Repeatable phase change in Fe implanted GaN Induced by multi-annealing in reduced atmosphere

Wurtzite GaN(001)-films were implanted with 195 keV 57Fe ions with a fluence Φ = 4*10^{16 cm-2} at room temperature. No secondary phase was detected in as implanted state. In order to reduce the implantation damage and to investigate the formation of secondary phases the implanted samples were annealed at 1073 K in a reduced N2-atmosphere (0.5 bar) for several cycles in a minute range. The formation of secondary phases in Fe implanted GaN upon annealing was detected by means of in-situ x-ray diffraction and conversion electron Mössbauer spectroscopy (CEMS). In contrast to our previous experiments with the annealing in a N2-flow at 1.1 bar pressure [3] no α-Fe cluster were found, but Fe3N. The repeatable phase change from Fe3N at room temperature and Fe3-xN at 1023 K was observed by means of in-situ x-ray diffraction. The diffusion of Fe during the annealing process limits the availability of secondary phase and hence the repeatability. The annealing process is accompanied by a strong diffusion of Fe and dissolution of GaN. Oxygen contamination promotes the dissolution of GaN and the formation of β-Ga2O3. The oxidation is confirmed by CEMS. The ferromagnetism in the samples is related to the presence of Fe3-xN. No DMS related phenomena have been observed. The results demonstrate that by variation of pressure phase compositions, other than α-Fe, are possible. It is expected that by the proper choice of annealing conditions specific secondary phases can be created, leading to different electronic, magnetic and other properties.