Electronic and optical properties of polyicosahedral Si nanostructures: A first-principles study

In a previous molecular dynamics study, we predicted a polyicosahedral Si nanostructure which has a Si-20 fullerene cage per icosahedral Si-100 nanodot. The unique cage structure is distinct from the crystalline diamond Si nanostructure. Encapsulating a guest atom into the Si-20 cage allows us to tune the electronic and optical properties. Here, we report on a systematic first-principles study of the effect of the sodium and iodine doping on the physical properties of the hydrogen-terminated polyicosahedral Si nanostructures. Our calculations reveal the strongly guest-dependent and size-dependent physical properties of the polyicosahedral Si nanostructures: (1) the semiconducting guest-free polyicosahedral nanowire becomes metallic by the sodium and iodine doping, (2) the quantum confinement effect is observed in the icosahedral and polyicosahedral nanodots, and (3) the radiative recombination rate comparable to the luminescent amorphous Si nanostructures is expected from some of the Na- and I-doped polyicosahedral nanostructures. From these results, we assert that the polyicosahedral Si nanostructures are promising candidates for the building blocks of the future nanoscale optoelectronic devices.