Sublimation Growth and Defect Characterization of AlN Single Crystals
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1040-Q03-01
Sublimation Growth and Defect Characterization of AlN Single Crystals Shaoping Wang1, Balaji Raghothamachar2, Michael Dudley2, Zaiyuan Ren3, Jung Han3, and Andrew G. Timmerman1 1 Fairfield Crystal Technology, LLC, 8 South End Plaza, New Milford, CT, 06776 2 Department of Materials Science & Engineering, State University of New York at Stony Brook, Stony Brook, NY, 11794 3 Department of Electrical Engineering, Yale University, 15 Prospect Street, New Haven, CT 06520
ABSTRACT In this paper, we report results from AlN single crystal growth experiments using a sublimation physical vapor transport growth technique. AlN single crystal boules up to 7mm in diameter were demonstrated. Characterization of polished AlN single crystal samples was carried out using various techniques, including synchrotron X-ray topography. INTRODUCTION AlN single crystal is a promising substrate material for high quality III-V nitride epitaxy, especially for fabrication of short wavelength (UV and blue) III-nitride-based devices employing high Al concentrations (e.g. 30% Al). AlN has the same crystal structure as GaN, AlxGa1-xN epitaxial layers lattice match all crystal planes of AlN, which cannot be easily done with either sapphire or SiC. Since AlN also has a high thermal conductivity, III-nitride-based devices fabricated on AlN substrates will be better able to dissipate heat. This will contribute significantly to better efficiency, longer lifetime and lower degradation. AlN single crystals can be grown using physical vapor transport (PVT) techniques, based on the pioneering work done by Slack and McNelly [1, 2]. In recent years, intense research efforts were made in developing AlN PVT bulk crystal growth techniques and AlN single crystals of more than 12mm in diameter were demonstrated [3]. However, more efforts are needed in order to achieve commercial volume production of high quality, large diameter (≥2inch) AlN single crystal substrates. In this paper, we report results from AlN single crystal growth experiments carried out at Fairfield Crystal Technology using a sublimation physical vapor transport (PVT) technique at high temperatures (>2100ºC). AlN single crystal boules up to 7mm in diameter were demonstrated and AlN boules with multiple crystal grains up to 26mm in diameter were produced. Characterization of AlN single crystal samples was carried out using various techniques, such as optical microscopy, AFM, thermal etching technique, X-ray double-crystal diffraction, and synchrotron X-ray topography. EXPERIMENTAL PROCEDURE AlN PVT growth experiments were carried out in a proprietary high-temperature PVT growth furnace. AlN source materials used in the growth experiments were pre-sintered at high temperatures (>2100ºC) to reduce the amount of oxygen and carbon in the original commercially available AlN fine powders. Crucibles used in the experiments were made of different refractory
metals, such as tungsten, tantalum, niobium, and their carbides or nitrides. The growth temperature was in the range of 2100-2300 ºC and
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