(2008).
Recent study has suggested the possible existence of polyicosahedral Si nanostructures which composed of linked icosahedral Si nanodots. The polyicosahedral Si nanostructure has a Si20 fullerene cage per icosahedral Si nanodot. It is expected that the properties of the polyicosahedral Si nanostructure can be tuned by encapsulating appropriate guest atoms into the Si20 cages. In order to clarify the possibility, we carried out a systematic first-principles study on the effects of the encapsulation of Na and I atoms on the electronic and optical properties of the icosahedral Si100H60 nanodot, polyicosahedral Si175H90 nanodot, and polyicosahedral Si150H60 nanowire. Our results show that the nature of the electronic structure, the band gap energy, the radiative recombination rate via the optical dipole transition strongly depend on the number of the icosahedral Si nanodots linked together, the guest atom, the doping ratio, and the doping pattern. The comparison of the electronic band structure of the guest-free polyicosahedral Si nanowire with the similar-size pentagonal Si30H10 nanowire and crystalline diamond Si45H20 nanowire reveals that the band gap energy and the effective masses of the Si nanowire strongly depend on the arrangement of Si atoms. The tunable electronic and optical properties make the polyicosahedral Si nanostructure suitable for the building blocks of the future nanoscale Si-based devices.