Growth of AlN Crystals

"The objective of this proposal is the fabrication of AlN substrates with single crystalline quality meeting or exceeding the standards of commercially available SiC wafers. The growth process, which utilizes high temperature, subatmospheric pressure, and asteep temperature gradient, yields high-purity AlN single crystals at commercially interesting growth rates by sublimation of AlN in a nitrogen atmosphere. Through the proposed research, HexaTech, Inc. plans to increase the size of AlN bulk crystals,targeting the demonstration of 2" boule diameter, without compromising the crystal quality. Wafering and polishing will be performed at NCSU. The properties of grown crystals will be evaluated at NCSU and will include (1) microstructural analyses (opticaland scanning electron microscopies, x-ray diffraction, Raman spectroscopy), (2) chemical analysis (X-ray photoelectron spectroscopy), (3) identification of impurities (secondary ion mass spectroscopy, optical techniques), and (4) study of electricalproperties (I-V, Hall measurements). AlN wafers will find an immediate application as lattice-matched substrates for high-quality epitaxy of III-nitrides and will enable the fabrication of superior quality AlGaN electronic and optoelectronic devices,including high-frequency amplifiers and switches, blue and UV solid state lasers, solar-blind UV detectors, and surface acoustic wave (SAW) devices. Since the epitaxial processes and a variety of III-nitride device structures have been developed during thepast ten years on less favorable substrates with large lattice mismatch, the penetration of these new AlN wafers into the market place can occur without delay and to the immediate benefit of device performance."