High Quality, Low Cost Continuous Poly-GaN Film on Si and Glass Substrates Produced by Spin Coating
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High Quality, Low Cost Continuous Poly-GaN Film on Si and Glass Substrates Produced by Spin Coating Huaqiang Wu1, Athanasios Bourlinos2, Emmanuel P. Giannelis2, Michael G. Spencer1 1 401 Phillips Hall, School of Electrical & Computer Engineering, Cornell University, Ithaca, NY 14853 2 Department of Materials Science and Engineering, Cornell University, Ithaca, NY 14853 ABSTRACT Polycrystalline GaN layers have been produced on generic substrates via spin coating. Based on X-ray diffraction and SEM analyses, the GaN particles appear to be highly oriented on the surface. Strong luminescence from these layers has been demonstrated by cathodoluminescence. The source material was high purity, high quality GaN powder produced in our laboratory. Methyl cellulose was successfully used to disaggregate GaN particles in the dispersion. The colloidal dispersions were spun onto different substrates: Si, sapphire and glass. The dispersant was removed by annealing the sample at 500oC. The layer thickness was controlled by varying the number of spin coatings. Applications for spindeposited GaN layers include the fields of light emitting devices and random lasers. INTRODUCTION Gallium Nitride (GaN) has received a great deal of attention due to its optoelectronic and electronic properties.1,2 GaN layers are typically deposited on sapphire, SiC, or AlN substrates by either molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD) or hydride vapor phase epitaxy (HVPE).3-5 Because of sizeable mismatches of the lattice constants and thermal expansion coefficients, GaN can only be grown on certain substrates with small sizes, e.g. 2-4 inch substrates. In the literature, there are no reports of a GaN layer grown on glass or plastic substrates using the aforementioned techniques. It is impossible to deposit a GaN layer on a one meter substrate or rollable substrates. The limitations imposed by the available growth techniques and substrates makes GaN layers very expensive to produce. For large area substrates, one suitable solution is to deposit the GaN layer via a spin coating or dip coating process. These techniques have minimal requirements on substrate selection and have been widely used for producing ceramic thin films. In this article, we report the fabrication of GaN layers produced by spin coating. Different substrates (Si, sapphire and glass), have been successfully used for GaN layer deposition. Although the layer produced this way is polycrystalline, this technique provides the essential advantages of extremely low cost and flexibility in the choice of substrate types and sizes. Our technique can also serve a method to make composite materials with GaN as the inorganic component. The GaN films produced in this way can be used to make light emitting devices and random lasers.6 The structure, morphology, and luminescence properties of these films on different substrates have been characterized and are reported here.
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EXPERIMENTAL PROCEDURE To produce a GaN layer by spin coating, it is important to
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