Paramagnetic defects in neutron irradiated bulk GaN crystals

The local structure of defects in undoped, Si-doped, and neutron irradiated free standing GaN bulk single crystals, grown by the hydride vapor phase epitaxy (HVPE), has been investigated by employing an X-band electron spin resonance (ESR) spectrometer. The undoped sample was irradiated to a dose of 2 × 10¹⁷ neutrons in an atomic reactor at Korea Atomic Energy Research Institute. The ESR spectrum measured at 8 K of the Si-doped sample shows a broader line width than the undoped one. It reveals that both have only one ESR center with the g-value of g_II = 1.9503 and g_⟂ = 1.9476. The ESR spectrum of neutron irradiated GaN sample shows also the same center but broader line width than that before irradiation. Although no further paramagnetic centers have been detected, the line broadening in both ESR and Raman spectra reveals that neutron irradiation induced some sort of structural disorder in the crystal.