Proton irradiation effects on deep level states in Mg-doped p-type GaN grown by ammonia-based molecular beam epitaxy

The impact of proton irradiation on the deep level states throughout the Mg-doped p-type GaN bandgap is investigated using deep level transient and optical spectroscopies. Exposure to 1.8 MeV protons of 1 × 10¹³cm⁻² and 3 × 10¹³cm⁻² fluences not only introduces a trap with an E_V + 1.02 eV activation energy but also brings monotonic increases in concentration for as-grown deep states at E_V + 0.48 eV, E_V + 2.42 eV, E_V + 3.00 eV, and E_V + 3.28 eV. The non-uniform sensitivities for individual states suggest different physical sources and/or defect generation mechanisms. Comparing with prior theoretical calculations reveals that several traps are consistent with associations to nitrogen vacancy, nitrogen interstitial, and gallium vacancy origins, and thus are likely generated through displacing nitrogen and gallium atoms from the crystal lattice in proton irradiation environment