Abstract
Nanostructured undoped zinc oxide (ZnO) thin films were deposited using atmospheric pressure chemical vapor deposition (APCVD) on glass substrates using zinc acetate dehydrate [C4H6O4Zn·2H2O, ZnAc] in less than 2 minutes for each sample. In order to reduce the resistivity of ZnO films, a very thin layer of Ag was deposited on top of the films via the sputtering method to reduce resistivity from 2.89 to 0.31 Ω.cm, using only a 30Å silver coating. Structural, electrical and optical properties of the resulting bilayers were also investigated. The results show a polycrystalline structure in higher temperatures compared to rather amorphous ones in lower temperatures such as 325℃. The XRD patterns of the optimum polycrystalline films were identified as a hexagonal wurtzite structure of ZnO with the (002) preferred orientation. Also, sheet resistance decreased from 17.8 MΩ/⧠ to 28.9 KΩ/⧠ for the temperatures of 325℃ to 450℃, respectively. Based on the physical properties of undoped ZnO, substrate temperature is an important factor which affects the crystallite size and modifies electrical parameters. UV-vis measurements revealed a reduction in the transparency of the layers with increasing substrate temperature. A sharp cut-off was observed in ultraviolet regions at around 380 nm.
Highlights
Zinc oxide (ZnO) is a wide-band-gap (3.37 eV) semiconductor with a large (60 meV) exciton binding energy
ZnO is fabricated by various methods such as sputtering 8, spray pyrolysis, 9-13 sol-gel 14, thermal oxidation 15, pulsed laser deposition (PLD), 16,17 thermal evaporation 18, spin coating 19, chemical vapor deposition (CVD) . 20-22 ZnO can exist in one, two, or three dimensional structures, giving one of the most considerable collections of diverse particle structures in all materials 23
The zinc acetate dihydrate powder vapor entered the substrate at the atmospheric pressure, and undoped ZnO films were deposited on the substrate
Summary
Zinc oxide (ZnO) is a wide-band-gap (3.37 eV) semiconductor with a large (60 meV) exciton binding energy. The CVD of films and coatings contains the chemical reactions of reactants in a gaseous phase on or in close vicinity of an already heated substrate surface. This atomistic deposition process can provide highly pure materials with a good structural control at a nanometer or atomic scale level 27. Atmospheric CVD is advanced by the production of active precursor vapors via gas-phase reactions They diffuse through a thin hydrodynamic boundary film above the substrate. Because of the low reactivity of oxygen or metal precursors, temperatures above 300°C for the substrate are needed for surface reactions, activating the gas-phase, and having high rates of film growth 30
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