High efficiency light emitting devices in silicon

Abstract

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. They exhibit strong 1.54 μm electro-luminescence (EL) at 300 K with a 10% external quantum efficiency, comparable to that of standard light emitting diodes using III–V semiconductors. Emission at different wavelengths has been achieved incorporating different rare earths (terbium (Tb) and ytterbium (Yb)) in the gate dielectric. The external quantum efficiency depends on the rare-earth ions incorporated and ranges from 10% (for a Tb doped MOS) to 0.1% (for an Yb doped MOS). 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 silicon rich oxide (SRO) films as gate dielectric. These devices show a high stability, with an external quantum efficiency reduced to 0.2%. In these devices, Er pumping occurs partially by hot electrons and partially by energy transfer from the Si nanostructures to the rare-earth ions, depending on Si excess in the film. Si/SiO 2 Fabry–Perot microcavities have been fabricated to enhance the external quantum emission along the cavity axis and the spectral purity of emission from the films that are used as active media to fabricate a Si-based resonant cavity light emitting diode (RCLED). These structures are fabricated by chemical vapour deposition on a silicon substrate. The microcavities are tuned at different wavelengths (nm): 540, 980 and 1540 (characteristic emission wavelengths, respectively, for Tb, Yb and Er). The reflectivity of the microcavities is about 97% and the quality factor ranges from 60 (for the cavity tuned at 980 nm) to 95 (for the cavities tuned at 540 and 1540 nm).