Spinodal decomposition and secondary phase formation in Fe-oversaturated GaN

The flash-lamp annealing technique was applied to a GaN epilayer implanted with Fe in order to investigate the recovery of the crystal structure and the process of secondary phase formation. In the as-implanted state a spinodal decomposition occurs due to the oversaturation of Fe in GaN and a behavior similar to a spin glass is observed. Precipitation occurs even after annealing for the shortest annealing time of 3 ms. Iron nitrides as well as bcc-Fe are formed upon annealing for 20 ms and are responsible for the ferromagnetic response. No indication of the formation of a diluted magnetic semiconductor is observed. The correlation between the structure, magnetism and Fe-charge state was determined by x-ray diffraction, magnetometry and M\"ossbauer spectroscopy measurements.