ZnO(Zinc Oxide) is oxide semiconductor with wide direct bandgap(3.4 eV). It is promising Ⅱ-Ⅵ compound semiconductor for utilization in optoelectronics devices. ZnO usually shows n-type characteristics due to various defects. n-type defects make p-type doping very difficult, since acceptor doping should compensate all the n-type defects.
We developed a new method to realize enhancement-mode ZnO thin-film transistors (TFT) and studied effect of N2O and GaAsdoping in ZnO by metalorganic chemical vapor deposition (MOCVD). We used growth interruptions during MOCVD to encourage complete oxidation of deposited ZnO film. With this method, turn-off characteristics were significantly improved, and threshold voltage was shifted to positive voltage.
Capacitance data showed that there is significant carrier depletion at the ZnO/dielectric interface, and that the depletion was sensitive to vacuum annealing. Capacitance measured in N2O doped ZnO increased at negative gate voltages, which indicates positive charge increase in ZnO.
