ZnO nanowire co-growth on SiO2 and C by carbothermal reduction and vapour advection.

Vertically aligned ZnO nanowires (NWs) were grown on Au-nanocluster-seeded amorphous SiO(2) films by the advective transport and deposition of Zn vapours obtained from the carbothermal reaction of graphite and ZnO powders. Both the NW volume and visible-to-UV photoluminescence ratio were found to be strong functions of, and hence could be tailored by, the (ZnO+C) source-SiO(2) substrate distance. We observe C flakes on the ZnO NWs/SiO(2) substrates which exhibit short NWs that developed on both sides. The SiO(2) and C substrates/NW interfaces were studied in detail to determine growth mechanisms. NWs on Au-seeded SiO(2) were promoted by a rough ZnO seed layer whose formation was catalysed by the Au clusters. In contrast, NWs grew without any seed on C. A correlation comprising three orders of magnitude between the visible-to-UV photoluminescence intensity ratio and the NW volume is found, which results from a characteristic Zn partial pressure profile that fixes both O deficiency defect concentration and growth rate.

Electrical characteristics of core-shell p-n GaAs nanowire structures with Te as the n-dopant.

GaAs nanowire (NW)-based p-n photovoltaic devices, with two distinct p and n spatial distributions and where Te was the n-dopant, have been studied by impedance spectroscopy in the 10(3)-10(7) Hz frequency range and the - 1.5-1.5 V bias range. For a large n-core/p-shell overlap region within NWs in a coaxial geometry, the p-n junction properties (DC rectification and p-n depletion capacitance) are found to prevail. The impedance data at low bias for both NW devices show large frequency dispersions with relaxation frequencies that are compatible with carrier re-emission times from traps due to GaAs surface states. An increasing conductance with increasing frequency for low bias is observed, suggesting hopping transport through localized states. For large bias the conductance increases exponentially with bias and is frequency independent, indicating conduction through extended states in this regime.