(Invited) Vacancy-Type Defects and Their Carrier Trapping Properties in GaN Studied by Monoenergetic Positron Beams

Abstract

Positron annihilation is a powerful technique for evaluating point defects in semiconductors. Using this technique, one can detect vacancy-type defects in subsurface regions with high-sensitivity. We have used monoenergetic positron beams to probe native vacancies in GaN grown on Si substrate by metalorganic vapor phase epitaxy. Measurements of Doppler broadening spectra and positron lifetimes indicated that the major defect species in the GaN layers was a Ga vacancy coupled with nitrogen vacancies. The positron trapping rate of the defects decreased with increasing [C], which was attributed to the downward shift of the Fermi level position and the resultant change in the defect charge state. Under illumination, the defect charge state was changed from positive to neutral, which was attributed to the trapping of the excited electrons by the defects. The effect of illumination was suppressed for the GaN layer with [C] = 1018 cm−3, which was ascribed to an excellent electron trapping property of C in GaN.