Aluminum Nitride-Silicon Carbide Alloy Crystals Grown on SiC Substrates by Sublimation
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Internet Journal Nitride Semiconductor Research
Aluminum Nitride-Silicon Carbide Alloy Crystals Grown on SiC Substrates by Sublimation Z. Gu1, L. Du1, J.H. Edgar1, E.A. Payzant2, L. Walker2, R. Liu3 and M.H. Engelhard4 1Department
of Chemical Engineering, Kansas State University, Ridge National Laboratory, High Temperature Materials Laboratory, 3Department of Physics and Astronomy, Arizona State University, 4Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, 2Oak
(Received Monday, November 28, 2005; accepted Monday, December 19, 2005)
AlN-SiC alloy crystals, with a thickness greater than 500 µm, were grown on 4H- and 6H-SiC substrates from a mixture of AlN and SiC powders by the sublimation-recondensation method at 1860-1990 °C. On-axis SiC substrates produced a rough surface covered with hexagonal grains, while 6H- and 4H- off-axis SiC substrates with different miscut angles (8° or 3.68°) formed a relatively smooth surface with terraces and steps. The substrate misorientation ensured that the AlNSiC alloy crystals grew two dimensionally as identified by scanning electron microscopy (SEM). Xray diffraction (XRD) and transmission electron microscopy (TEM) confirmed that the AlN-SiC alloys had the wurtzite structure. Electron probe microanalysis (EPMA) and x-ray photoelectron spectroscopy (XPS) demonstrated that the resultant alloy crystals had non-stoichiometric ratios of Al:N and Si:C and a uniform composition throughout the alloy crystal from the interface to the surface. The composition ratio of Al:Si of the alloy crystals changed with the growth temperature, and differed from the original source composition, which was consistent with the results predicted by thermodynamic calculation of the solid-vapor distribution of each element. XPS detected the bonding between Si-C, Si-N, Si-O for the Si 2p spectra. The dislocation density decreased with the growth, which was lower than 106 cm-2 at the alloy surface, more than two orders of magnitude lower compared to regions close to the crystal/substrate interface, as determined by TEM.
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Introduction
Aluminum nitride-silicon carbide alloys can be prepared with a wide range of physical and electronic properties that are superior to the pure binary components. This is an excellent system for bandgap engineering, as its band gap changes from 6.2 eV (for AlN) down to 2.9 eV (for 6H-SiC), and potentially 2.3 eV if the cubic structure 3C-SiC can be stabilized. The band transition changes from indirect for SiC-rich to direct for AlN-rich alloys (>70 %). Both n and p type conductivities have been reported. AlN-SiC alloys retain the best properties of the pure binary compounds: high electron break down field, high saturated electron drift velocity, and high thermal conductivity [1] [2] [3] [4] [5] [6] [7] [8]. Much research has already been carried out on the preparation and characterization of AlN-SiC alloy crystals. Both thin films and bulk crystals of AlN-SiC alloys have been prepared over the entire compositional range.
Solid solutions
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