The total energy of Er point defects, and of Er defects coupled with native defects, were calculated by using the  ab initio  pseudopotential method. The total-energy calculations indicated that various coupled defects, comprising an Er atom and native defects, would form; depending upon the growth conditions and the Fermi-level position. By investigating the valence charge distribution, it was found that an Er atom formed a strong bond with an As atom. This chemical factor, and the lattice relaxation around the coupled defect, were the main features that stabilized the coupled states. The intra 4f-shell luminescence spectrum of Er was generally complicated, and depended strongly upon the sample preparation method and the growth conditions. It was proposed that this tendency was due to the sample-dependent concentration of various defects that formed complexes with Er.

A.Taguchi, T.Ohno: Physical Review B, 1997, 56[15], 9477-87