Hexagonal GaN films were grown on Si(111) covered with a thin flat SiC buffer layer under both N- and Ga-rich growth conditions. A flat 2.5-nm-thick SiC layer was an effective buffer layer for GaN growth. The growth mode and microstructure of GaN depended strongly on the Ga/N flux ratios. Under N-rich growth conditions, the growth mode was three dimensional; GaN showed statistical roughening of the surface and a characteristic columnar structure. Under Ga-rich conditions, the GaN growth mode was two dimensional; GaN films with a flat surface and an almost stacking-fault-free microstructure were obtained. The two-dimensional growth mode was facilitated by strong wetting between Ga and SiC(111) at the first Ga-layer deposition on SiC.
The generation of misfit dislocations has been investigated on epitaxial silicon wafers with boron-doped substrates, as a function of the film thickness and the misfit resulting from the difference in lattice parameters between the film and the substrate. Critical values of the film thickness hc and of the misfit fc required to form misfit dislocations were found to be hc=2.4–-2.9 μ for the interfacial misfit of 0.019% and fc=0.003–0.006% for relatively large film thickness, where the interfacial energy approaches that of infinitely thick film. These results were analyzed in terms of van der Merwe's theory and a good agreement was found between the experiment and the theory. The density of misfit dislocations was observed to increase with the interfacial misfit or with the film thickness. The relation between bending of the specimens associated with the misfit and the film thickness was studied. Some properties of misfit dislocations are described.
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