The Mu+ defect centers were studied by using muon nuclear-quadrupole level-crossing resonance and zero-field muon spin depolarization measurements. The dominant Mu+ center was highly mobile, but quadrupole level-crossing resonance spectra identified a second static Mu+ state at AB||(N) sites in both nitrides. This state became mobile above 800K in AlN, but converted to Mu- above 200K in GaN. Zero-field data characterized the local fields and motional properties for this state in AlN. Above 1100K, the mobile Mu+ in AlN showed strong interactions and trapping at another defect.

Positively Charged Muonium Centers in Aluminum and Gallium Nitrides. R.L.Lichti, S.F.J.Cox, E.A.Davis, B.Hitti, S.K.L.Sjue: Physica B, 2001, 308-310, 73-6