On the formation of secondary phases in Fe implanted GaN

The request for room-temperature diluted magnetic semiconductors resulted in a large interest in GaN containing transition metals. Recent investigations have shown that beside of the real dilute state spinodal decomposition as well as the formation of secondary phases may play an important role in the discussion of the origin of the ferromagnetism [1, 2].
In this study, the dynamics of formation of secondary phases is investigated on GaN epilayers deposited on sapphire and implanted with 57Fe+ ions (3, 8 and16 • 1016 cm−2) at room temperature. Samples were annealed at 750° – 1200° C in N2 and Ar flow for durations between some ms and some minutes.
The formation of secondary phases in Fe implanted GaN upon annealing a N2-flow was detected ex-situ by means of x-ray diffraction and Mössbauer spectroscopy and supported by SQUID magnetometry. During annealing in reduced N2 atmosphere the reversal phase change from Fe3N at room temperature to Fe2.4N at 1023 K was observed by means of in-situ x-ray diffraction. Samples, annealed by a flash lamp in an Ar flow show the formation of different secondary phases depending on annealing time and temperature.

[1] Bonanni et al., PRL 101, (2008) 135502
[2] Li et al., Journal of Crystal Growth 310, (2008) 3294–3298