Carrier dynamics in neutron irradiated high-quality epitaxial GaN

The microwave probed photoconductivity (MW-PC), differential absorption (DA) and light induced transient grating (LITG) techniques have been combined to examine carrier recombination and trapping characteristics in intrinsic GaN epi-layers, grown on Ammono substrates before and after neutron irradiation. Carrier lifetime has been examined over a wide interval of carrier injection levels, from low to extremely high, and over a wide range of reactor neutron irradiation fluences. It has been shown that the recombination lifetime decreases hyperbolically from ∼200 ns to ∼2 ps varying excitation density from low to high level as the concentration of radiation defects increases. It has been obtained that the ambipolar diffusion coefficient is nearly invariable and estimated to be 2 cm 2 /s in all the investigated samples irradiated with different fluences. This can be explained by the high concentration of excess carriers employed using LITG and DA techniques. The thermal activation energy of E tr ≈ 0.3 eV, attributed to trapping centres of the intrinsic GaN material, has been estimated using the examined characteristics. The carbon and carbon-oxygen complexes with E tr ≤ 0.4 eV levels in the defect configurational schemes, related to photo-ionization centres revealed within MW probe pulsed photo-ionization spectra, can be the suitable candidates to explain the prevailing trapping centres in the intrinsic and weakly irradiated epi-GaN material.