Epitaxial highly ordered Sb:SnO₂ nanowires grown by the vapor liquid solid mechanism on m-, r- and a-Al₂O₃

Epitaxial, highly ordered Sb:SnO₂ nanowires were grown by the vapor-liquid-solid mechanism on m-, r- and a-Al₂O₃ between 700 °C and 1000 °C using metallic Sn and Sb with a mass ratio of Sn/Sb = 0.15 ± 0.05 under a flow of Ar and O₂ at 1 ± 0.5 mbar. We find that effective doping and ordering can only be achieved inside this narrow window of growth conditions. The Sb:SnO₂ nanowires have the tetragonal rutile crystal structure and are inclined along two mutually perpendicular directions forming a rectangular mesh on m-Al₂O₃ while those on r-Al₂O₃ are oriented in one direction. The growth directions do not change by varying the growth temperature between 700 °C and 1000 °C but the carrier density decreased from 8 × 10¹⁹ cm^-3 to 4 × 10¹⁷ cm^-3 due to the re-evaporation and limited incorporation of Sb donor impurities in SnO₂. The Sb:SnO₂ nanowires on r-Al₂O₃ had an optical transmission of 80% above 800 nm and displayed very long photoluminescence lifetimes of 0.2 ms at 300 K. We show that selective area location growth of highly ordered Sb:SnO₂ nanowires is possible by patterning the catalyst which is important for the realization of novel nanoscale devices such as nanowire solar cells.