The local structure of defects in undoped, Si-doped and neutron-irradiated free-standing bulk single crystals (grown via hydride vapor phase epitaxy) was investigated by using an X-band electron spin resonance spectrometer. The undoped sample was irradiated to a dose of 2 x 1017 neutrons in an atomic reactor. The electron spin resonance spectrum of the Si-doped sample, measured at 8K, exhibited a broader line-width than the undoped one. It revealed that both had only one electron spin resonance center, with values of g|| = 1.9503 and g = 1.9476. The electron spin resonance spectrum of neutron-irradiated samples also exhibited the same center, but with a broader line-width than that before irradiation. No further paramagnetic centers were detected, but the line-broadening in the electron spin resonance and Raman spectra revealed that neutron irradiation induced some form of structural disorder.

Paramagnetic Defects in Neutron Irradiated Bulk GaN Crystals. J.H.Kim, I.W.Park, S.H.Choh, S.S.Park, B.G.Kim, Y.H.Kang: Physica Status Solidi C, 2003, 0[2], 597-600