A Novel Growth Technique for Large Diameter AlN Single Crystal

Nitride-based, high-brightness, ultraviolet, visible, and white light emitting diodes are candidate devices for replacing incandescent light bulbs and fluorescent light fixtures in general illumination applications, due to their tremendous energy saving potential, long lifetime, and high efficiency. However, the poor crystalline quality of the nitride epilayers, resulting from severely lattice-mismatched and crystal-structure-differed substrates, prevents higher-light-output efficiency from being achieved. Native aluminum-nitride single crystal has been shown to have the same crystal structure and a close lattice match to group III-nitride epilayers, and it can be grown in bulk single crystal form. Therefore, this project will develop aluminum nitride substrates suitable for the growth of high quality nitride epitaxial layers, leading to the fabrication of high brightness light emitting diodes for general lighting applications. In Phase I, aluminum nitride crystal boules larger than 20mm in diameter were demonstrated by using a novel, sublimation, physical-vapor-transport growth technique, and aluminum nitride crystal wafers of about 20mm in diameter were fabricated. Phase II will continue to develop and improve the sublimation physical-vapor-transport technique so that single crystal aluminum nitride boules of 2-inch in diameter can be produced. Aluminum nitride wafers and epi-ready aluminum nitride substrates will be fabricated from the aluminum nitride crystal boules. To demonstrate the suitability of the aluminum nitride substrates for high quality nitride epitaxy, III-nitride epi-layers will be grown on aluminum nitride substrates, using a metal-organic chemical vapor deposition technique. Commercial Applications and other Benefits as described by the awardee: The aluminum nitride substrates should be suitable for volume production of high brightness light emitting diodes, with high-light-output efficacies adequate for general illumination applications. In addition, the high-quality aluminum-nitride substrates should find use in the fabrication of other types of nitride-based devices, such as blue laser diodes for optical recording, high frequency devices for telecommunications, and UV detectors for analytical applications (e.g., for the detection of chemical and biological agents for homeland security).