Rare-earth-doped nanocrystalline silicon: excitation and de-excitation mechanisms and implications for waveguide amplifier applications

Excitation and de-excitation mechanisms of rare earth doped nanocrystalline silicon and its implications for waveguide amplifier applications are investigated. Er, Nd, and Pr doped silicon rich silicon oxide (SRSO) thin films were prepared by electron cyclotron resonance enhanced chemical vapor deposition with co-sputtering of target and subsequent anneal at 950 degrees C. Temperature and pump-power dependence of Er3+ photoluminescence shows that carrier-mediated non-radiative de-excitation are strongly suppressed indicating feasibility of population inversion. Detailed investigations of dependence of Er3+ luminescence intensity and lifetime on pump width indicate that exciton-erbium coupling is dominant over carrier- exciton coupling, and that the luminescent Er ions are not inside the Si nanoclusters but in the SiO2 matrix near the clusters. Luminescence properties of Nd-doped SRSO is similar to that of Er-doped SRSO, but the temperature dependence of Nd3+ luminescence intensity is different from that of Er3+ luminescence, an effect which we ascribe to its higher transition energy. In contrast, no luminescence could be observed from Pr-doped SRSO. Erbium-doped SRSO waveguides are fabricated using the standard Si processing techniques, and guiding of 1.55 micrometers light with strong Er luminescence is observed. These results indicate that for rare erath-doped SRSO waveguides to become practical, formation of high density of small Si nanoclusters must be induced.