Proton-irradiation-induced degradation in GaN-based UV LEDs: Role of unintentionally doped carbon

Abstract

Degradation and defect evolution in GaN-based UV LEDs under 3 MeV proton irradiation were throughly investigated in this work. Combined with the yellow luminescence band at ∼2.2 eV in photoluminescence spectra with the energy level of Ev + 0.16 eV extracted by deep-level transient spectroscopy measurement, an intrinsic CN-related defect with an abnormally decreased concentration after irradiation was identified. Based on energy levels, the spatial configuration of defects, and their correlations, several possible origins and evolution processes of the defects are systematically discussed. A defect evolution model under proton irradiation was established: C atoms departed from the CN-related defect aligned along the dislocation in the active region stimulated by the displacement damage effect, leaving behind a nitrogen vacancy (VN) aligned along the dislocation, accompanied by the generation of a non-interacting carbon interstitial (Ci). Both the increased VN and Ci were found to contribute jointly to the decrease in optical power and the increase in leakage current. This indicates that carbon—a common unintentional dopant in GaN-based optical devices—can be an important factor in the degradation of GaN-based UV LEDs under proton irradiation, and should be further noted in radiation resistance applications.