Research On Optical And Electrical Properties Of Al Doped ZnO Thin Films Prepared By Sol-Gel Method

Zinc oxide is a direct wide band gap II-VI group compound semiconducting material. At room temperature, the band gap of Zinc oxide is about 3.37 eV, which leads to a very high transmittance within the visible light wavelength. Besides, aluminum dopant can improve its conductance effectively. Because of these excellent characters, Aluminum doped ZnO (AZO) thin films would be applied as a kind of Transparency Conductive Oxidate (TCO) Films, which can replace the widely used Tin doped Indium Oxide (ITO) thin films.Internal and international research progresses in AZO thin films and some basic theories of ZnO were reviewed in this paper. Considered all the methods of preparing thin films presently been used, a circumstance friendly and convenient to produce in business method, Sol-Gel dip-coating, was adopted and researched.In this paper, the chemical reaction theories during the Sol-Gel preparing process have been raised. Based on these conclusions, by adding monoethanolamine (MEA) into the solution, the -NH2 could make bond with Zn2+, then one kind of ligand was achieved, so MEA was used as a chelator. Besides, the transition from Sol to Gel occurred during the period of drying process when the wet films were exposed in the air. At that time, the wet films adsorbed the water in the air, which could offer an element of hydrolysis and dehydration polycondensation. Due to this point, the wet films after each dip-coating should be hanged and exposed in the air for several minutes, experiments had proved that it could improve the properties of the thin films.The film properties were characterized by X-ray Diffractometer, Differential Thermal Analysis, Field Emission Scanning Electronic Microscopic, Ultraviolet-visible Spectrophotometer, Fluorescence Spectrophotometer and Four-probe tester. Based on the results of characterization, influences of technical parameters on film formation were studied. Sol content, dopant concentration, preheating temperature (Tpre) and annealing temperature (Tanneal) were strong correlation factors when prepared the films. In the condition that [Zn2+]=0.6 mol/L, Al/Zn2+=1.5 at.%, Tpre=300°C, Tanneal=550°C, films with best quality could be prepared.The test data also revealed that there were obvious quantum effects, such as Burstein-Moss, Stokes and the band gap narrowed after annealing etc. The theoretical explanations for these effects were given in the paper.The AZO transparency conductive thin film prepared in our experiments had high transmittance. However, the conductance was not good enough, which was elevated obviously after been annealed in the N2 atmosphere.