Researching On Fabricating Reliable And Stable P-type ZnO Films And Its Optical And Electrical Properties

Recently,ZnO has attracted great interest for its wide band-gap(3.37 eV) and relatively large exciton binding energy(60 meV) at room temperature(RT).It has been regarded as one of the most promising candidates for the next generation of ultraviolet(UV) light emitting diodes(LEDs) and lasing devices(LDs) operating at high temperatures and in harsh environments.For the application of ZnO based optoelectronic devices,it is necessary to fabricate both n-type and p-type ZnO films.It is easy to obtain n-type ZnO because it is intrinsic electron-conduction.However,realization of stable and reproducible p-type ZnO has long been the bottle-neck of ZnO-base optoelectronic devices.There are many methods to fabricate ZnO films,for examples,Molecular Beam Eptaixy(MBE),Metal-Organic Chemical Vapor Deposition(MOCVD),Pulsed laser deposition(PLD),ultrasonic spray pyrolysis (USP),Sputtering,and so on.Ultrasonic spray pyrolysis method is used to deposit ZnO film in this thesis because of the advantages of its simplicity,low equipment cost and high deposition rate.ZnO films are studied using X-ray diffraction(XRD),scanning electron microscope(SEM),Hall effect measurements,photoluminescence spectra,and transmittance spectra measurements.1.The effect of substrate temperature on structural,electrical and optical properties of ZnO:Ag films were studied using X-ray diffraction(XRD),Hall effect measurements, photoluminescence spectra,and transmittance spectra measurements.All the measurements were performed at room temperature.It is found that electrical and optical properties of the obtained ZnO:Ag thin films change dramatically due to Ag doping.The Ag doped p-type ZnO films with hole carrier concentration of 5.295×10¹⁵ cm^-3 and Hall mobility of 6.61cm²V^-1s^-1 at room temperature have been successfully obtained at optimal conditions of 500℃.In photoluminescence(PL) measurements,a strong ultraviolet emission centered at 379nm and relatively weak green emission band was observed,and in transmittance measurements,a high transmittance of～70%in the visible region and a sharp absorption edge at 375nm were observed for all samples.2.The ZnO:N-Ag films are deposited on quartz glass substrates by ultrasonic spray pyrolysis technology.Hall-effect-measurement demonstrate that the p-type signals in ZnO films are greatly enhanced by the double acceptor codoping of N and Ag in the same temperature of 500℃,and the N-Ag codoped low-resistivity p-type ZnO film with the resistivity of 1.05Ω·cm,relatively high carrier concentration of 5.43×10¹⁷cm^-3,and mobility of 10.09cm^2.V^-1.s^-1 is obtained.Success in synthesizing p-type ZnO films as reported here confirm that p-type ZnO with acceptable properties for optoelectronic applications can be realized by simultaneous codoping with two potential acceptors.