Local structures around Er atoms in GaAs:Er,O studied by fluorescence EXAFS and photoluminescence

We have investigated Er- and O-doped GaAs samples by fluorescence extended X-ray absorption fine structure (EXAFS) measurements in order to clarify the local structures around the Er atoms. The EXAFS analysis revealed that in the range of Er concentration from 2 X 10(18) cm(-3) to 3 X 10(20) cm(-3) the majority of the Er atoms substituted Ga sublattice with two adjacent oxygen atoms (Er-2O center). On the contrary, in the same range of the Er concentration the PL intensity decreased rapidly with the increase of the Er concentration. The EXAFS analysis also indicated that the averaged arrangements of second or third neighbor atoms are different in each sample. Therefore, the Er-2O centers are considered to be further modified by the local structures of those second and even third nearest neighbors, which in turn change their optical characteristics. (C) 2000 Elsevier Science B.V. All rights reserved.