**Acknowledgements**

**5. Conclusion**

40 Ion Implantation - Research and Application

ing by RTA at different temperatures.

**2.** Typical XRD profiles were taken for Co<sup>+</sup>

and the substrate structure.

or Ga1−*<sup>x</sup>*

Cr*<sup>x</sup>*

**5.** The coercivity (*H*<sup>c</sup>

175 Oe.

**6.** Comparing Cr+

cm−2 and subsequently annealed at 700, 800 and 900°C and for Cr<sup>+</sup>

**1.** RBS/C measurements on the as-grown GaN samples showed good crystalline quality (*χ*min = 1.3%) and ion-implanted samples showed recovery of lattice damage after anneal-

of 3 × 1016 ions cm−2 and subsequently annealed at 800 and 900°C. In the as-grown samples, three main peaks appeared, corresponding to the expected diffraction from the GaN epilayer and sapphire substrate structure. Comparison of as-grown with the implanted samples at different doses showed that no secondary phase or metal-related peaks were detected in the as-implanted samples and annealed samples from typical XRD spectra. The diffraction patterns only showed the presence of peaks corresponding to the GaN layer

**3.** On diffraction patterns from HR-XRD scans of implanted samples, typical satellite peaks appear at lower side of the main GaN (0002) reflection. The new peaks on the HR-XRD scans are assigned to implantation-induced damage as well as the formation of Ga1−*<sup>x</sup>*

(Ga,Cr)N change due to the presence of Co and Cr, respectively, suggesting that the locations of the new peaks depend on the cobalt or chromium content in the material. The shift of additional peaks towards the high angle side with annealing points to lattice recovery and improvement in the uniformity of GaCoN or GaCrN which may be due to increase in

**4.** Well-defined hysteresis loops were observed even at room temperature by AGM in all implanted and subsequently annealed samples at different temperatures, eliminating the possibility of paramagnetism and superparamagnetism. The analysis of hysteresis loops for the implanted samples helps us to explore the magnetic properties of the material. No lateral shift of hysteresis loops was observed, which, therefore, exclude spin glass behaviour. These findings suggest the presence of ferromagnetic ordering in our implant-

subsequently annealed GaN samples were observed up to 275 Oe and that at 5 × 1016 ions

at 3 ×1016 ions cm−2 and subsequently annealed samples, the coercivity was observed up to

observe that saturation magnetization *Ms* values are almost the same in all samples at room temperature. But at 5 K, the saturation magnetization *Ms* values are almost similar

C. The *Ms* value for Cr<sup>+</sup>

the substitution probability of cobalt or chromium atoms, respectively.

ed samples at room temperature. The room temperature coercivity *H*<sup>c</sup>

was about 100 Oe for all implanted and subsequently annealed samples.

) at 5 K measured by SQUID for Co<sup>+</sup>

implanted and Co+

only for the samples annealed at 800o

cm−2 and subsequently annealed samples were observed up to 600 Oe. For Cr<sup>+</sup>

N in the implanted part of the samples. The lattice constants of (Ga,Co)N and

implanted GaN at doses 3 ×1016 and 5 ×1016 ions

implanted GaN at a dose

Co*<sup>x</sup>* N

measured by AGM

implanted

implanted at 3 × 1016 ions cm−2 and

implanted and subsequently

implanted samples at the same amount of dose, we

Morgan Madhuku acknowledges iThemba LABS and the National Research Foundation of South Africa for financial support.
