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Wafer Bonding of Silicon Carbide and Gallium Nitride Jaeseob Lee, T. E. Cook, E. N. Bryan1, J. D. Hartman, R. F. Davis, and R. J. Nemanich1, 2 Department of Material Science & Engineering and Department of Physics1 North Carolina State University, Raleigh, NC 27695 2 E-mail address: [email protected] ABSTRACT Wafer bonding of SiC and GaN may prove important in the formation of high power heterojunction devices. Results of bonding SiC (C or Si surface) onto GaN (Ga surface) are presented. The samples were n-type 6H SiC and epitaxial n-type 2H(wurzite) GaN grown on SiC. The results demonstrate bonding for both possibilities, but the bonding of the C surface SiC to Ga surface GaN is more readily accomplished. A lower resistance was found for the C-face SiC/Ga-face GaN. The results indicate that the polarity of the interface is important for bonding of these materials. INTRODUCTION Silicon carbide is considered for high power and high temperature semiconductor device operation because the material exhibits a wide bandgap (3.0 eV) and high thermal conductivity (5W/cmºC). The operation of silicon carbide bipolar junction transistors with an even larger bandgap emitter would display increased current gain due to improved emitter efficiency. The larger bandgap of the emitter would restrict the diffusion of holes from the base to the emitter, resulting in high electron injection efficiency into the base. Additionally, the increased bandgap of the emitter allows the base to be heavily doped, thereby decreasing the base resistance. Also, since SiC is an indirect bandgap material, free carriers exhibit longer lifetimes, compared to a direct bandgap material such as GaN. The increased lifetime yields a long diffusion length, and a high base transport factor. Furthermore, these devices have a short base width, which further enhances the transport factor, thereby increasing the current gain. Gallium nitride is a natural choice for a larger bandgap emitter for SiC. Gallium nitride not only has a higher bandgap, 3.4 eV, than SiC, it also has a high thermal conductivity, 1.3W/cmºC. With a lattice constant of 3.18Å for GaN and 3.08Å for SiC epitaxy is possible, but the lattice mismatch (~3.4%) can significantly limit the quality of the epitaxial film [1,2]. The poor wetting of GaN on 6H-SiC(0001) substrates impedes direct nucleation and frequently results in GaN films of poor crystallinity. The use of an AlN buffer layer has been demonstrated to be effective in improving the crystallinity as well as in reducing the defect density in the GaN films, but simultaneously inhibits carrier injection across the AlN/SiC interface due to the insulating nature of AlN and its high band gap [3]. Reports of the growth of GaN directly onto 6H-SiC(0001) have noted the observation of an amorphous interlayer or zincblende inclusions at or near the GaN/SiC interface. Epitaxial growth by conventional techniques, e.g., molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD), is affected by lattice mismatch strain. During MB