The effect of substrate-induced strain on the structural, electrical and optical properties of polycrystalline ZnO thin films was studied using x-ray diffraction, scanning electron microscopy, electrical resistivity and photoluminescence measurements. The orientation, crystallite size, and electrical resistivity were found to depend strongly upon the substrate induced strain along the c axis. A relatively large tensile strain was shown to exist in ZnO deposited on sapphire and glass, while a smaller compressive strain was found in film deposited on GaN. The results show that GaN, being a closely lattice matched substrate, produces ZnO films of better crystallinity with lower resistivity.
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