Study On Structure, Surface Morphology And Optical Property Of Doped ZnO Thin Films

ZnO is a direct and wide band gap semiconductor materials，and possesses highexcition binding energy, excellent photoelectric performance, good gas-sensitiveproperty, high chemical stability and thermal stability. Naturally, the electrical andoptical properties of intrinsic ZnO thin films is low, therefore, it is necessary toimprove the optical and electrical properties of ZnO thin films by doping andoptimizing process conditions of preparation, which makes it used for optoelectronicdevices. In this paper, Al-doped, Mg-doped, Mg-Al co-doped ZnO thin films and itscomposite thin films were prepared on quartz glass substrates via sol-gel method andmodified Pechini method. The structure, surface morphology and optical property ofthe product films were studied. The main research contents and results are given asfollows:(1) The effects of sol concentration, Al doping concentration, annealingtemperature and film thickness on microstructure and optical property of Al dopedZnO (AZO) thin films were studied. The results showed that Al doping did not changethe crystal structure of ZnO thin films, and the crystal quality of AZO thin filmsdecreased with increasing Al doping concentration. The average optical transmittanceof AZO thin films was over90%in the visible region. The optical band gap of AZOthin films increased from3.283eV to3.352eV, when Al doping concentrationincreased from0%to9%. Room temperature photoluminescence spectra showed thatthe defect emission peak of AZO thin films blue-shifted from orange emissioncentered at610nm to yellow emission located at584nm with increasing Al dopingconcentration.(2) The effects of sol concentraon, Al doping concentration, annealingtemperature and film thickness on microstructure and optical property of Mg-Alco-doped ZnO (MAZO) thin films were studied. The results showed that Mg-Alco-doping also did not change the crystal structure of ZnO thin films. The productfilms possessed preferred orientation growth along (101) plane, and the crystallinesize increased from20.58nm to42.26nm, when annealing temperature increased.EDS spectra demonstrated the presence of Zn, Mg, Al, O elements in the MAZO thinfilms. The optical band gap of MAZO thin films decreased from3.348eV to3.304eVwith increasing annealing temperature from500C to800C. Room temperaturephotoluminescence spectra showed that the UV emission peak red-shifted from372 nm to379nm, and the visible emission peak blue-shifted from yellow-orangeemission centered at598nm to green emission located at527nm with increase inannealing temperature.(3) The microstructure and optical property of MAZO/ZnO and MAZO/AZOmultilayer films were investigated. XRD results showed that MAZO/AZO compositefilms had preferred orientation growth along (002) plane. The average opticaltransmittance of MAZO/AZO composite films in the visible region was still over90%,however, the visible emission in the visible region in the photoluminescence spectrawas obviously inhibited, and the ultraviolet emission was promoted.(4) Mg doped ZnO (MgZnO) thin films were prepared on quartz glass viamodified Pechini method. XRD results showed that MgZnO with Mg dopingconcentration under10%possessed hexagonal wurtzite structure, and (002)diffraction peak shifted to high angle with increase in Mg doping concentration. Theaverage optical transmittance of MgZnO thin films in the visible region was over90%.The optical band gap of MgZnO thin films increased from3.36eV to3.66eV withincreasing Mg doping content. The room temperature photoluminescence spectrashowed that the green emission was red-shifted from522nm to550nm, and theintensity of green emission gradually increased, when Mg doping concentrationincreased from3%to10%.