Large magnetization in high Gd concentration GaGdN and Si-doped GaGdN grown at low temperatures

GaGdN layers were grown at temperatures below 300 °C by radio-frequency plasma-assisted molecular-beam epitaxy on sapphire substrates. GaGdN samples with high Gd concentration as high as 12.5% were obtained. X-ray diffraction results showed no obvious secondary phase, which means that the phase separation can be suppressed by the growth at low temperatures. Local structure around the Gd atom was investigated by extended x-ray absorption fine structure measurement using Gd L_III edge. It was shown that Gd atoms were mainly incorporated into the Ga sites in the GaGdN layers. All the samples grown at low temperatures exhibited ferromagnetic characteristics. It is considerable that electrons coming from defects, especially, nitrogen vacancy, stabilize ferromagnetism, and that the carrier-induced ferromagnetism occurs in the low-temperature-grown GaGdN. Furthermore, Si was doped into GaGdN layers during growth in order to increase carrier density, and larger magnetization was observed.