Polarity dependent radiation hardness of GaN

The lattice polarity dependent tolerance of displacement damage was studied for GaN by irradiating its +c and -c surfaces with a proton beam of 8 MeV. In agreement with the in-situ monitored increase of electrical resistance during irradiation, post-irradiation analysis by positron annihilation measurement revealed that the +c surface had a higher tolerance compared with that of the -c one. These results indicate that the defect introduction rate depends on the incident axis of proton beams.