Er-doped light emitting slot waveguides monolithically integrated in a silicon photonic chip.

An integrated erbium-based light emitting diode has been realized in a waveguide configuration allowing 1.54 µm light signal routing in silicon photonic circuits. This injection device is based on an asymmetric horizontal slot waveguide where the active slot material is Er(3+) in SiO2 or Er(3+) in Si-rich oxide. The active horizontal slot waveguide allows optical confinement, guiding and lateral extraction of the light for on-chip distribution. Light is then coupled through a taper section to a passive Si waveguide terminated by a grating which extracts (or inserts) the light signal for measuring purposes. We measured an optical power density in the range of tens of µW/cm(2) which follows a super-linear dependence on injected current density. When the device is biased at high current density, upon a voltage pulse (pump signal), free-carrier and space charge absorption losses become large, attenuating a probe signal by more than 60 dB/cm and thus behaving conceptually as an electro-optical modulator. The integrated device reported here is the first example, still to be optimized, of a fundamental block to realize an integrated silicon photonic circuit with monolithic integration of the light emitter.

Erbium emission in MOS light emitting devices: from energy transfer to direct impact excitation.

The electroluminescence (EL) at 1.54 µm of metal­oxide­semiconductor (MOS) devices withEr3C ions embedded in the silicon-rich silicon oxide (SRSO) layer has been investigated under different polarization conditions and compared with that of erbium doped SiO2 layers. EL time-resolved measurements allowed us to distinguish between two different excitation mechanisms responsible for the Er3C emission under an alternate pulsed voltage signal (APV). Energy transfer from silicon nanoclusters (Si-ncs) to Er3C is clearly observed at low-field APV excitation. We demonstrate that sequential electron and hole injection at the edges of the pulses creates excited states in Si-ncs which upon recombination transfer their energy to Er3C ions. On the contrary, direct impact excitation of Er3C by hot injected carriers starts at the Fowler­Nordheim injection threshold (above 5 MV cm(-1)) and dominates for high-field APV excitation.

Blue-green to near-IR switching electroluminescence from Si-rich silicon oxide/nitride bilayer structures.

Blue-green to near-IR switching electroluminescence (EL) has been achieved in a metal-oxide-semiconductor light emitting device, where the dielectric has been replaced by a Si-rich silicon oxide/nitride bilayer structure. To form Si nanostructures, the layers were implanted with Si ions at high energy, resulting in a Si excess of 19%, and subsequently annealed at 1000 °C. Transmission electron microscopy and EL studies allowed ascribing the blue-green emission to the Si nitride related defects and the near-IR band with the emission of the Si-nanoclusters embedded into the SiO(2) layer. Charge transport analysis is reported and allows for identifying the origin of this two-wavelength switching effect.

Metal-nitride-oxide-semiconductor light-emitting devices for general lighting.

The potential for application of silicon nitride-based light sources to general lighting is reported. The mechanism of current injection and transport in silicon nitride layers and silicon oxide tunnel layers is determined by electro-optical characterization of both bi- and tri-layers. It is shown that red luminescence is due to bipolar injection by direct tunneling, whereas Poole-Frenkel ionization is responsible for blue-green emission. The emission appears warm white to the eye, and the technology has potential for large-area lighting devices. A photometric study, including color rendering, color quality and luminous efficacy of radiation, measured under various AC excitation conditions, is given for a spectrum deemed promising for lighting. A correlated color temperature of 4800K was obtained using a 35% duty cycle of the AC excitation signal. Under these conditions, values for general color rendering index of 93 and luminous efficacy of radiation of 112 lm/W are demonstrated. This proof of concept demonstrates that mature silicon technology, which is extendable to low-cost, large-area lamps, can be used for general lighting purposes. Once the external quantum efficiency is improved to exceed 10%, this technique could be competitive with other energy-efficient solid-state lighting options.

Towards population inversion of electrically pumped Er ions sensitized by Si nanoclusters.

This study reports the estimation of the inverted Er fraction in a system of Er doped silicon oxide sensitized by Si nanoclusters, made by magnetron sputtering. Electroluminescence was obtained from the sensitized erbium, with a power efficiency of 10(-2)%. By estimating the density of Er ions that are in the first excited state, we find that up to 20% of the total Er concentration is inverted in the best device, which is one order of magnitude higher than that achieved by optical pumping of similar materials.

Quantum dot networks in dielectric media: from compact modeling of transport to the origin of field effect luminescence.

We present a compact model of transport through a random distribution of interacting quantum dots embedded in a dielectric matrix. The model is based on a network of interconnected tunnel junctions sandwiched between two electrodes, resulting in a system of nonlinear differential equations which is numerically solved for a given time-dependent voltage applied to the gate. The capacitance matrix, electron/hole tunneling currents and the effective area of conduction between quantum dots are calculated at each integration step. The transport properties obtained from the model are successfully validated against experimental data for a silicon nanocrystal basic MOS cell, showing its potential applicability to non-volatile memories. In addition, through a simple rate equation, the calculated charge flux tunneling or impacting the nanocrystals is converted into electroluminescence. In this regard, we discuss the origin of the recently reported field effect luminescence in silicon nanocrystals. It is found that the idea of quantum-confined exciton creation through sequential injection of opposite sign carriers is in contradiction with the model and with the electron/hole tunneling time ratio obtained through the WKB approximation due to the difference in the electron and hole potential barrier heights. We show how our model of transport, along with a rate equation with the reported value for the absorption cross section for electrical excitation of silicon nanocrystals (approximately 10(-14) cm(2)), is in good agreement with experimental data obtained under pulsed excitation, without requiring further assumptions such as the formation of excitons from hole tunneling into electron-charged nanocrystals, revealing impact excitation of electrons/holes from the same substrate as the physical origin of the observed field effect luminescence.