Al-doped and undoped zinc oxide films obtained by soft chemistry

Zinc oxide with a hexagonal wurzite type structure is an unique material that exhibits semiconducting, piezo- electric and pyroelectric properties. These properties play a key role for applications in optoelectronic devices. In the present work Al-doped and undoped ZnO fi lms were obtained by soft chemistry starting with zinc acetate dihydrate and Al(III) isopropoxide in absolute ethyl alcohol. Trietanolamine was used as chelating agent. The fi lms were deposited by dip coating technique on the silicon substrate and thermally treated at 500°C for one hour. The morphological characteristics of the fi lms were investigated by Atomic Force Microscopy (AFM). Optical constants, such as refractive index (n) and extinction coeffi cient (k), were established by Spec- troellipsometry measurements. Electrical conductivity of the studied fi lms was determined in the 20-500°C temperature range by "the four point method". The morphology of the fi lms is infl uenced by the starting sol composition, as found from AFM. According to the ellipsometric spectral data, more porous and thinner fi lms, with smaller refractive index were obtained in the case of Al-doped ZnO fi lms as compared with ZnO fi lms. Both ZnO and Al-doped ZnO fi lms presented high electrical resistivity.