We have studied the current transport and electroluminescence properties of metal oxide semiconductor ͑MOS͒ devices in which the oxide layer, which is codoped with silicon nanoclusters and erbium ions, is made by magnetron sputtering. Electrical measurements have allowed us to identify a Poole-Frenkel conduction mechanism. We observe an important contribution of the Si nanoclusters to the conduction in silicon oxide films, and no evidence of Fowler-Nordheim tunneling. The results suggest that the electroluminescence of the erbium ions in these layers is generated by energy transfer from the Si nanoparticles. Finally, we report an electroluminescence power efficiency above 10 −3 %.

Photoluminescence spectroscopy and atom probe tomography were used to explore the optical activity and microstructure of Er3+-doped Si-rich SiO2 thin films fabricated by radio-frequency magnetron sputtering. The effect of post-fabrication annealing treatment on the properties of the films was investigated. The evolution of the nanoscale structure upon an annealing treatment was found to control the interrelation between the radiative recombination of the carriers via Si clusters and via 4f shell transitions in Er3+ ions. The most efficient 1.53-μm Er3+ photoluminescence was observed from the films submitted to low-temperature treatment ranging from 600°C to 900°C. An annealing treatment at 1,100°C, used often to form Si nanocrystallites, favors an intense emission in visible spectral range with the maximum peak at about 740 nm. Along with this, a drastic decrease of 1.53-μm Er3+ photoluminescence emission was detected. The atom probe results demonstrated that the clustering of Er3+ ions upon such high-temperature annealing treatment was the main reason. The diffusion parameters of Si and Er3+ ions as well as a chemical composition of different clusters were also obtained. The films annealed at 1,100°C contain pure spherical Si nanocrystallites, ErSi3O6 clusters, and free Er3+ ions embedded in SiO2 host. The mean size and the density of Si nanocrystallites were found to be 1.3± 0.3 nm and (3.1± 0.2)×1018 Si nanocrystallites·cm−3, respectively. The density of ErSi3O6 clusters was estimated to be (2.0± 0.2)×1018 clusters·cm−3, keeping about 30% of the total Er3+ amount. These Er-rich clusters had a mean radius of about 1.5 nm and demonstrated preferable formation in the vicinity of Si nanocrystallites.

Articles you may be interested inResonant structures based on amorphous silicon suboxide doped with Er 3 + with silicon nanoclusters for an efficient emission at 1550 nm J. Vac. Sci. Technol. B 27, L38 (2009) This study investigates the influence of the deposition temperature T d on the Si-mediated excitation of Er ions within silicon-rich silicon oxide layers obtained by magnetron cosputtering. For T d exceeding 200°C, an efficient indirect excitation of Er ions is observed for all as-deposited samples. The photoluminescence intensity improves gradually up to a maximum at T d = 600°C before decreasing for higher T d values. The effects of this "growth-induced annealing" are compared to those resulting from the same thermal budget used for the "classical" approach of postdeposition annealing performed after a room temperature deposition. It is demonstrated that the former approach is highly beneficial, not only in terms of saving time but also in the fourfold enhancement of the Er photoluminescence efficiency.

Series of Er-doped Si-rich silicon oxide layers were studied with the aim of optimizing the coupling between Er ions and the Si-based sensitizers. The layers were grown at substrate temperature between 400 and 600°C by the cosputtering of three confocal targets: Si, SiO2, and Er2O3. The influence of Si excess (5–15at.%) and annealing temperature (500–1100°C) was examined for two concentrations of Er ions (3.5×1020 and ∼1021cm−3). We report the first observation of significant Er photoluminescence (PL) from as-grown samples excited by a nonresonant 476nm line, with a lifetime in the range of 1.3–4ms. This suggests the occurrence of an indirect excitation of Er through Si-based entities formed during the deposition. A notable improvement was observed for both Er PL intensity and lifetime after annealing at 600°C. This temperature is lower than that required for phase separation, suggesting the formation of “atomic scale” sensitizers (Si agglomerates, for example) considered in recent work. For high Er doping (∼1021cm−3), an optimum Er PL was obtained for the sample grown at 500°C, annealed at 600°C, and containing ∼13at.% of Si excess. This high PL should correspond to an optimum fraction of coupled Er for this series, which was roughly estimated to about 11% of the total Er content for an excitation photon flux of few 1019phcm−2s−1. For the moderately Er-doped series (3.5×1020cm−3) grown at 500°C, the optimum Er PL was found for the samples containing about 9at.% silicon and annealed in the 600–900°C range. The time decay reached a value as high as 9ms for low Si excess (<6at.%) and 6–7.5ms for high values of Si excess. The fraction of Er ions coupled to sensitizers was similarly estimated for the best sample of this series and found to be as high as 22% of the total Er content.

Optical properties of directly excited erbium ͑Er 3+ ͒ ions have been studied in silicon rich silicon oxide materials codoped with Er 3+ . The spectral dependence of the direct excitation cross section ͑ dir ͒ of the Er 3+ atomic 4 I 15/2 → 4 I 11/2 transition ͑around 0.98 m͒ has been measured by time resolved -photoluminescence measurements. We have determined that dir is 9.0Ϯ 1.5 ϫ 10 −21 cm 2 at 983 nm, at least twice larger than the value determined on a stoichiometric SiO 2 matrix. This result, in combination with a measurement of the population of excited Er 3+ as a function of the pumping flux, has allowed quantifying accurately the amount of optically active Er 3+ . This concentration is, in the best of the cases, 26% of the total Er population measured by secondary ion mass spectrometry, which means that only this percentage could provide optical gain in an eventual optical amplifier based on this material.

International audienceThe structural and optical emission properties of Er-doped silicon-rich silica layers containing 10 21 at cm À3 of erbium are studied as a function of deposition conditions and annealing treatment. Magnetron co-sputtering of three confocal targets (Si, SiO 2 and Er 2 O 3) under a plasma of pure argon was used to deposit the layers at 500 1C. The silicon excess was varied in the layers in the range 7–15 at% by monitoring the power applied on Si cathode. The as-grown samples were found significantly emitting at 1.54 mm under non-resonant excitation. A maximum Er emission was observed after annealing at a moderate temperature (600 1C) for any amount of Si excess, with a highest 1.54 mm photoluminescence (PL) from the sample containing 13 at% of Si. While no nanocrystals were observed in the samples annealed at 600 1C, the sensitizers might, therefore, consist in 'atomic' scaled entities (Si agglomerates, for example) considered in recent similar work. The comparison of the emission features of our ''best'' sample and their counterparts reported so far, shows that the approach used this work allows to increase the fraction of the Er 3+ ions coupled to Si sensitizers from 3% up to 12% of the total Er content

Er-doped silicon-rich silicon oxide layers have been grown at 600 1C by magnetron co-sputtering of three confocal cathodes (Si, SiO 2 and Er 2 O 3) in pure argon plasma. The structural and optical properties of the layers were examined in the function of deposition and annealing conditions. It was shown that the increase of the RF power density applied on the Si cathode from 0.74 to 2.07 W cm À2 , while maintaining constant RF power on the two other cathodes, allows a fine engineering of the Si excess from 5 to 15 at%. The Er content was evaluated to 1 Â10 21 at cm À3. A high Er 3+ emission was observed under non-resonant (476 nm) excitation from as-deposited layers, which was significantly improved after annealing at 600 1C. The Er PL was found to be much more intense than the best samples reported so far, which was annealed at 900 1C and contains, however, lower Er content (5.4 Â 10 20 at cm À3) and Si excess (7 at% of Si). The Er emission lifetime was found to be about 6 ms for low Si excess (5 at%) and 1-2 ms for high Si excess. Upon reducing the Er content by a factor of three, the Er 3+ PL intensity was further increased and the lifetime reached 5.5 ms, suggesting a notable increase of the fraction of coupled Er ions.

The present study examines the influence of the layer thickness on the emission of Er ions coupled to Si nanoclusters within a silica matrix obtained by magnetron co‐sputtering at two typical temperatures (ambient and 500 °C. Such an investigation is essential to optimise the material for specific applications, inasmuch as thin layers of tens of nm are requested for electrically‐excited devices, while much thicker films (≥ 1 µm) are necessary for optically‐excited waveguides, lasers, etc. The Er PL was detected from as‐deposited samples with significant intensity for that grown at 500 °C. This PL improves with annealing and also with the layer thickness, up to a factor 4 when the thickness is increased from few tens to more than 1.3 µm.The origin of this behaviour seems to lie in some limiting factors related to the film thinness, such as barriers for nucleation and growth of sensitizers (Si‐ncs), stresses affecting the onset of phase separation and then the formation of Si‐ncs. To favour the growth of Si‐ncs in films as thin as tens of nm, the increase of the amount of Si excess was found to be necessary to enhance the Er PL through an increase of the density of Si‐ncs and, therefore, the coupling with Er ions. Such an enrichment with Si offers an additional advantage of favouring the injection and transport of carriers by electrical excitation (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)