Comparative studies on irradiation effects of GaN and InxGa1-xN films induced by energetic ions

Surface morphologies, microstructures and optical properties of GaN and In_xGa_1-xN films irradiated by 8-MeV Xe¹⁹⁺ ions at different fluences were comparatively investigated by AFM, HRXRD and UV-Vis spectra, respectively. AFM observations revealed that nano-hillock defects were grown out from the irradiated GaN surfaces and their density increases obviously, accompanied by an initial reduction and then an increase, followed by a diminishment in their surface roughness, with increasing irradiation fluences. While for In_xGa_1-xN films, V-shaped pits appeared on their surfaces after irradiation and the surface roughness rises generally with fluences. However, no significant changes in pit densities were observed with fluences. HRXRD analysis displayed that dislocation density and distortion parameter of both nitride films first slightly decrease and then rapidly raise with fluences, along with a gradual lattice expansion. Compared with GaN, the In_xGa_1-xN films presented a notable expansion. Analyses from UV-Vis spectra showed that the Urbach energy of GaN films first slightly reduces and then significantly rises with fluences. And, their band-gap energy of both nitride films exhibited reverse trends to Urbach energy. In contrast to GaN, In_xGa_1-xN films presented a sensitive change in Urbach energy and band-gap energy under the same fluences. The underlying mechanisms were discussed in detail.