High Mobility IGZO/ITO Double-layered Transparent Composite Electrode: A Thermal Stability Study
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High Mobility IGZO/ITO Double-layered Transparent Composite Electrode: A The rmal Stability Study Aritra Dhar1 and T. L. Alford1,2 1
Department of Chemistry and Biochemistry,
2
School for Engineering of Matter, Transport, and Energy,
Arizona State University, AZ 85287, U.S.A.
ABSTRACT The fabrication of a thin film optoelectronic device involves the exposure of the transparent conductive oxide (TCO) to a high process temperature. Indium gallium zinc oxide (InGaZnO4 or IGZO) is a well known TCO with high optical transparency, moderate conductivity and high mobility. However, its electrical properties deteriorate after subsequent high temperature processes in air atmosphere. On the other hand indium tin oxide (ITO) has higher conductivity than IGZO and better thermal stability. Therefore, IGZO/ITO bilayers have been deposited on glass by radio frequency magnetron sputtering at room temperature and subsequently annealed at high temperatures in order to study their thermal stability. In the present work, a-IGZO layers with a thickness ranging from 10 nm to 100 nm were deposited over a 50 nm thick ITO layer. Results are compared with those from a single IGZO layered thin film without the ITO bottom layer. The structural, optical and electrical properties of the multilayers are studied with the use of scanning electron microscopy, UV–Vis spectroscopy and Hall measurement. An IGZO optimal thickness of 50 nm is found to improve the bilayer thermal stability at temperatures upto 400 °C keeping good opto-electrical properties. The sheet resistance for the optimized IGZO/ITO composite films is about 22 Ohm/sq, and the transmittance in the visible range is about 90%. The composite shows an excellent mobility above 40 cm2 /V-s and thus can be potentially applied as channel layer in thin film transistors (TFTs) INTRODUCTION Transparent conducting oxides (TCO) have been widely used for various optoelectronic applications such as solar cells, [1] flat panel displays [2], gas sensors [3] and organic light emitting diodes [4]. TCO thin films are critical for solar cell devices since they constitute a essential part in the future generations of photovoltaic (PV) devices [5]. The most important criteria for a TCO is to have high visible transparency and good electric conductivit y. Also, low cost abundance, non toxicity, and simple fabrication methods at an industrial scale are other important characteristics to be considered for the selection of a TCO electrode for photovoltaic applications [6-10]. However, apart from these conventional characteristics, processing of PV devices requires high thermal and chemical stability, surface electrochemical properties and room temperature fabrication. For this reason, the research for new materials or various composites had been extensively studied to improve the performance and efficiency of the TCO
thin films. ITO is the most common and widely used TCO which has good properties in terms of high transparency and conductivity[8-13]. The advantage of ITO is that it can be easily fabricated
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