Electroluminescent Textiles using Sputter-deposited Amorphous Nitride-Rare-Earth Ion Coatings
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Electroluminescent Textiles using Sputter-deposited Amorphous Nitride-RareEarth Ion Coatings M.E. Kordesch, Department of Physics, Ohio University, Athens, OH 45701 Hugh H. Richardson, Department of Chemistry, Ohio University, Athens, OH 45701 Wide bandgap semiconductors have been sputter deposited onto non-crystalline substrates, low melting point materials, including polymer fibers, textiles and glasses. The semiconductors are amorphous and can be deposited over large (square meter) areas economically. The electro-optical properties of these materials are not defect limited, and do not require thermal processing. Alternating current electroluminescent device structures/coatings composed of rare-earth ion doped nitrides have been deposited onto point-bonded fabrics, polymer membranes, and polymer sheets. Light emission is detected from the coated fabrics over the entire visible range, UV and IR. A notable feature of fabric-based structures is the inclusion of ambient air in the fabric voids. Increased light emission intensity is obtained by extracting electrons from the plasma discharge during device operation. These fabrics do not require weaving, which could be difficult with semi-crystalline or brittle semiconductor materials. Multilayer assembly and bonding with continuous sheets, cladding, filling and or contact bonding are all available at any point in the fabric assembly. Non-woven, pin-bonded, materials may still function after some damage, e.g. rips or punctures, due to redundant connections at each pad. INTRODUCTION The successful incorporation of Rare Earth (RE) ions into nitride semiconductors for visible light emission was pioneered by Steckl [1-4]. Several reports of visible luminescence in amorphous nitride materials, deposited by reactive sputtering of metals in nitrogen at temperatures as low as 100 K [5-13], on many non-standard substrates, have suggested that these materials could be used for electroluminescent textiles. The deposition process is scalable and may be applied to the fibers or yarns before or after fabric formation. Further advantages are the simple incorporation of optically active ions, such as rare earths, high thermal conductivity, high breakdown voltage, and complete miscibility of the group III-A and -B nitrides, allowing bandgap engineering [14,15]. EXPERIMENTAL The nitride-rare earth coatings were deposited in a cryopumped vacuum chamber. Aluminum metal targets were used, 5-6 mm diameter metal “plugs” were inserted into the aluminum targets, so that the rare-earth metals were co-sputtered in pure nitrogen. Compositions by weight of up to 30 % rare earths could be mae, usual concentrations were from 1-5 %. Typical operation was 100-200 Watts rf power, at 5 m Torr nitrogen.
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The substrates were located about 100 mm from the sputter target, deposition rates and thickness were monitored by a quartz crystal thickness monitor. Typically a 150 nm thick film could be deposited in 60 minutes. Further details are in [5-13] RESULTS In reference [13], the authors showed
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