title: Lattice Location of Mg in GaN: A Fresh Look at Doping Limitations.
abstract: Radioactive ^{27}Mg (t_{1/2}=9.5  min) was implanted into GaN of different doping types at CERN's ISOLDE facility and its lattice site determined via β^{-} emission channeling. Following implantations between room temperature and 800 °C, the majority of ^{27}Mg occupies the substitutional Ga sites; however, below 350 °C significant fractions were also found on interstitial positions ∼0.6  Å from ideal octahedral sites. The interstitial fraction of Mg was correlated with the GaN doping character, being highest (up to 31%) in samples doped p type with 2×10^{19}  cm^{-3} stable Mg during epilayer growth, and lowest in Si-doped n-GaN, thus giving direct evidence for the amphoteric character of Mg. Implanting above 350 °C converts interstitial ^{27}Mg to substitutional Ga sites, which allows estimating the activation energy for migration of interstitial Mg as between 1.3 and 2.0 eV.
authors.affiliation: Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, 2695-066 Bobadela, Portugal.
authors.forename: U
authors.initials: U
authors.lastname: Wahl
authors.affiliation: KU Leuven, Instituut voor Kern- en Stralingsfysica, 3001 Leuven, Belgium.
authors.forename: L M
authors.initials: LM
authors.lastname: Amorim
authors.affiliation: KU Leuven, Instituut voor Kern- en Stralingsfysica, 3001 Leuven, Belgium.
authors.forename: V
authors.initials: V
authors.lastname: Augustyns
authors.affiliation: Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, 2695-066 Bobadela, Portugal.
authors.forename: A
authors.initials: A
authors.lastname: Costa
authors.affiliation: Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, 2695-066 Bobadela, Portugal.
authors.forename: E
authors.initials: E
authors.lastname: David-Bosne
authors.affiliation: KU Leuven, Instituut voor Kern- en Stralingsfysica, 3001 Leuven, Belgium.
authors.forename: T A L
authors.initials: TA
authors.lastname: Lima
authors.affiliation: KU Leuven, Instituut voor Kern- en Stralingsfysica, 3001 Leuven, Belgium.
authors.forename: G
authors.initials: G
authors.lastname: Lippertz
authors.affiliation: Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, 2695-066 Bobadela, Portugal.
authors.forename: J G
authors.initials: JG
authors.lastname: Correia
authors.affiliation: Centro de Física Nuclear da Universidade de Lisboa, 1649-003 Lisboa, Portugal.
authors.forename: M R
authors.initials: MR
authors.lastname: da Silva
authors.affiliation: Cambridge Centre for Gallium Nitride, University of Cambridge, Cambridge CB3 0FS, United Kingdom.
authors.forename: M J
authors.initials: MJ
authors.lastname: Kappers
authors.affiliation: KU Leuven, Instituut voor Kern- en Stralingsfysica, 3001 Leuven, Belgium.
authors.forename: K
authors.initials: K
authors.lastname: Temst
authors.affiliation: KU Leuven, Instituut voor Kern- en Stralingsfysica, 3001 Leuven, Belgium.
authors.forename: A
authors.initials: A
authors.lastname: Vantomme
authors.affiliation: KU Leuven, Instituut voor Kern- en Stralingsfysica, 3001 Leuven, Belgium.
authors.forename: L M C
authors.initials: LM
authors.lastname: Pereira