Si-based rare-earth-doped light-emitting devices

摘要

We report on the fabrication and performances of highly efficient Si-based light sources. The devices consist of MOS structures with erbium (Er) implanted in the thin gate oxide. The devices exhibit strong 1540 nm electroluminescence at 300K with a 10% external quantum efficiency, comparable to that of standard light emitting diodes using III-V semiconductors. Emission at different wavelenghts has been achieved incorporating different rare earths (Ce, Tb, Yb, Pr) in the gate dielectric. RE excitation is caused by hot electrons impact and oxide wearout limits the reliability of the devices. Much more stable light emitting MOS devices have been fabricated using Er-doped SRO (Silicon Rich Oxide) films as gate dielectric. These devices show a high stability, with an external quantum efficiency reduced to 0.2%. In these devices different pumping mechanisms for the Er ions are simultaneously operating: Er can be excited by direct hot electron impact (like in stoichiometric oxide MOS) and by energy transfer from excited Si nanostructures, depending on the Si excess in the film. We propose a model to describe the electrical conduction mechanism in a Silicon Rich Oxide film. The electrical characteiristics can be fitted by a Schottky emission mechanism at low electrical fields and by a SCLC(Space Charge Limited Conduction) model for high elctrical fields. Data obtained from C-V measurements confirm the proposed model.