Nonmetallic nature of In-induced nanoclusters on Si(100)

We have studied the electronic properties of the nanoclusters formed by In on the Si(100) surface by angle-resolved photoemission spectroscopy. The Si(100)4 × 3-In surface, composed of Si₇In₆ nanoclusters, was found insulating with an energy gap of 0.5 eV below Fermi energy. The nanocluster array on this surface induces five different surface states with a characteristic and dominating one within the band gap. The doping of further In onto this surface yields no significant change of the band gap in contrast to the recent scanning tunnelling spectroscopy study reporting metallic cluster formation [Phys. Rev. Lett., 91, 026104 (2003)]. The experimental result is fully supported by first-principles calculations, which reveal both the In-doped (Si₅In₈) and undoped (Si₇In ₆) nanoclusters are insulating with the energy gaps of 0.42 eV and 0.53 eV, respectively.