Investigation of Helium-Induced lattice disorder in GaN and AlN under precisely localized irradiation

This study presents an in-depth analysis of substrate lattice disorder in GaN and AlN, particularly GaN, under controlled precise irradiation achieved by helium ion microscopy. GaN was exposed to various irradiation fluences (0.01–0.1 nC/μm) at beam energies of 15 keV and 35 keV, with subsequent lattice disorder characterized using scanning, high resolution transmission electron microscopy, and energy dispersive spectroscopy. The results reveal that the defective region in GaN is characterized as a vase-shaped profile comprising a bulbous region filled with helium bubbles attached to dislocation loops and a locally amorphous neck region. As the irradiation fluence increases or the beam energy decreases, the defects become denser, leading to the formation of complex defective structures and severe lattice distortions. Under irradiation condition of 15 keV paired with 0.1 nC/μm, crystallographic misorientation, surface swelling, nanocracks formed by the lateral coalescence of helium bubbles, the deficit of N atoms and enriched Ga nanocrystals are identified. The AlN substrate exposed to irradiation exhibits similar damage profiles to GaN, but there is no preferential disordering of the AlN surface. This study enhances the understanding of ion-induced lattice disorder in III-nitrides under light gas ion implantation, providing valuable insights into the irradiation response of III-nitrides.