GaN:Co epitaxial layers grown by MOVPE

• Epitaxial growth of in-situ cobalt doped gallium nitride.
• Correlation of GaN–CoN phase diagram calculation with experimental results.
• Extremely low solubility of cobalt in GaN can be overcome by non-equilibrium deposition.
• Formation of cobalt nanoclusters in GaN:Co layers at high temperature.
• Ferromagnetism of GaN:Co layers persisting at room temperature.

We present a growth of GaN layers doped by cobalt using low pressure metalorganic vapor phase epitaxy on c-plane sapphire substrates. The in situ doping of GaN by Co was performed by the decomposition of bis(cyclopentadienyl)cobalt precursor. Three parameters, the temperature and pressure of the deposition and the Ga/Co ratio in the gas phase, influencing cobalt concentration were investigated. The obtained results were confronted with the thermodynamic predictions of Co solubility within GaN lattice and electronic structure calculations of GaN:Co. The magnetic properties of GaN:Co thin films were investigated using superconducting quantum interference device magnetometer. In addition, the layers were characterized by Raman and photoluminescence spectroscopy and atomic force microscopy. The concentration of Co was measured using electron microprobe and depth profile was measured using secondary ion mass spectroscopy. Room temperature ferromagnetic ordering was observed on the Co doped GaN layers.