Defects in Eu- and Tb-doped GaN films, grown onto sapphire substrates, were studied by means of gas-source molecular-beam epitaxy with a mono-energetic positron beam. In both Eu- and Tb-doped samples, vacancy clusters were observed which consisted of 2 or more vacancies. These defects were introduced by replacing Ga with rare-earth elements; resulting in distortion of the host matrix. A study was made of the correlation between luminescence originating from the intra-4f-transitions of Eu3+ and the crystal quality of

the GaN film. In film doped at 2at%Eu, the mean open volume of the vacancies near to the interface between the GaN film and the sapphire substrate was found to be larger than that in the sub-surface region. The increase in the open volume of the defects correlated with the lowering coordination symmetry of Eu3+ and the increase in the transition rate of its 4f-electrons.

Defects in Eu- and Tb-Doped GaN Probed using a Monoenergetic Positron Beam. A.Uedono, H.Bang, K.Horibe, S.Morishima, K.Akimoto: Journal of Applied Physics, 2003, 93[9], 5181-4