The lattice location of Er was studied by using emission channelling techniques. The angular distribution of conversion electrons which were emitted by the decay, 167Tm → 167mEr, was monitored by using a position-sensitive detector following room-temperature implantation and annealing at up to 950C. In O rich Czochralski material, a distinct decrease in the near-tetrahedral Er fraction was observed upon annealing at 800C and above; thus indicating a strong interaction of the parent Tm with O-related defects. On the other hand, since the concentration of implanted Tm/Er was identical in float-zone and Czochralski material, it appeared that the formation of simple clusters of Tm/Er was less efficient. The results provided direct evidence that Er was stable at tetrahedral interstitial sites in float-zone material. It was also confirmed that rare-earth atoms strongly interacted with O; and finally led to their incorporation at low-symmetry lattice sites in Czochralski material.

U.Wahl, A.Vantomme, J.De Wachter, R.Moons, G.Langouche, J.G.Marques, J.G.Correia, Isolde: Physical Review Letters, 1997, 79[11], 2069-72