Exciton-mediated excitation of Er 3+ in Erbium-doped silicon rich silicon oxide
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Exciton-mediated excitation of Er3+ in Erbium-doped silicon rich silicon oxide Se-Young Seo and Jung H. Shin Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), 373-1 Kusung-dong, Yusung-gu, Taejon, Korea ABSTRACT Exciton-mediated excitation of Er3+ in erbium doped silicon rich silicon oxide (SRSO) is investigated. Er-doped SRSO films were fabricated by electron cyclotron-resonance plasmaenhanced chemical vapor deposition of Er-doped SiOx (x < 2) using SiH4 and O2 as source gases and co-sputtering of Er, followed by an anneal at 950 °C. Very weak visible luminescence from Si nanocluster relative to Er3+ luminescence were observed, indicating a very efficient excitation of Er3+ ions by Si nanoclusters. From detailed modeling and analysis of time-resolved Er3+ luminescence as the excitation duration and excitation power, we conclude that exciton-erbium coupling is dominant over exciton-nanocluster. The results are consistent with the proposal that the luminescent Er3+ ions are located predominantly in the SiO2 layer. INTRODUCTION Er3+ ions, when excited, can emit light at 1.54 µm, which coincides with the minimum loss window of silica-based optical fibers. Thus Er3+ has been incorporated into silica for optical applications such as Er-doped waveguide amplifiers (EDWA). In such EDWA, high excitation and luminescence efficiencies are needed for practical amplification. Recently, it was reported that in Er-doped silicon-rich silicon oxide, which is consists of Si nanoclusters embedded in a SiO2 matrix, the excitation efficiency of Er3+ is greatly enhanced due to high absorption crosssection of Si nanocrystals, which then excite the incorporated Er atoms [1-4], thereby raising the possibility of realizing Si based optoelectronics. Carrier-mediated excitation mechanism, which has been used successfully to describe excitation of Er3+ in bulk Si [5], is often used to explain the excitation of Er3+ ions in SRSO. Figure 1 shows a schematic description of such a carrier-mediated excitation mechanism. Free carriers in nanoclusters, created by incoming photons, are trapped Er-related defect states, thus
(b) cnNx
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E (a) an
I13/2
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(c) N x τ ex
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E Si nano cluster
Er related defects
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Er3+
Figure 1. Exciton-mediated excitation of Er3+ in SRSO. (a) Free carriers in Si nanoclusters, which are created in Si, form excitons at an Er-related defect state. These excitons can be de-excited by (b) free carrier Auger excitation or(c) can excite Er3+ ions.
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forming excitons (indicated by arrow labeled (a)). These excitons can be de-excited by Auger excitation of free carriers (labeled (b)), or can excite Er3+ ions (labeled (c)). While the proposed excitation mechanism is the same for both bulk Si and SRSO, there are important differences. In bulk-Si, excited Er3+ ions are de-excited non-radiatively by strong interaction with carriers, leading to very low luminescence efficiencies [5,6]. In SRSO, on the other hand, it has been shown that such carrier-media
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