A relationship between intra-4f transitions of Er and vacancy-type defects in Er-doped GaN was studied by using a mono-energetic positron beam. Doppler broadening spectra of the annihilation radiation were measured for Er-doped GaN grown by molecular beam epitaxy. A clear correlation between the defect concentration and the photoluminescence  intensity was observed. The major defect species detected by positrons was identified as a Ga vacancy VGa, and its concentration increased with increasing Er concentration [Er]. For the sample with [Er] = 3.3at%, the maximum integrated intensity of photoluminescence was observed. The VGa concentration was above 1018/cm3 and additional vacancies such as divacancies started to be introduced at this Er concentration. For the sample with higher [Er], the photoluminescence intensity decreased, and the mean size of vacancies decreased due to an introduction of precipitates and/or metastable phases.

Vacancy-Type Defects in Er-Doped GaN Studied by a Monoenergetic Positron Beam. A.Uedono, C.Shaoqiang, S.Jongwon, K.Ito, H.Nakamori, N.Honda, S.Tomita, K.Akimoto, H.Kudo, S.Ishibashi: Journal of Applied Physics, 2008, 103[10], 104505