We have grown highly
directional, epitaxial Sn:In2O3 nanowires via
the vapor–liquid–solid mechanism on m-, r- and a-Al2O3 between 800 and 900 °C at 1 mbar. The Sn:In2O3 nanowires have the cubic bixbyite crystal structure
and are tapered with lengths of up to 80 μm, but they are inclined
at ϕ ≈ 60° along one direction on m-Al2O3 while those on r-Al2O3 are inclined
at ϕ ≈ 45° and oriented along two mutually orthogonal
directions. In contrast, vertical Sn:In2O3 nanowires
were obtained on a-Al2O3. We obtain excellent
uniformity and reproducible growth of Sn:In2O3 nanowires up to 15 mm × 15 mm on m- and r-Al2O3, which is important for the fabrication of nanowire solar
cells. All of the Sn:In2O3 nanowires had a resistivity
of 10–4 Ω cm and carrier densities on the
order of 1021 cm–3, in which case the
charge distribution has a maximum at the surface of the Sn:In2O3 nanowires as a result of the occupancy of sub-bands
residing well below the Fermi level, as shown via the self-consistent
solution of the Poisson–Schrödinger equations in the
effective mass approximation. We also show that the Sn:In2O3 nanowires are capable of light emission and exhibited
room-temperature photoluminescence at 3.1 eV as a result of band-to-band
radiative transitions but also at 2.25 eV as a result of donor-like
states residing energetically in the upper half of the energy band
gap. We discuss the advantages of using ordered networks of Sn:In2O3 nanowires in solar cell devices and issues pertaining
to their fabrication.