Dislocation filtering and polarity in the selective area growth of GaN nanowires by continuous-flow metal organic vapor phase epitaxy

The early growth stages of GaN nanowires on GaN-on-sapphire templates with a patterned dielectric mask have been characterized by using transmission electron microscopy. The dielectric mask aperture (200-800 nm) determines the presence or absence of threading dislocations arising from the underlying template, which results in dislocation-free nanowires for small apertures and dislocation bending for larger apertures, owing to three-dimensional (3D) growth. The Ga polarity of the underlying template is conserved in all nanowires irrespective of the aperture size, even in regions grown laterally above the mask. The pure Ga polarity assures spatially homogeneous optical properties as evidenced by cathodoluminescence.