title: Muonium as a shallow center in GaN.
abstract: A paramagnetic muonium (Mu) state with an extremely small hyperfine parameter was observed for the first time in single-crystalline GaN below 25 K. It has a highly anisotropic hyperfine structure with axial symmetry along the <0001> direction, suggesting that it is located either at a nitrogen-antibonding or a bond-centered site oriented parallel to the c axis. Its small ionization energy (<or=14 meV) and small hyperfine parameter (approximately 10(-4) times the vacuum value) indicate that muonium in one of its possible sites produces a shallow state, raising the possibility that the analogous hydrogen center could be a source of n-type conductivity in as-grown GaN.
authors.affiliation: Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Shimomura
authors.forename: R
authors.initials: R
authors.lastname: Kadono
authors.forename: K
authors.initials: K
authors.lastname: Ohishi
authors.forename: M
authors.initials: M
authors.lastname: Mizuta
authors.forename: M
authors.initials: M
authors.lastname: Saito
authors.forename: K H
authors.initials: KH
authors.lastname: Chow
authors.forename: B
authors.initials: B
authors.lastname: Hitti
authors.forename: R L
authors.initials: RL
authors.lastname: Lichti