Symmetry properties of Er³⁺ related centers in In _1-xGa_xP with low alloy compositions

The symmetry properties of Er³⁺-related centers in InP and In_1-xGa_xP (x=0.08) epitaxial layers are determined using the method of polarized excitation spectroscopy. It is shown that the Er ³⁺-related luminescence is strongly polarized under polarized excitation. The polarization measurements indicate the low symmetry of these centers. Two transition mechanisms are proposed to explain the polarized luminescence. The first mechanism involves excitation of the intra-4f-shell electron into higher lying excited states of the Er³⁺ ion. A second mechanism involves the recombination of an exciton bound to an Er-related trap with a subsequent Auger excitation of the 4f shell.