Electronic and optical properties in ZnO:Ga thin films induced by substrate stress |
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| Affiliation: | 1. Department of Physics and Energy Harvest–Storage Research Center, University of Ulsan, Ulsan 680-749, South Korea;2. Semiconductor Applications, Ulsan College, Ulsan 680-749, South Korea;1. Max Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle, Germany;2. University of Architecture, Civil Engineering and Geodesy, Faculty of Hydrotechnics, Department of Physics, 1, Hristo Smirnenski Blvd., 1046 Sofia, Bulgaria;3. University of Forestry, Faculty of Forest Industry, 10, Kl. Ohridsky Blvd., 1756 Sofia, Bulgaria;4. Institute of Physics, Martin-Luther-University, D-06099 Halle, Germany;5. University of Sofia, Department of Physics, Blvd. J. Bouchier 5, 1164 Sofia, Bulgaria;1. Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, People''s Republic of China;2. University of Science and Technology of China, Hefei 230026, People''s Republic of China;3. High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031, People''s Republic of China;4. Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, People''s Republic of China;1. Department of Physics, University of the Western Cape, Private Bag x 17, Bellville 7535, South Africa;2. DST/CSIR National Centre for Nano-Structured Materials, Council for Scientific and Industrial Research, Pretoria 0001, South Africa;3. Transnet Engineering, Product Development, Private Bag X 528, Silverton 0127, South Africa |
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| Abstract: | The effects of biaxial stress in ZnO:Ga thin films on different substrates, e.g., sapphire(0001), quartz, Si(001), and glass have been investigated by X-ray diffraction, atomic force microscopy, and electrical transport and ellipsometric measurements. A strong dependence of orientation, crystallite size, transport, and electronic properties upon the substrate-induced stress has been found. The structural properties indicate that a tensile stress exists in epitaxial ZnO:Ga films grown on sapphire, Si, and quartz, while a compressive stress appears in films grown on glass. The resistivity of the films decreased with increasing biaxial stress, which is inversely proportional to the product of the carrier concentration and Hall mobility. The refractive index n was found to decrease with increasing biaxial stress, while the optical band gap E0 increased with stress. These behaviors are attributed to lattice contraction and the increase in the carrier concentration that is induced by the stress. Our experimental data suggest that the mechanism of substrate-induced stress is important for understanding the properties of ZnO:Ga thin films and for the fabrication of devices which use these materials. |
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| Keywords: | Thin films Plasma deposition X-ray diffraction Electrical properties Optical properties |
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