Sol-Gel Derived Al-Ga Co-Doped ZnO Thin Films Embedded with Microrods.

Aluminium­gallium (Al­Ga) co-doped ZnO (AGZO) thin films with different Al­Ga at.% were spin coated on glass substrates using sol­gel spin coating technique. Morphological images by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) reveal that the granular structures of co-doped films are embedded with microrods, which has never been reported before. The density of the microrods increases with higher co-doping at.%. The Hall Transport measurements reveal that the electrical properties of the co-doped films are comparable with single Ga doped ZnO films, which implies that the co-doping method can be a way forward to reduce the fabrication cost of the doped ZnO films involving expensive raw material. Also, the unique features of the AGZO films embedded with microrods may create new opportunity for these films to be implemented in emerging optoelectronic devices such as solar cells and organic light emitting diodes.

Determination of acceptor concentration, depletion width, donor level movement and sensitivity factor of ZnO on diamond heterojunction under UV illumination.

The concentration of acceptor carriers, depletion width, magnitude of donor level movement as well as the sensitivity factor are determined from the UV response of a heterojunction consisting of ZnO on type IIb diamond. From the comparison of the I-V measurements in dark condition and under UV illumination we show that the acceptor concentration (∼10(17) cm(-3)) can be estimated from p-n junction properties. The depletion width of the heterojunction is calculated and is shown to extend farther into the ZnO region in dark condition. Under UV illumination, the depletion width shrinks but penetrates both materials equally. The ultraviolet illumination causes the donor level to move closer to the conduction band by about 50 meV suggesting that band bending is reduced to allow more electrons to flow from the intrinsically n-type ZnO. The sensitivity factor of the device calculated from the change of threshold voltages, the ratio of dark and photocurrents and identity factor is consistent with experimental data.

Ohmic-rectifying conversion of Ni contacts on ZnO and the possible determination of ZnO thin film surface polarity.

The current-voltage characteristics of Ni contacts with the surfaces of ZnO thin films as well as single crystal (0001) ZnO substrate are investigated. The ZnO thin film shows a conversion from Ohmic to rectifying behavior when annealed at 800°C. Similar findings are also found on the Zn-polar surface of (0001) ZnO. The O-polar surface, however, only shows Ohmic behavior before and after annealing. The rectifying behavior observed on the Zn-polar and ZnO thin film surfaces is associated with the formation of nickel zinc oxide (Ni1-xZnxO, where x = 0.1, 0.2). The current-voltage characteristics suggest that a p-n junction is formed by Ni1-xZnxO (which is believed to be p-type) and ZnO (which is intrinsically n-type). The rectifying behavior for the ZnO thin film as a result of annealing suggests that its surface is Zn-terminated. Current-voltage measurements could possibly be used to determine the surface polarity of ZnO thin films.