ZnO nanotips grown on Si substrates by metal-organic chemical-vapor deposition

The ZnO nanotips are grown on silicon and silicon-on-sapphire (SOS) substrates using the metal-organic chemical-vapor deposition (MOCVD) technique. The ZnO nanotips are found to be single crystal and vertically aligned along the c-axis. In-situ Ga doping is carried out during the MOCVD growth. The ZnO nanotips display strong near-band edge photoluminescence (PL) emission with negligible deep-level emission. Free excitonic emission dominates the 77-K PL spectrum of the as-grown, undoped ZnO nanotips, indicating good optical properties and a low defect concentration of the nanotips. The increase of PL intensity from Ga doping is attributed to Ga-related impurity band emission. Photoluminescence quenching is also observed because of heavy Ga doping. ZnO nanotips grown on Si can be patterned through photolithography and etching processes, providing the potential for integrating ZnO nanotip arrays with Si devices.