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

摘要

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 SiO_2 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) cm~2. This is probably associated with an increase in the concentration of oxygen deficiency centers as well as with strained and dangling bonds in the SiO_2 matrix which leads to an enhanced scattering of hot electrons and a decrease in the excitation cross section of the main EL lines of RE~(3+) ions. For the main EL lines of Tb~(3+) and Eu~(3+) ions the relation of the EL quenching to negative and positive charge generation in the SiO_2 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 RE~(3+) excitation. At high levels of the injected charge (more than 2 × 10~(20) e/cm~2) a second stage of the EL quenching was observed which was contributed to a positive charge accumulation in the SiO_2 at a distance beyond the tunneling distance from the SiO_2-Si interface. In case of Eu-implanted SiO_2 the quenching of the main EL line of Eu~(3+) is mostly correlated with positive charge trapping in the bulk of the dielectric. A model of EL quenching of the main Eu~(3+) line is proposed.