Study On Growth And Doping Of ZnO Thin Films

In recent years, ZnO has gained substantial interest for its wide applications in short wavelength photonic devices, piezoelectric sensors, transparent conducting films, solar cells and surface acoustic wave devices. Compared with another wide bandgap semiconductor GaN, ZnO has a higher exciton binding energy, better stability and lower cost of production, which has made ZnO experiencing a research boom in the last ten years.At the same time, we also note that the development of ZnO based devices is hindered by lack of reliable and reproductive p-type ZnO. Though much progress has been made by researchers in recent years, there are still some obstacles standing on the way to commercial application of p-type ZnO. In addition, there remains much controversy regarding the intrinsic defects of undoped ZnO. Considering the above background, this dissertation focused on the aspects of crystal growth, structural morphology and p-type doping. The contents can be divided into the followings:1. Under optimal growth conditions, highly oriented ZnO films were prepared using DC magnetron sputtering method. The structural, morphological, optical and electrical properties of undoped ZnO films were investigated. By low temperature PL measurement, the temperature dependence of the optical properties of ZnO films was discussed. The results show that the dominant peak of D°X transition is probably originated from hydrogen.2. Effects of the annealing temperature of ZnO films on the structural and optoelectronic properties were studied in detail. XRD results reveal that post annealing processing can improve the film's quality. XPS shows that ZnO films are well closed to stoichiometry after annealing at 800℃in oxygen ambient. Absorption Spectra reveal the annealed films are of high optical properties. The I-V characteristics show that ZnO/Si heterojunction annealed at 800℃near ideal diode rectifying behavior. 3. Effects of Al₂o₃ buffer layer on the properties of ZnO films were investigated. By introducing Al₂o₃ buffer layer, the mismatch between Si substrates and ZnO films can be effectively reduced and relaxation of the stress is observed. In addition, the Al₂o₃ buffer layer enhances the intensity of UV emission from ZnO films.4. Nitrogen doped ZnO films were realized by thermal oxidation of the Zn₃N₂ films. The relationship between the structural and optical properties of the ZnO:N films and annealing temperature was investigated. XRD results illustrate that the as sputtered Zn₃N₂ films can be transformed into ZnO:N films after annealing at 600℃. XPS results reveal that nitrogen has two chemical states in the ZnO:N films: one is (N₂)_o. donor and the other N_o acceptor. Hall effect measurements demonstrate the decrease of the carrier concentration in the ZnO:N films. FA and DAP transition peaks are observed in low temperature PL spectra of ZnO:N films, from which the nitrogen acceptor binding energy can be obtained. The rectifying characteristics of I-V measurement derived from ZnO homojunctions indicate that the ZnO:N films exhibit a tendency of converting to p-type. Our results provide a theoretical basis and valuable experience.