Rearch On Growth Preferential Orientation And Physical Properties Of Znic Oxide Thin Films Prepared By Chemical Bath Deposition

Zinc oxide (ZnO) is a II-VI metal oxide semiconductor, and has been regarded as third generation semiconductor material due to its relatively wide direct band gap (-3.37 eV) and a large exciton binding energy (60 meV), which provides it a high potential for light emission at room temperature. In recent decades, the research of potential applications in the nanotechnology industry of ZnO is very active, such as optoelectronic devices, light emitting diodes, photodetectors, gas sensors and so on. In addition, cheap and abundant raw materials, good biocompatibility, non-toxic, good chemical and thermal stability and strong radio resistance ability have made ZnO a material of choice for future applications.At present, researches on ZnO thin films with growth preferential orientation focuses on physical methods, such as molecular beam epitaxy, RF magnetron sputtering, pulsed laser deposition, etc., but expensive equipment, high cost, complex operation and high vacuum restrict these methods developing. In this paper, choosing cheap and high optical transmittance amorphous glasses as substrates, using a simplicity of operator and reaction easy to control method chemical bath deposition prepares growth preferred orientation of ZnO thin films, but growth directly on the bare amorphous glass is fairly difficult, therefore, ZnO seed layer is prepared in advance on the amorphous glass by Sol-Gel, which gives the chemical bath deposition process of ZnO deposition provides nucleation points, reduces the nuclear power, succeeding in solving this problem, and also because there is no strict epitaxial relationship between the film and the substrate, and does not produce residual stresses caused by atomic mismatch. In addition, ZnO seed layer and chemical bath deposition ZnO thin film are the same materials, so the thermal expansion coefficients are also quite close, successfully avoiding the strain caused by temperature change. The key parameters during the preparation of ZnO seed layer have been studied, such as sintering temperature, the precursor solution MEA/Zn2+ratio, spin-coating times, aging temperature, kind of solvent, etc. Researches on process of the parameter indicate that, when the sintering temperature is on the range of 370-500?, sintering temperature has little effect on the orientation of ZnO films prepared by chemical bath deposition, but impacts its grain size, when sintering temperature is 370?, the grain size is slightly larger than 400? and 450?. when sintering temperature range 400? to500?, the grain size increased gradually, but when the temperature is higher than 500?, due to the reaction of ZnO seed layer and SiO2 in amorphous glass, reducing the ZnO seed layer and undermining the continuity of the seed layer film, so ZnO thin films by chemical bath deposition are not fairly continuous. MEA has a strong protonated ability and complex with Zn2+to be dispersed in the sol to form a uniform system of Zn2+, and at the same time MEA ensure the stability of sol. MEA/Zn2+ratio of precursor solution affects the quality of ZnO thin films, when MEA/Zn2+=0.5, the complexation is relatively weak and the dispersion of system is not good, and when MEA/Zn2+=2.5, there are many macroscopic defects in the ZnO thin films ater chemical bath deposition as a result of the generation of aggregates. The times of the spin-coating mainly impact ZnO (002) orientation, with the spin-coating times increasing, (002) diffraction peak relative intensity was significantly enhanced. The aging temperature and solvent species seriously affect the preferred orientation of the final films, and found that when the aging temperature is 18?, the non-polar preferred orientation and quality of the final film is the best.During the process of chemical bath deposition, the research mainly focus on the influence of the kind and content of alcohol and non-polar auxiliary agent. Different alcohols have different properties, adsorbing on a certain ZnO plane, inhibiting the growth. As a result, methanol may be adsorbed on (110), (100) and (002) ZnO plan, and ethanol, isopropanol and n-propanol may be adsorbed on (002) and (101) crystal plane, which is more conducive to ZnO (100) and (110) plane direction of growth. non-polar auxiliary agent Mainly adjusts the polarity of solution. Like the "like dissolves like" principle, when the polarity of the solution is similar with that of a certain of ZnO crystal plane, the crystal plane will grow faster; Different non-polar auxiliary agent have its own range of concentration for preparation of non-polar ZnO thin films. When the concentration increases, with the generation of the non-polar films, the non-polar solution will be aggregated on the ZnO non-polar plane, hindering Zn2+moving to the substrate surface, resulting in a film thickness decreases. When the concentration is too high, even only a small amount of thin film forms.This article also investigated crystal structure and surface morphology of different preferred orientation ZnO thin films by XRD, AFM and SEM and found that (100) preferred orientation and (100) and (110) preferred orientation has a similar morphology, surface roughness of (110) preferred orientation thin film is the largest, and surface roughness of (101) preferred orientation thin film is minimized. Also, the surface wettability was studied, (110) preferred orientation thin film has good hydrophobicity, however, followed by hydrophobicity of (101) preferred orientation thin film. The hydrophobicity of (100) preferred orientation and (100) and (110) preferred orientation thin films is poor. Photoluminescence spectra and UV-visible spectroscopy indicate that the crystalline thin films having a good quality and high transmittance.