Damage to epitaxial GaN layer on Al 2 O 3 by 290-MeV 238 U 32+ ions irradiation.

Micro-structural characteristics and electrical properties of an n-type GaN epilayer on Al2 O3 irradiated by 290-MeV 238 U32+ ions to various fluences were investigated using atomic force microscopy (AFM), scanning electron microscopy (SEM), high-resolution X-ray diffraction (HRXRD), and Raman scattering spectroscopy. AFM images show that the nano-hillocks generated, and the diameter and density of the nano-hillocks, increase obviously with increasing ion fluence, accompanied by an increase in surface roughness. SEM images display that the Al, O, and C elements appear on the GaN surface, along with a spiral-like, layered volcanic-cone structure formed at the highest-fluence irradiation. HRXRD reveals that the dislocation density increases, as the lattices gradually expand, and that Ga2 O3 was produced with increasing ion fluence. Raman scattering spectra show that no N and Ga vacancies were produced, the free-carrier concentration decreases, while its mobility first increases and then exhibits a significant reduction with increasing ion fluence.