Enhancement of light extraction from an integrated ZnO nanotips/GaN light emitting diode (LED) is demonstrated. The device is composed of a GaN LED with a Ga-doped ZnO (GZO) transparent conductive layer and ZnO nanotips grown on GZO for light extraction. The light output power of a ZnO nanotips/GZO/GaN LED exhibits 1.7 times enhancement, in comparison with a conventional Ni∕Au p-metal LED. The higher emission efficiency is attributed to the enhanced light transmission and scattering in the ZnO∕GaN multilayer.

ZnO thin-film transistors (TFTs) were built on glass substrates. The device with a top gate configuration operates in the depletion mode. The ZnO channel was grown by metalorganic chemical vapor deposition (MOCVD) on glass at low temperature. SiO 2 was used as the gate dielectric. The TFT has an on/off ratio of $4.0 · 10 4 and a channel field-effect mobility of $4.0 cm 2 /V s. The average transmittance of the ZnO film in the visible wavelength is $80%. To compare the characteristics of the TFTs prepared by using a poly-ZnO and epitaxial-ZnO channel, an epi-ZnO TFT with the same configuration and dimensions was made on an r-Al 2 O 3 substrate. The epi-ZnO TFT shows higher field-effect mobility of $35 cm 2 /V s and on/off ratio of $10 8 .

Surface wettability is an important property of solid/liquid interfaces. Recently, the control of contact angle (CA) has been used to drive liquid droplets in microor nanosize channels on biochemical and environmental sensing chips, where a faster CA transition rate is desirable for the prompt control of liquid movement. We studied the CA between water droplet and zinc oxide (ZnO) nanotips grown by metalorganic chemical vapor deposition (MOCVD). ZnO was grown as epitaxial films on r-plane sapphire, or as vertically aligned nanotips on various substrates, including silicon, c-plane sapphire, and glass. It is demonstrated that by using ultraviolet (UV) illumination and oxygen annealing, the CA on ZnO nanotips can be changed between 0°and 130°, whereas the CA on the ZnO films only varies between 37°and 100°. The fast transition rates also have been observed.

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.