Self heating during long-term DC-aging is found to be responsible
for the degradation of the electrical and optical characteristics
of blue p-GaN/p-AlGaN/InGaN/n+-GaN/SiC LEDs. Electroluminescence
and Cathodoluminescence studies reveal an additional large optical
band, not observed in unstressed devices, on the p-type side of the
LEDs. Deconvolution procedures shows the band, peaked at about 3.1 eV,
is due to three main emissions at 2.93, 3.08 and 3.23 eV. Deep Level
Transient Spectroscopy reveals the presence of four traps for majority
carriers in p-type GaN. A comparison with the optical spectra suggests
three of them (at 0.12, 0.22 and about 0.5 eV) are responsible for the
additional emissions after stress, while a further trap at 1.21 eV is
considered non-radiative in nature. A thermally activated mechanism
inducing the dissociation of native Mg-H complexes and the subsequent
formation of metastable Mg-H2 complexes is considered responsible
for the LED degradation. The hypothesis is supported by high power
electron beam irradiation during Cathodoluminescence studies which
induced a complete disappearance of the band at 3.1 eV as a consequence
of the dissociation under energetic electron beam of the metastable
Mg-H2 complexes.