Abstract
Due to the properties of large mismatch and strong polarization, the epitaxial growth and defect control of GaN films and GaN-based heterostructures on various Si substrates still face a series of scientific and technical issues. In recent years, the epitaxial growth of GaN thick films and AlGaN/GaN heterostrucures on Si (111), Si (110) and Si (100) substrates have been investigated systematically in our group. The “large lattice mismatch stress control” technology has been developed for the GaN epitaxy on Si substrates, and the 8-µm-thick, continuous GaN epilayers with low dislocation density and AlGaN/GaN heterostructures with the 2DEG mobility of 2240 cm2/V.s on Si (111) substrates have been achieved. AlGaN/GaN heterostructures of high quality on Si (110) substrates have also been realized. The key problem of the two-domain structure of GaN on a Si (100) substrate, which is caused by the reconstruction of Si (100) surface, has been solved by the innovation development of the SiO2/graphene interlayer in MOCVD growth, and thus the epitaxial growth of single-crystalline GaN films on Si (100) substrates has been achieved. On the above basis, the role of carbon impurities in GaN has been investigated. The two local vibrational modes of isolated CN in GaN have been observed and identified for the first time. The results provide an unambiguous evidence of the substitutional C impurities occupying the N site in C-doped semi-insulating GaN thin films.
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