The effect of rare-earth clustering on charge trapping and electroluminescence in rare-earth implanted metal-oxide-semiconductor light-emitting devices.

The effect of rare-earth clustering in dielectric media on the electroluminescence (EL) intensity, the charge trapping and the EL quenching was investigated using the example of Tb and Eu-implanted SiO₂ layers. It was shown that the increase in the REO_X cluster size induced by an increase in the furnace annealing temperature resulted in an increase in the concentration of electron traps with capture cross sections from 2×10^-15 to 2×10^-18 cm². This is probably associated with an increase in the concentration of oxygen deficiency centers as well as with strained and dangling bonds in the SiO₂ matrix which leads to an enhanced scattering of hot electrons and a decrease in the excitation cross section of the main EL lines of RE³⁺ ions. For the main EL lines of Tb³⁺ and Eu³⁺ ions the relation of the EL quenching to negative and positive charge generation in the SiO₂ was considered. It was demonstrated that in case of REO_X nanoclusters with small sizes (up to 5 nm) the EL quenching process can mainly be explained by a defect shell model which suggests the formation of negatively charged defect shells around the nanoclusters leading to a Coulomb repulsion of hot electrons and a suppression of the RE³⁺ excitation. At high levels of the injected charge (more than 2×10²⁰ e/cm²) a second stage of the EL quenching was observed which was contributed to a positive charge accumulation in the SiO₂ at a distance beyond the tunneling distance from the SiO₂[Single_Bond]Si interface. In case of Eu-implanted SiO₂ the quenching of the main EL line of Eu³⁺ is mostly correlated with positive charge trapping in the bulk of the dielectric. A model of EL quenching of the main Eu³⁺ line is proposed. [ABSTRACT FROM AUTHOR]