Nanostructured indium tin oxide for application in optoelectronic devices
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Nanostructured indium tin oxide for application in optoelectronic devices S. P. Fernando1, K. D. Harris2, N. J. Gerein1, and M. J. Brett1,2 1 Electrical and Computer Engineering, University of Alberta, 114 St - 89 Ave, Edmonton AB, T6G2E1, Canada 2 NRC National Institute for Nanotechnology, Edmonton AB, T6G2M9, Canada ABSTRACT Nanostructured thin films of indium tin oxide were grown using glancing angle deposition, a physical vapour deposition technique which enables the preparation of columnar thin films with various morphologies. Indium tin oxide films consisting of vertical posts were electrically characterized using a probing station to determine their electrical resistivity. The nanostructured films were found to exhibit resistivities approximately two orders of magnitude greater than that of a normally evaporated film. However, development of the measurement technique is ongoing, and several ideas for improvement are described. INTRODUCTION Indium tin oxide (ITO) is a transparent conductor material commonly used in optoelectronic devices such as flat panel displays [1][2][3]. In current applications, this material is used as a planar electrode which allows for the simultaneous conduction of current and passage of light into or out of the device. However, the use of nanostructured ITO electrodes holds promise for enhanced performance in certain applications such as sensing, due to dramatically increased surface area. Glancing angle deposition (GLAD) is a thin film fabrication technique that is well suited to creating such electrodes. In GLAD, a physical vapour deposition technique, substrates are tilted at extreme angles relative to the incoming vapour flux. This tilting, combined with low adatom mobility, results in self-shadowing as the film grows, producing a thin film composed of individual columns. GLAD also incorporates computer-controlled motion of the substrate during the film deposition, which allows for precise control over the columnar morphology. GLAD has been used to deposit helices, polygonal spirals, slanted posts, and zig-zag structures of a variety of materials [4][5]. Using advanced techniques, column morphology and spacing can be manipulated independently [6], and regular arrays of columns can be grown [7]. In this work, the use of GLAD to produce nanostructured ITO electrodes was investigated. Specifically, the electrical resistivity of vertical post ITO films was measured (through the thickness of the film) and compared to that of an unstructured (planar) film. EXPERIMENT Planar films Planar films of ITO were grown to establish a baseline for comparison as well as to verify the suitability of the deposition procedure. An important aspect of the chosen procedure was the post-deposition anneal, which was required to make the resulting film transparent. Excessive annealing has an adverse effect on film conductivity [8], however, so a proper choice of annealing time and temperature is important. A variety of annealing parameters were tested before settling on an annealing temperat
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