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

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 similar to 1.0 A 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. (c) 2007 American Institute of Physics.