Annihilation of Nanoscale Inversion Domains in Nitrogen-Polar AlN under High-Temperature Annealing

Inversion domains (IDs) are common defects in N-polar III-nitride thin films grown on sapphire substrates. In this work, the atomic structure and lateral migration of the randomly distributed Al-polar nanoscale IDs in N-polar AlN films subjected to high-temperature thermal annealing are investigated. With the increasing annealing temperature and time, Al-polar AlN IDs gradually shrunk in sizes. The vertical stripes transformed into cone-shaped caps on top of the AlN columns and were completely removed at last. The annihilation of the IDs was explained in terms of the lateral migration of the inversion domain boundary (IDB) induced by the imbalance of the strain state on two sides of the IDB. This work clarifies the evolution mechanism of AlN IDs during high-temperature annealing, providing a promising approach in the realization of uniform-polar AlN template for the development of high-efficiency optoelectronic and electronic devices.