Micro Raman analysis of MOCVD grown gallium nitride epilayers irradiated with light and heavy ions

We have investigated the micro Raman spectra of pristine and 100 MeV swift heavy ions namely oxygen and silver ions, irradiated at fluences of 1 × 1012 and 1 × 1013 ions cm−2 on metal organic chemical vapor deposition (MOCVD) grown GaN epilayers. X-ray diffractometer (XRD) confirmed the wurtzite nature of GaN. Pristine Raman spectra show the good quality of epilayers. On irradiation with light ion, O7+, the order of defects increases and the annealing or ordering of defects occurs in the crystal at higher fluencies. For heavy ion, Ag12+, irradiation results in the increase of disorder for all fluences. A Lorentzian line shape model has been fitted to the Raman spectra of optical phonon mode of E2H (high) and A1(LO) peaks. Biaxial stress (σ), carrier concentration (n) and phonon life-time of first order optical phonon (τ) are deduced from the Raman shift of E2H (high) and A1(LO) mode for all the irradiated samples. While with light ion irradiation, σ deceases where as n and τ increases and for heavy ion irradiation σ and n increases and τ decreases.