Paolo Cardile

Room temperature all-silicon photonic crystal nanocavity light emitting diode at sub-bandgap wavelengths

Silicon is now firmly established as a high performance photonic material. Its only weakness is the lack of a native electrically driven light emitter that operates CW at room temperature, exhibits a narrow linewidth in the technologically important 1300-1600 nm wavelength window, is small and operates with low power consumption. Here, an electrically pumped all-silicon nano light source around 1300-1600 nm range is demonstrated at room temperature. Using hydrogen plasma treatment, nano-scale optically active defects are introduced into silicon, which then feed the photonic crystal nanocavity to enhance the electrically driven emission in a device via Purcell effect. A narrow (Δλ=0.5 nm) emission line at 1515 nm wavelength with a power density of 0.4mW/cm2 is observed, which represents the highest spectral power density ever reported from any silicon emitter. A number of possible improvements are also discussed, that make this scheme a very promising light source for optical interconnects and other important silicon photonics applications.

Concentration dependence of the Er3+ visible and infrared luminescence in Y2−xErxO3 thin films on Si

Y2−xErxO3 thin films, with x varying between 0 and 0.72, have been successfully grown on crystalline silicon (c-Si) substrates by radio-frequency magnetron cosputtering of Y2O3 and Er2O3 targets. As-deposited films are polycrystalline, showing the body-centered cubic structure of Y2O3, and show only a slight lattice parameter contraction when x is increased, owing to the insertion of Er ions. All the films exhibit intense Er-related optical emission at room temperature both in the visible and infrared regions. By studying the optical properties for different excitation conditions and for different Er contents, all the mechanisms (i.e., cross relaxations, up-conversions, and energy transfers to impurities) responsible for the photoluminescence (PL) emission have been identified, and the existence of two different well-defined Er concentration regimes has been demonstrated. In the low concentration regime (x up to 0.05, Er-doped regime), the visible PL emission reaches its highest intensity, owing to the in...

Enhanced 1.54 μm emission in Y-Er disilicate thin films on silicon photonic crystal cavities.

We introduce an Y-Er disilicate thin film deposited on top of a silicon photonic crystal cavity as a gain medium for active silicon photonic devices. Using photoluminescence analysis, we demonstrate that Er luminescence at 1.54 μm is enhanced by coupling with the cavity modes, and that the directionality of the Er optical emission can be controlled through far-field optimization of the cavity. We determine the maximum excitation power that can be coupled into the cavity to be 12 mW, which is limited by free carrier absorption and thermal heating. At maximum excitation, we observe that nearly 30% of the Er population is in the excited state, as estimated from the direct measurement of the emitted power. Finally, using time-resolved photoluminescence measurements, we determine a value of 2.3 for the Purcell factor of the system at room temperature. These results indicate that overcoating a silicon photonic nanostructure with an Er-rich dielectric layer is a promising method for achieving light emission at 1.54 µm wavelength on a silicon platform.

Electrical conduction and optical properties of doped silicon-on-insulator photonic crystals

We investigate the electrical properties of silicon-on-insulator (SOI) photonic crystals as a function of both doping level and air filling factor. The resistance trends can be clearly explained by the presence of a depletion region around the sidewalls of the holes that is caused by band pinning at the surface. To understand the trade-off between the carrier transport and the optical losses due to free electrons in the doped SOI, we also measured the resonant modes of L3 photonic crystal nanocavities and found that surprisingly high doping levels, up to 1018/cm3, are acceptable for practical devices with Q factors as high as 4×104.

Erbium―oxygen interactions in crystalline silicon

In this paper we have investigated the role of the Er–O interaction on the photoluminescence properties of Er-doped crystalline silicon. We demonstrate that the strong Er–O interaction leads to an O redistribution after thermal treatment. In particular, in the absence of Er, O out-diffuses from the Si surface and a depletion of O in the first micron below the surface is observed. In the presence of Er, the rare earth acts as a getter for O and therefore there is an O redistribution as a result of the balance between O out-diffusion and O trapping by the Er. This implies that the O concentration that remains in the Si crystal changes after thermal annealing and it is largely determined by the amount of Er present in the sample. These data will be presented and the implication on the Er optical activity discussed.

Structural and optical properties of highly Er-doped Yb-Y disilicate thin films

Highly Er-doped Yb-Y disilicates thin films grown on c-Si will be presented. The approach has permitted to vary independently the concentrations of both active rare earths, Er and Yb, and to effectively control the Er sensitization from Yb ions. We will demonstrate that these films are stable, having a uniform distribution of the chemical components throughout their thickness and a favored crystallization of the α-phase, which is the most optically efficient. We verified that this crystallization can be ascribed to a densification of the material and to the mobility locally introduced by ion implantation. Finally we will show a strong PL emission at 1.54 μm, associated to the Yb-Er energy transfer mechanism, without any deleterious energy back-transfer. These properties make this new class of thin films a valuable and promising approach for the realization of efficient planar amplifiers.

Energy transfer mechanisms in Er-Yb-Y disilicate thin films

We investigate the optical properties of Er-Yb-Y disilicate thin films in which Er and Yb contents are varied independently. From time-resolved measurements of Yb decay in absence and in presence of Er, we analyzed and modeled the energy transfer mechanism identifying all the de-excitation channels and measuring a coupling constant CYb-Eru2009=u20093.0u2009×u200910−39 cm6/s. Finally, we calculated the efficiency of Yb-Er energy transfer process and we correlated it with Er photoluminescence, demonstrating that it is controlled by the energy transfer mechanism. The maximum efficiency is found for 1.5u2009×u20091021 Er/cm3 and 1.5u2009×u20091022 Yb/cm3, by making this material very promising for optical amplifiers.

Room temperature electrically pumped silicon nano-light source at telecommunication wavelengths

We demonstrate electrically pumped silicon nano-light source at room temperature, having very narrow emission line (<0.5nm) at 1500nm wavelength, by enhancing the electroluminescence (EL) via combination of hydrogen plasma treatment and Purcell effect. The measured output power spectral density is 0.8mW/nm/cm2, which is highest ever reported value from any silicon light emitter.

Microscopic investigations of advanced thin films for photonics

We present the different approaches we recently followed to achieve intense room temperature photoluminescence (PL) from Si-based materials. On one side we obtained sub-bandgap PL from H-related defects induced by the H2 plasma treatment of Si photonic crystal (PhC) nanocavities. We demonstrated that a strong and narrow PL emission can be obtained in the PhC nanocavities due to the formation of a damaged layer mainly consisting of nanometric platelets and bubbles. An overall 40000-fold enhancement of the PL signal, with respect to pure crystalline Si, has been achieved and moreover the signal can be tuned in a wide range by only changing the PhC parameters. On the other side, we focused our attention on the properties of SiO2 and SiOC host matrices doped with Eu ions. C addition produces a strong enhancement of the Eu PL with respect to pure SiO2 films. The chemical and structural characterization of these materials reveals an extensive Eu clustering in SiO2-based films, while C addition induces a significant reduction of this phenomenon, enhancing the fraction of optically active Eu ions. These results can be applied for the realization of efficient Si-based light sources.

Er 3+ excitation and up-conversion processes in Y 2−x Er x Si 2 O 7 films for planar optical amplifiers

Structural and optical properties of Y<inf>2−x</inf>Er<inf>x</inf>Si<inf>2</inf>O<inf>7</inf> thin films have been studied. For higher Er content mechanisms related to Er-Er interactions increase optical efficiency. Moreover the influence of up-conversion has been estimated.