Growth of Fe-doped GaN by RF plasma-assisted molecular beam epitaxy

Iron-doped GaN films were grown using plasma-assisted molecular beam epitaxy (PA-MBE) for various III/V ratios. Iron concentrations were determined by calibrated secondary-ion mass spectroscopy (SIMS), and films were characterized by high-resolution X-ray diffraction (HR-XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The iron incorporation strongly depended on the growth conditions, with increasing incorporation with decreasing III/V ratio. The behavior was explained by promotion of surface segregation of iron by the gallium adlayer and droplets. AFM indicated no effect of iron doping on surface morphology. Precipitation of intermetallic FeGa3 was found for gallium droplet regime growth and high iron fluxes. Nitrogen-rich growth resulted in significantly enhanced iron incorporation and reduced segregation, and nitrogen-rich iron-doped films were grown for iron concentrations of up to 1×1019 cm−3 with no evidence of iron-related phase precipitation or crystalline degradation. Highly-doped nitrogen-rich films were overgrown with gallium-rich GaN, resulting in specular surface morphologies and sharp turn-on and turn-off of the iron profile in SIMS. Similarities to the reported behavior of manganese doping of GaN suggests that surface segregation of transition metal dopants may be important for PA-MBE growth.