The electrical activity of defects was investigated, in hydride vapour-phase epitaxial n-type GaN which had been grown onto sapphire, by using deep-level transient spectroscopy, iso-thermal current spectroscopy, photoconductivity decay and electron beam-induced current methods. In order to identify the origin of the defects, the epilayers were bombarded with high-energy protons and their characteristics before and after bombardment were compared. The bombardment generated 2 new deep levels, and significantly increased the electron carrier concentration of as-grown epilayer levels. The photo-current decay could be described by a stretched exponential law, whose slope and time-constant markedly decreased after bombardment. The results were explained in terms of carrier capture at deep levels. The electron beam-induced current analyses, according to the deep-level transient spectroscopic data, revealed an increase in recombination and a different distribution of the recombining centres.

Deep Levels and Irradiation Effects in n-Ga. A.Castaldini, A.Cavallini, L.Polenta: Journal of Physics - Condensed Matter, 2000, 12[49], 10161-7