Nonpolar a-GaN epilayers with reduced defect density using patterned r-plane sapphire substrates

Nonpolar a-GaN films were grown on patterned r-plane sapphire substrate (r-PSS) with hemispherical shape pattern by metalorganic chemical vapor deposition. Dislocations originating from the side edge of hemisphere patterns in flat sapphire substrate region were inclined to ∼±60°. The initial GaN was elongated along the ridges of the hemisphere pattern and showed different crystal orientations. This was laterally overgrown by fast deposition from the flat sapphire substrate region. Defects in the a-GaN films on the hemisphere patterns were significantly reduced, because of the inclination of the defects and the epitaxial lateral overgrowth. In addition, additional defects such as voids and zigzag shaped prismatic stacking faults (PSFs) were generated on the top of the r-PSS. For the α-GaN films on the r-PSS, the densities of the basal stacking faults and partial dislocations were reduced to 8.0 × 10⁵ cm^-1 and 8.4 × 10⁹ cm^-2, respectively. Consequently, the nonpolar a-GaN films on the hemispherical r-PSS exhibited superior crystal quality with reduced defect density, even though additional PSFs were formed on the r-PSS.