Changes of structural, optical and electrical properties of sol-gel derived ZnO films with their thickness

Zinc oxide (ZnO) films having thickness in the range from 15 nm to 208 nm have been fabricated by the sol-gel technique by varying number of sequentially deposited layers. The structural, optical and electrical properties of ZnO films were investigated as a function of film thickness. The crystallinity and degree of orientation of the ZnO films were closely related to the film thickness. The textures of the films improved only at an optimum thickness. At lower thicknesses, the roughness of the film became very large and led to the presence of possible voids having porous microstructure. The absorption in UV region depended strongly on sequential layers and increased with the increase of film thickness. Films thinner than ca. 60 nm exhibit morphology and behaviour different from thicker ones. A marked increase in resistivity for thinner films can predominantly be attributed to surface scattering and the decrease in carrier concentration.