Properties of ITO thin films rapid thermally annealed in different exposures of nitrogen gas
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Properties of ITO thin films rapid thermally annealed in different exposures of nitrogen gas E. R. Ollotu1 · J. S. Nyarige3 · N. R. Mlyuka2 · M. E. Samiji2 · M. Diale3 Received: 12 May 2020 / Accepted: 5 August 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Indium tin oxide (ITO) thin films were rapid thermal annealed (RTA) for 5 min at a temperature of 550 °C in different exposures of nitrogen gas. Effects of these exposures on the structural, morphological, electrical, and optical properties of these films were investigated using X-ray diffraction, atomic force microscopy and field emission-scanning electron microscopy, four-point probe and hall effect measurements, and ultraviolet–visible-near-infrared (UV–VIS–NIR) spectrophotometer, respectively. The un-exposed RTA ITO films maintained (400) plane preferential orientation similar to the un-annealed sample. However, this plane preferential orientation was reduced relative to (222) plane for exposed RTA sample. The grains and surface roughness parameters were reduced for exposed and enhanced for un-exposed RTA samples as compared to the un-annealed sample. Relatively higher electrical conductivity, average solar transmittance, and bandgap values were observed for ITO films annealed while exposed to nitrogen gas. The exposed RTA ITO films showed sheet resistance of 7.91 Ω sq−1, average solar transmittance of 83%, and bandgap of 3.93 eV. Findings from this study suggest that RTA exposure have the potential to control ITO thin films properties, hence, extending its potential applications.
1 Introduction Demands for energy materials that are readily available, low cost, and easy to process have led to the development of novel optoelectronics and solar cells materials [1–6]. Application of such materials on the commonly used electrodes for optoelectronic devices needs further research to achieve such devices best performance. Indium tin oxide (ITO) thin films being a transparent conductor with outstanding optical and electrical properties has been extensively studied as transparent electrodes for organic light-emitting devices, liquid crystal displays, and solar cells [7]. Its high bandgap (above 3.7 eV) and n-type degenerate doping make ITO highly transmit visible radiation and conduct electric current, respectively. This conductivity in ITO thin films emanates from charge carriers donated by Sn+4 doping into * E. R. Ollotu [email protected] 1
Physics Department, Mkwawa University College of Education, P.O. Box 2513, Iringa, Tanzania
2
Physics Department, University of Dar es Salaam, P.O. Box 35063, Dar es Salaam, Tanzania
3
Department of Physics, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa
In2 O3 lattice and doubly charged oxygen vacancies [8]. Besides, vacancy-like oxygen defects are reported to contribute charge carriers where Sn is considered inefficiently activated [7, 9]. Post-deposition annealing in different annealing atmosphere is carried out in such ITO films to efficiently ac
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