Influence of the annealing ambient on structural and optical properties of rare earth implanted GaN

GaN films were implanted with Er and Eu ions and rapid thermal annealing was performed at 1000, 1100 and 1200°C in vacuum, in flowing nitrogen gas or a mixture of NH₃ and N₂. Rutherford backscattering spectrometry in the channeling mode was used to study the evolution of damage introduction and recovery in the Ga sublattice and to monitor the rare earth profiles after annealing. The surface morphology of the samples was analyzed by scanning electron microscopy and the optical properties by room temperature cathodoluminescence (CL). Samples annealed in vacuum and N₂ already show the first signs of surface dissociation at 1000°C. At higher temperature, Ga droplets form at the surface. However, samples annealed in NH₃+N₂ exhibit a very good recovery of the lattice along with a smooth surface. These samples also show the strongest CL intensity for the rare earth related emissions in the green (for Er) and red (for Eu). After annealing at 1200°C in NH₃+N₂ the Eu implanted sample reveals the channeling qualities of an unimplanted sample and a strong increase of CL intensity is observed.