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Synthesis and Characterization of ZnO Films by Ultrasonic Spray Pyrolysis

Author: ZhongAiHua
Tutor: TanJin
School: China University of Geosciences
Course: Materials Science and Engineering
Keywords: Ultrasonic spray pyrolysis ZnO thin films Glass substrate Transparent conductive film Doping
CLC: TB43
Type: Master's thesis
Year: 2011
Downloads: 76
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Abstract

ZnO is a very important function direct band-gap-type wide band gap semiconductor material. The band gap of 3.37 eV, the exciton binding energy up to 60 meV. High exciton binding energy so that the excitons can exist stably at room temperature, so in theory the material has a high luminous efficiency. Further, since the ZnO also has a high chemical stability, high visible light transmittance, a low preparation temperature, environment-friendly and cheap raw materials easily obtained and other characteristics such that in the solar cell, a flat display, in particular a light emitting diode (LED) and laser diode (LD) has great application prospects. Present ZnO study focused on three areas: ZnO nanostructures, ZnO transparent conductive film, as well as the development of p-type ZnO. In these studies direction, Development of the p-type ZnO is the most important, but also the most difficulty. Its importance is because once developed the performance of the p-type ZnO ZnO can be used to prepare optoelectronic devices such as light-emitting diodes and laser diodes, to bring about revolutionary changes to these areas. N elements is considered to be the most effective in the preparation of the p-type ZnO acceptor doping. Ideal doping N elements into the lattice, occupy O's grid points, and the formation of acceptor doping No.. However, the very low solid solubility of N elements in ZnO, even often not enough to offset their own self-compensation effect. Thus, the N-Al (including In, Ga) of doping technique is applied to the preparation of the p-type ZnO, and to improve the degree of solid solution of N and reduced by the main No dopant activation energy. In this thesis, using ultrasonic spray pyrolysis, N-Al co-doped ZnO films were prepared on a glass substrate and the single crystal silicon substrate. The substrate temperature, substrate type doped ZnO thin film structure and optoelectronic properties of Al concentration and film thickness. The systematic study of this thesis, a substrate temperature of ZnO thin films prepared substrate temperature were 300 ° C, 350 ° C, 400 ° C and 450 ° C. The study showed that the ZnO hexagonal wurtzite type ZnO. As the substrate temperature increases, the (002) crystal face should FWHM of the diffraction peak is gradually reduced, reflecting the ZnO grains and gradually increases with increasing substrate temperature. The atomic force microscope surface morphology analysis showed that ZnO particles gradually increases with increasing substrate temperature, in good agreement with the XRD analysis results. Fluorescence spectrometer test room temperature photoluminescence properties of the series of samples. The test results show that the low temperature deposition of samples have strong caused by the donor defects Zni and Vo, respectively, the blue band and green light emission band. With the substrate temperature of these donor defects emission intensity gradually weakened, and the spectrum was not observed when the substrate temperature of 450 ° C these defects emission, means that the temperature is under the ZnO film having a very low concentration of a donor defects . This can significantly reduce the self-compensating effect of the ZnO, and the preparation of the film of the p-type is very advantageous. Due to the lower melting point of ordinary silicate glass, the substrate temperature is further improved easily lead glass melting, and therefore determined 450 ℃ preferred substrate temperature. In single crystal silicon (100) substrates by a series of different concentration of Al-doped N-Al co-doped ZnO films. Its emission spectrum only in the near-UV emission peak near 382 nm. The film luminous intensity gradually increased with increasing Al doping concentration. The gradual increase of the UV luminescence is likely to be because, AlZn-No donor - acceptor concentration increases, resulting in N-Al co-doped ZnO films electron - hole concentration increases with increasing Al doping concentration, so that the electron - hole recombination luminescence enhancement. The results of the study can be used to improve the emission intensity of the ultraviolet light emitting device. In order to study changes in the structure of the different growth stages of ZnO thin films and photovoltaic performance, which provide a reference for the choice of the film thickness, the paper system study of film thickness on the N-Al co-doped ZnO thin films prepared. The thickness of the film was 80 nm, 235 nm, 545 nm, 700nm and 1440nm. XRD results show that, as the film thickness increases, the (002) diffraction peak gradually weakened ZnO particle size gradually increases; surface morphology analysis showed that the ZnO particles gradually grow its morphology from the rules of the hexagonal nano-flakes into a wedge-shaped, conical; redshift of light-induced luminescence center wavelength with increasing film thickness from the near-UV band of red to the blue band. Combined with the experimental results and previous reports the analysis of the emitted light in the blue-violet wavelengths defect concentration is gradually increased, leading to the luminous center moves toward the long-wavelength, which happened redshift With the increase in the film thickness film. The defects are likely the related defects Zni. Therefore, the thin film thickness of less than 300 nm, the donor defect concentration is small, there are conducive to the preparation of the film of the p-type. Finally, the papers were prepared ZnO: Al transparent conductive film. Adjustment before the precursor solution, the minimum surface resistivity only reached 4.1 F2 · cm or average visible transmittance of 85% -90%, its conductivity is significantly poorer performance; by adjusting the precursor component, on a glass substrate preparation of a transparent conductive thin film resistivity can be as low as 1.93 × 10-2Ω · cm, the resistivity after annealing further decreased to 3 × 10-3Ω · cm, while the visible light transmittance is increased to 93.97%. It is understood that the experimental results prepared by spray pyrolysis ZnO: In transparent conductive film reached world leading level. Compared with a widely used magnetron sputtering method using a transparent conductive film prepared by spray pyrolysis obviously has a high visible light transmittance and the surface resistivity is only slightly lower than magnetron sputtering. By further optimization, will have a very high industrial application value.

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