The Durability of Various Crucible Materials for Aluminum Nitride Crystal Growth by Sublimation
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Internet Journal Nitride Semiconductor Research
The Durability of Various Crucible Materials for Aluminum Nitride Crystal Growth by Sublimation B. Liu1, J.H. Edgar1, Z. Gu1, D. Zhuang1, B. Raghothamachar2, M. Dudley2, A. Sarua3, Martin Kuball 3 and H. M. Meyer III4 1Department
of Chemical Engineering, Kansas State University, of Materials Science Engineering, State University of New York at Stony Brook, 3University of Bristol, H. H. Wills Physics Laboratory, 4Oak Ridge National Laboratory, High Temperature Materials Laboratory, 2Department
(Received Monday, July 12, 2004; accepted Wednesday, October 20, 2004)
Producing high purity aluminum nitride crystals by the sublimation-recondensation technique is difficult due to the inherently reactive crystal growth environment, normally at temperature in excess of 2100 °C. The durability of the furnace fixture materials (crucibles, retorts, etc.) at such a high temperature remains a critical problem. In the present study, the suitability of several refractory materials for AlN crystal growth is investigated, including tantalum carbide, niobium carbide, tungsten, graphite, and hot-pressed boron nitride. The thermal and chemical properties and performance of these materials in inert gas, as well as under AlN crystal growth conditions are discussed. TaC and NbC are the most stable crucible materials with very low elemental vapor pressures in the crystal growth system. Compared with refractory material coated graphite crucibles, HPBN crucible is better for AlN self-seeded growth, as crystals tend to nucleate in thin colorless platelets with low dislocation density.
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Introduction
Aluminum nitride (AlN) is one of the most promising substrates for next generation high power, high frequency, and short wavelength optoelectronic devices based on gallium nitride (GaN) and its alloys [1]. Its extraordinary physical, chemical, optical, and electrical properties make it attractive in III-nitride epitaxial film applications, as addressed elsewhere [2]. The benefits of AlN compared to sapphire or silicon carbide as a substrate for GaN-based devices include a reduced lattice constant mismatch hence lower defect densities and a reduced coefficient of thermal expansion mismatch thus lower thermal stress. Because the structure of AlN is identical to GaN, epitaxial films can be grown on all crystal orientations, not just the (0001) plane. This may eliminate polarization effects and improve the quantum efficiency of nitride semiconductor LEDs and laser diodes. AlN will not alter the charge carrier background concentration in eptiaxial films by diffusion or autodoping as it is composed of only group III and group V elements that are isoelectronic with GaN. The properties of AlN even more closely match those of high Al mole fraction AlGaN epitaxial layers, which are necessary for
the fabrication of deep ultraviolet (DUV) optoelectronic devices [3] [4]. The initial reports on transistors and LEDs using AlN substrates demonstrate its promising characteristics [5] [6]. In short, using AlN s
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