Incorporation and stability of erbium in sapphire by ion implantation

Precise results on the lattice site location and stability of Er implanted sapphire using the RBS/channeling technique are reported. The Er ions were implanted into <0001> and (01I0) cut samples of a-Al₂O₃ single crystals, at room and liquid nitrogen temperatures, with 200 keV energy at fluences between 8 x 10¹³ and 4 x 10¹⁵ Er⁺/cm². The implantation of 8 X 10¹³ Er⁺/cm² (0.01 at%) at room temperature leads to the incorporation of 70% of the Er ions near the free octahedral site (0.8 Å displaced) along the c-axis. From the remaining fraction of Er ions, at least 20% can be in a tetrahedral site. At liquid nitrogen temperature the fluence of 6 x 10¹⁴ Er⁺/cm² amorphizes sapphire, while at room temperature a fluence an order of magnitude higher produces only a damaged buried layer. The annealing at temperatures higher than 1200°C leads to the recrystallization of the amorphous layer, but the Er ions segregate to the surface or precipitate. For the samples implanted at room temperature, the annealing leads to a higher incorporation of Er in the sapphire lattice and only a small fraction segregates to the surface at 1500°C.