Three-dimensional facet structure of GaN has been fabricated on dot-patterned GaN (0001)/sapphire substrates using SiO2 masks via selective epitaxial growth by metalorganic vapor phase epitaxy. The dot patterns are hexagons with width of 5 µ m and spacing of 10 µ m. The facet structure comprises a hexagonal pyramid covered with six {11̄01} facets. A stable and self-limited (0001) facet appears on the top, depending on growth conditions. The area of the (0001) facet increases with increasing growth temperature or with decreasing flow rate of trimethylgallium. The (0001) facet formation is determined by the diffusion length of a Ga atom on the (0001) surface.
Three-dimensional GaN pyramids have been successfully obtained on dot-patterned GaN(0001)/sapphire substrates by using the selective MOVPE technique. The dot-pattern is a hexagon arranged with a 5μm width and a 10μm spacing. The GaN structure comprises a hexagonal pyramid covered with six {11ȃ01} pyramidal facets on the side or a frustum of a hexagonal pyramid having a (0001) facet on the top. The facet formation mechanism has been investigated by observing the facet structure with the growth time. The {11ȃ01} facets are very stable during the growth. The (0001) facet growth is dominant at the initial growth but almost stops at a certain growth time and then the facet structure is maintained. The appearance of the self-limited (0001) facet is attributed to the balance of flux between incoming Ga atoms from the vapor phase to the (0001) surface and outgoing Ga atoms from the (0001) surface to the {11ȃ01} surface via migration. The longer the diffusion length of the Ga atoms on the (0001) surface is, the more the surface migration is enhanced, resulting in the appearance of the wider (0001) facet on the top.
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