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Excitable Er fraction and quenching phenomena in Er-doped SiO2 layers containing Si nanoclusters

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This paper investigates the interaction between Si nanoclusters  Si-nc and Er in SiO2, reports on the optical
characterization and modeling of this system, and attempts to clarify its effectiveness as a gain material for
optical waveguide amplifiers at 1.54  m. Silicon-rich silicon oxide layers with an Er content of 4–6
1020 at./cm3 were deposited by reactive magnetron sputtering. The films with Si excess of 6–7 at. %, and
postannealed at 900 °C showed the best Er3+ photoluminescence  PL intensity and lifetime, and were used for
the study. The annealing duration was varied up to 60 min to engineer the size and density of Si-nc and
optimize Si-nc and Er coupling. PL investigations under resonant  488 nm and nonresonant  476 nm pumping
show that an Er effective excitation cross section is similar to that of Si-nc  10−17–10−16 cm2 at low
pumping flux  1016–1017 cm−2 s−1, while it drops at high flux  1018 cm−2 s−1. We found a maximum
fraction of excited Er of about 2% of the total Er content. This is far from the 50% needed for optical
transparency and achievement of population inversion and gain. Detrimental phenomena that cause depletion
of Er inversion, such as cooperative up conversion, excited-stated absorption, and Auger deexcitations are
modeled, and their impact in lowering the amount of excitable Er is found to be relatively small. Instead,
Auger-type short-range energy transfer from Si-nc to Er is found, with a characteristic interaction length of
0.4 nm. Based on such results, numerical and analytical  Er as a quasi-two-level system coupled rate equations
have been developed to determine the optimum conditions for Er inversion. The modeling predicts that
interaction is quenched for high photon flux and that only a small fraction of Er  0.2–2 % is excitable through
Si-nc. Hence, the low density of sensitizers  Si-nc and the short range of the interaction are the explanation of
the low fraction of Er coupled. Efficient ways to improve Er-doped Si-nc thin films for the realization of
practical optical amplifiers are also discussed.

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Reproducció digital del document publicat en format paper, proporcionada per PROLA i http://dx.doi.org/10.1103/PhysRevB.76.245308

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Articles publicats en revistes (Enginyeria Electrònica i Biomèdica)

# metadata.dc.title[].value
Excitable Er fraction and quenching phenomena in Er-doped SiO2 layers containing Si nanoclusters