Structural and optical investigation of nonpolar α-plane GaN grown by metal–organic chemical vapour deposition on r-plane sapphire by neutron irradiation

Nonpolar (11\bar20) α-plane GaN films are grown by metal-organic chemical vapour deposition (MOCVD) on r-plane (1\bar102) sapphire. The samples are irradiated with neutrons under a dose of 1\times10¹⁵ cm^-2. The surface morphology, the crystal defects and the optical properties of the samples before and after irradiation are analysed using atomic force microscopy (AFM), high resolution X-ray diffraction (HRXRD) and photoluminescence (PL). The AFM result shows deteriorated sample surface after the irradiation. Careful fitting of the XRD rocking curve is carried out to obtain the Lorentzian weight fraction. Broadening due to Lorentzian type is more obvious in the as-grown sample compared with that of the irradiated sample, indicating that more point defects appear in the irradiated sample. The variations of line width and intensity of the PL band edge emission peak are consistent with the XRD results. The activation energy decreases from 82.5 meV to 29.9 meV after irradiation by neutron.