Optical, electrical and structural properties of sol gel ZnO:Al coatings

• Published in: Thin solid films 1999-08, Vol.351 (1-2), p.125-131
• Main Authors: SCHULER, T, AEGERTER, M. A
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport phenomena in thin films and low-dimensional structures; Exact sciences and technology; Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids); Low-dimensional structures (superlattices, quantum well structures, multilayers): structure, and nonelectronic properties; Low-field transport and mobility; piezoresistance; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Physics; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties)
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/S0040-6090(99)00211-4

Single and multilayer transparent conducting aluminium doped zinc oxide films have been prepared on DESAG AF45 substrates by the sol gel dip coating process. Zinc acetate solutions of 0.1-0.5 M in isopropanol stabilised by diethanolamine and doped with a concentrated solution of aluminium nitrate in ethanol were used. Each layer was fired at 600 degree C in a conventional furnace for 15 min. The final coatings were then tempered under a flux of forming gas (N sub(2)/H sub(2)) at 400 degree C for 2 h. The coatings have been characterised by surface stylus profiling, optical spectroscopy (UV-NIR), X-ray diffraction (XRD), transmission electron microscopy (TEM) and combined Hall and van der Pauw techniques. Single layers with thickness, d, ranging from 25 to 186 nm are polycrystalline with the zincite structure and exhibit a small preferential orientation with the (002) direction perpendicular to the surface (texture coefficient, TC, ranging from 1.8 to 2.8). They consist of almost spherical particles with size ranging from 15 to 25 nm (thin sample) to 40 nm (thick sample) with crystallite sizes ranging from 23 to 40 nm (002), respectively. The film resistivity decreases from 5 x 10 super(-1) Omega cm (d identical with 25 nm) to 4 x 10 super(-2) Omega cm (d identical with 186 nm). Multilayer coatings built with about 20 nm thick layers are also slightly textured along the (002) direction (TC ranging from 1.9 to 2.8). A structural evolution in morphology from spherical to columnar growth was observed. The crystallite size calculated from the (002) reflex increases with the number of layers from 23 nm for a single layer to over 100 nm for ten layers. The resistivity decreases from 5 x 10 super(-1) Omega cm for a single layer to 5 x 10 super(-3) Omega cm for ten layers (d identical with 174 nm). A model for the growth of the crystallites in sol gel multilayer coatings is presented.