The Exploration On Electroluminescence Of Doped ZnO Thin Films

Zinc oxide (ZnO), a new semiconductor material with a wide-direct band gap of3.37eV and a large exciton-binding energy of60meV at room temperature, isconsidered as a kind of ideal material for emitting devices in short wavelength due toits effective exciton recombination luminescence at room temperature and hightemperature. In addition, as a kind of semiconductor material, its performance isdetermined by its defects and impurities. Doped ZnO can emit visible light in a widerange, promoting the development from research to application, from material todevices and from lab to factory. In this dissertation, Li:ZnO thin films and Eu:ZnOthin films were firstly prepared on indium-doped tin oxide (ITO) conducting glasssubstrates by sol-gel method, and then their surface morphology, structures andoptical properties were analyzed. At last, we fabricated ZnO EL devices with thestructure of ITO/Doped ZnO thin films/Ag, and their EL properties were also studied.At first, Li:ZnO thin films were prepared on ITO conducting glass substrates bysol-gel method with different doping concentrations and different annealingtemperatures. The effects of different doping concentrations and different annealingtemperatures on the structures and optical properties were also analyzed. The resultsshowed that Li:ZnO thin film was better and uniform when Li mole percent was8%and annealing temperature was560℃. Moreover, the band gap of ZnO thin filmsdecreased and the visible peaks showed red shift as increasing Li concentration. Inaddition, with the increasing temperature, the band gap firstly decreased but thenincreased at the temperature of610℃.The second, Eu:ZnO thin films with different doping concentrations andannealing temperatures were prepared on ITO conducting glass substrates at first. Byanalyzing their structures and optical properties, we found that Eu:ZnO thin filmspresented strong (002) diffraction peak and good quality when Eu mole percent was6%and annealing temperature was550℃. The photoluminescence spectra indicatedthat the intensity of visible peak was strongest when Eu mole percent was6%. Inaddition, the PL spectra presented two sharp peaks at594nm and614nm at lowannealing temperature, which respectively originated from the emission of5D70â†'F1and5D0â†'7F2in Eu3+. At last, we fabricated ZnO EL devices with structures of ITO/ZnO thin film/Ag,ITO/Li:ZnO thin film/Ag and ITO/Eu:ZnO thin film/Ag, respectively, and observedluminescence phenomenon in the devices. I-V curve and EL spectra were alsomeasured and analyzed. In ITO/ZnO thin film/Ag device, I-V curve had goodrectification characteristic and there were two broad visible peaks at485nm and595nm in EL spectra. Moreover, in ITO/Eu:ZnO thin film/Ag device, when Eu molepercent was6%, I-V curve also had rectification characteristic and sharp peaks at580nm,593nm,602nm and broad peak at602nm appeared in EL spectra, owing toEu3+and ZnO defects.