Effect of Gd implantation on the structural and magnetic properties of GaN and AlN

Gd+ ions were implanted at total doses of 3-6× 1014 cm2 into single-crystal GaN or AlN epilayers grown on sapphire substrates and annealed at 700-1000°C. The implanted Gd showed no detectable diffusion in either material after annealing, as measured by secondary ion mass spectrometry, corresponding to a diffusion coefficient <8× 10-12 cm2 s-1. Under all annealing conditions, x-ray diffraction shows the formation of second phases. In the case of GaN, these include Gd3 Ga2, GdN, and Gd, while for AlN only Gd peaks are observed. Both the GaN and AlN show high saturation magnetization after annealing at 900°C (∼15 emu cm-3 for GaN and ∼35 emu cm-3 for AlN). The magnetization versus temperature characteristics of the Gd-implanted GaN show a blocking behavior consistent with the presence of precipitates, whereas the AlN shows a clear difference in field-cooled and zero-field-cooled magnetization to above room temperature which may also be due to Gd inclusions.