Samples of Er-doped material were grown with O co-doping via metalorganic vapor phase epitaxy, using 18O. It was found that the Er center which was formed by the reaction of Er and O molecules, Er-2O, produced a sharp high-intensity photoluminescence spectrum. Other centers, which were formed by the reaction of Er with residual O complexes, produced only broad low-intensity spectra. The intensity of the luminescence from the Er-2O center decreased when epitaxial layers were grown onto (100) substrates which were misoriented towards [111]A or [111]B. A decrease was also observed when an epitaxial layer was grown at a lower growth rate. It was suggested that the Er-2O center formed only when an Er atom reacted with an O molecule on an atomically flat (100) surface and became the core of an atomic-step island.

K.Takahei, Y.Horikoshi, A.Taguchi: Materials Science Forum, 1995, 196-201, 639-44