Deep levels and irradiation effects in n-GaN

The electrical activity of defects was investigated in hydride vapour phase epitaxy n-type gallium nitride (GaN) grown on sapphire by deep level transient spectroscopy, iso-thermal current spectroscopy, photoconductivity decay measurements and the electron beam induced current (EBIC) method, in order to identify the defect origin, the epilayers were irradiated by high energy protons, and their characteristics before and after irradiation were compared. Irradiation generates two new deep levels and significantly increases the electron carrier concentration of the as-grown epilayer levels. The photocurrent decay is characterized by a stretched exponential law, the slope and time constant of which dramatically decrease after irradiation. The results are discussed in terms of carrier capture at deep levels. EBIC analyses, according to the DLTS findings, revealed an increase in recombination, and also a different distribution of the recombining centres.