Light Emitting Diode Growth on Curved Gallium Nitride Surfaces
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Light Emitting Diode Growth on Curved Gallium Nitride Surfaces L. E. Rodak1, K. Lee1, V. Kumbham1, V. Narang2, L. A. Hornak1, and D. Korakakis1 1
Lane Department of Computer Science and Electrical Engineering, West Virginia University, PO Box 6109, Morgantown, WV 26506 U.S.A. 2 Department of Physics, West Virginia University, PO Box 6315, Morgantown, WV 26506 U.S.A. ABSTRACT III-Nitride based Light Emitting Diodes (LEDs) are heavily pursued for various lighting applications due to the ability to engineer the emission through the visible wavelengths by controlling the alloy composition in the multi quantum well. Planar structures are characterized by a Lambertian emission pattern, however, depending on the applications in which the LED is employed, including but not limited to, general lighting, displays, and sensors, the emission profile may need to be more or less directional. As a result, there is significant interest in both improving the efficiency and controlling the emission profile of nitride based devices. Various components such as lenses and photonic crystals are used to improve light extraction and alter the emission profile while growth on semi-polar substrates is being pursued to minimize inherent polarization effects. In this work, curved Gallium Nitride (GaN) structures have been grown utilizing growth kinetics. These as-grown features do not require the extensive additional fabrication and allow for three-dimensional substrates to be employed for LED fabrication. The details of the fabrication and the optical and electrical characterization of Indium Gallium Nitride based LEDs grown on these structures is discussed. INTRODUCTION III-Nitride based Light Emitting Diodes (LEDs) continue to attract attention due to the ability to engineer the emission across the visible spectrum1. Particular emphasis has been given to the fabrication of high efficiency blue and green LEDs as the III-Nitride system is the only material family that can cover this range. Applications include, but are not limited to, solid state lighting, full color displays, automotive lighting, and mobile device lighting2. Depending on the application, either narrow or broad radiation patterns are desirable. For example, in solid state lighting applications, broad patterns are used to create uniform lighting from most angles. However, for short distance fiber optic communications, narrow emission patterns are necessary to improve fiber coupling efficiency3. Despite commercial success, nitride based LEDs are still hindered by limited efficiency. Part of this inefficiency arises from limited light extraction as nitride based devices have a narrow light escape cone and part from limited internal quantum efficiency due to material defects and polarization effects2. As a result, considerable research efforts have focused on developing techniques to modify the emission pattern and improving the efficiency of nitride based LEDs including, but not limited to, micro-lens4,5, photonic crystals2,6, resonant cavity devices3, and three-dimensional fac
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