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.
We report on the fabrication and characterization of Si/SiO2 Fabry-Perot microcavities. These structures are used to enhance the external quantum emission along the cavity axis and the spectral purity of emission from Rare earth doped and undoped SiOx (x <= 2)films that are used as active media to fabricate a Si based RCLED (Resonant Cavity Light emitting Devices). These structures are fabricated by chemical vapour deposition on a silicon substrate. The microcavities are tuned at different wavelengths: 540nm, 980nm, 1540nm, 780nm and 850nm (characteristic emission wavelength respectively for Tb, Yb and Er and Silicon Rich Oxide (SRO)). The reflectivity of the microcavities is of 97% and the factor quality ranges from 50 (for the cavity tuned at 540nm) to 95 (for the cavities tuned at 980nm and 1540nm) and 150 (for the cavity tuned at 780nm and 850 nm). These cavities have been characterized by TEM analysis to evaluate films uniformity, thickness and densification after annealing process for temperature ranging from 800° to 1100°C. The reflectivity and photoluminescence spectra show resonant wavelengths in agreement with the calculated values. A new structure to electrically pump the active media has been designed. The electrical properties of the active media have been analysed. An enhancement of the photoluminescence signal of twenty times have been achieved for the selected emission wavelength.
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