Effect of Illumination on Positron States in Wide Bandgap Semiconductors

Vacancy-type defects in Mg-implanted GaN were probed using monoenergetic positron beams. For the samples after annealing at 1300 degrees C, the line shape parameter S and the positron lifetime increased under illumination with a 325-run He-Cd laser. The observed increase in the trapping rate of positrons by vacancies was associated with the trapping of the excited electrons by the defects. Native defects in GaN grovn on Si substrate were also studied. A similar illumination effect on the positron annihilation parameters was observed for GaN with the carbon concentration of 2 x 10(16) cm(-3). From the relationship between S and the photon energy, it was found that the transition of an electron from a carbon atom to the vacancies plays an important role in the charge shitt of the vacancies under illumination.