The objective of this proposal is to demonstrate the feasibility of growing centimeter-size aluminum nitride (AlN) crystals by subliming polycrystalline AlN in nitrogen atmosphere, and to demonstrate single crystalline quality meeting or exceeding the standards of commercially available SiC wafers. The growth process, which utilizes high temperature, subatmospheric pressure and a steep temperature gradient, promises to yield high-purity AlN crystals at commercially interesting growth rates. The growth of small AlN crystals has recently been demonstrated at North Carolina State University (NCSU). Through the proposed research, Hexatech, Inc. plans to increase the size of AlN bulk crystals into the centimeter range, without compromising crystal quality. The properties of grown crystals will be evaluated at NCSU and will include (1) microstructural analyses (optical and scanning electron microscopies, x-ray diffraction, Raman spectroscopy), (2) chemical analysis (X-ray photoelectron spectroscopy), (3) identification of impurities (secondary ion mass spectroscopy, photoluminescence, optical absorption), and (4) study of electrical properties (I-V, Hall measurements).AlN wafers that eventually will be fabricated from the grown crystals 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 the past 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.
