The mechanism for polarity inversion of GaN via a thin AlN layer: direct experimental evidence

Abstract

Lateral-polarity heterostructures of GaN on c-sapphire were prepared by deposition and patterning of a thin low-temperature AlN nucleation layer. Adjacent macroscopic domains were found to have opposite polarity; domains grown on the AlN nucleation layer were Ga-polar while those grown on the nitrided sapphire were N-polar, as confirmed by convergent-beam electron diffraction and Z- contrast images. We directly determined the atomic interface structure between the AlN and c-sapphire with an aberration-corrected scanning transmission electron microscope at ~1.0 � resolution. This is the direct experimental evidence for the origin of the polarity control in III-nitrides. This understanding is an important step toward manipulating polarity in these semiconductors.