Direct heteroepitaxial lateral overgrowth of GaN on stripe-patterned sapphire substrates with very thin SiO₂ masks

Direct heteroeptaxial lateral overgrowth of GaN was performed on sapphire substrates by low-pressure metalorganic chemical vapor deposition. The substrates were patterned with very thin SiO₂ stripes with the thickness of 200~300 Å. The growth was carried out by a two-step condition. In the first step for facet-controlled epitaxy, the formation of a triangular cross-section of GaN stripes grown directly on the patterned sapphire was achieved to terminate threading dislocations (TDs) in the opening regions on the inclined {11-22} facets. During the second step for lateral growth, the TDs were bended completely by strong lateral overgrowth. The densities of the step terminations in atomic force microscopic images, corresponding screw- or mixed-type TDs were effectively reduced to less than 10⁷ cm ^-2 over the entire region. The crystallographic tilt between the mask and the opening regions was also well suppressed by using the very thin SiO₂ mask as thick as GaN nucleation layer.