Defect-enhanced ferromagnetism in Gd- and Si-coimplanted GaN

GaN grown by metal-organic chemical vapor deposition was coimplanted with Gd+ ions with energy of 155 keV and dose of 2.75×1010 cm−2 and Si4+ ions with energies of 5 and 40 keV and corresponding doses of 8×1011 and 3.6×1012 cm−2. The implanted samples were not annealed before characterization. X-ray diffraction measurements revealed that the implanted GaN exhibited no secondary phase formation or clustering effects attributable to Gd. Superconducting quantum interference device magnetometer measurements indicated that Gd- and Si-coimplanted GaN exhibited about a 400% higher magnetic moment than a Gd-implanted GaN thin film. This emphasizes the role of defects in producing large saturation magnetization in Gd-doped GaN. Both types of films displayed ferromagnetic ordering and Curie temperatures above room temperature. The higher magnetic moment was displayed when the magnetic field was applied perpendicular to the sample surface (parallel to the c-axis of the sample), suggesting the polarization field in wurtzite GaN plays a crucial role.