Ferromagnetism in GaN induced by Fe ion implantation

Abstract

We report about magnetic and structural studies on p-type wurtzite GaN implanted with F57e with fluences from 1×1016 cm−2 to 1.6×1017 cm−2 at different temperatures and subsequently subjected to thermal treatment. X-ray diffraction (XRD), transmission electron microscopy (TEM), conversion electron Mössbauer spectroscopy (CEMS), and superconducting quantum interference device magnetometry (SQUID) were used for the crystallographic, electronic, and magnetic characterization of the samples. Room temperature (RT) ferromagnetism was observed in GaN after implantation at 623 K with different fluences and is mainly ascribed to α-Fe precipitations. An additional contribution to the ferromagnetic signal is observed in a Mössbauer spectrum and as a magnetization loop in SQUID in a sample implanted with lowest fluence at 623 K which cannot be related to α-Fe. After implantation at RT with low fluences no ferromagnetism was observed by means of the SQUID. However, in the CEMS a magnetic hyperfine field of 6.8 T was used to fit the experimental spectrum and is discussed in terms of possible origin. Samples implanted at 240 K do not exhibit ferromagnetic properties. Thus, precipitation of α-Fe was successfully reduced by decreasing the implantation temperature. However, this was accompanied by an enhanced crystal damage. Annealing between 973 K and 1123 K resulted in most cases predominantly in the formation of α-Fe clusters. Thermal treatment brought no significant recovery of the crystallinity as was verified by the RBS channeling measurements.