Structures and optical properties of Kr23+ and Ne8+-irradiated GaN epi-layers

Epitaxial GaN layers grown by MOCVD on c-plane sapphire substrates were irradiated with 5.3 MeV Kr23+ and 2.3 MeV Ne8+ ions to various fluences. The pristine and the irradiated GaN samples were characterized using high resolution X-ray diffraction (HRXRD), UV–visible transmittance spectrum and Raman scattering spectrum analysis. The HRXRD results show an obvious increase in the FWHM and a decrease in the intensity of the GaN (0 0 0 2) peak with increasing ion fluences. Meanwhile the UV–visible transmittance spectra show a decrease in the band gap value after irradiation. The Raman scattering spectrum shows that new Raman bands around 300 and 670 cm−1 appear with increasing ion fluences. The new Raman bands can be ascribed to disorder-activated Raman scattering (DARS) from the highest acoustic-phonon branch and the optical-phonon branch at the brillouin zone boundaries, respectively.