Preferential suppression of Auger energy backflow by separation of Er ions from carriers with a thin oxide interlayer in Er-doped porous silicon

Strong enhancement of the Er-related 1.54 μm emission was obtained at room temperature from Er-doped porous silicon (PSi), when host PSi was slightly preoxidized at 900°C before Er incorporation. It was speculated that the formation of the oxide interlayer played an important role. Separate measurements of the energy transfer and the Auger deexcitation between carriers in Si crystallites and Er ions were carried out using a two-beam (cw and pulse) excitation method for various preoxidation time which was supposed to change the oxide interlayer thicknesses from about 1 to 10 nm. It was found that a very thin SiO2 interlayer between Si crystallites and Er ions suppressed preferentially the Auger deexcitation to the carrier-mediated Er excitation. A thin SiO2 interlayer was also effective to suppress the phonon-assisted energy backtransfer at high temperatures (so-called temperature quenching). This preferential suppression of the energy backflow (both Auger deexcitation and temperature quenching) by a thin oxide interlayer led to a strong room temperature Er-related emission at 1.54 μm in Er-doped porous silicon. The Er/SiO2/Si structure was also formed on a flat Si surface and quite the same result was obtained. The oxide interlayer thickness of ∼2 nm was found optimum to suppress the energy backflow sufficiently with only a slight decrease in the carrier-mediated excitation of Er ions.