Investigation of wear-out phenomena in Eu-implanted metal-oxide semiconductor light emitting devices

The anomalous wear-out phenomenon of Eu-implanted MOS based light emitting devices (MOSLED’s) was investigated intensively by many different techniques, on samples exposed to different annealing temperatures and times. It will be shown, that in contrast to other rare earth elements the EL intensity of Eu-implanted SiO2 layers can rise under constant current injection before the known EL quenching will start. Under certain circumstances this rise may amount up to two orders of magnitude. The EL behaviour will be correlated with the microstructural and electrical properties of the devices. Transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy (RBS) were used to trace the growth of Eu / Eu oxide clusters and the diffusion of Eu to the interfaces of the gate oxide layer, which are induced by the annealing process. Current-voltage (I(V)) characteristics, EL decay times (τ) and the evolution of the voltage under constant current injection (Vcc) as well as evolution of the EL spectrum with injected charge (EL(Qinj)) were studied with respect to charging and trapping phenomena in the oxide layer in order to reveal details of the EL excitation mechanism. A qualitative model for the anomalous wear-out phenomenon is proposed.