Joan Manel Ramírez

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

The electroluminescence (EL) at 1.54 μm of metal–oxide–semiconductor (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 Fowler–Nordheim injection threshold (above 5 MV cm(-1)) and dominates for high-field APV excitation.

Toward a 1.54

In this paper, we report on the first attempt to design, fabricate, and test an on-chip optical amplifier which works at 1540 nm and can be electrically driven. It is based on an asymmetric silicon slot waveguide which embeds the active material. This is based on erbium-doped silicon rich silicon oxide. We describe the horizontal asymmetric slot waveguide design which allows us to get a high field confinement in a nanometer thick active layer. In addition, we detail the complex process needed to fabricate the structure. The waveguides have been characterized both electrically as well as optically. Electroluminescence can be excited by hot carrier injection, due to impact excitation of the Er ions. Propagation losses have been measured and high values have been found due to processing defects. Pump and probe measurements show a voltage dependent strong attenuation of the probe signal due to free carrier accumulation and absorption in the slot waveguide region. At the maximum electrical pumping level, electroluminescence signal is in the range of tens of μW/cm 2 and the overall loss of the device is only -6 dB. Despite not demonstrating optical amplification, this study shines some light on the path to achieve an all-silicon electrically driven optical amplifier.

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High optical power density of 0.5 mW/cm2, external quantum efficiency of 0.1%, and population inversion of 7% are reported from Tb+-implanted silicon-rich silicon nitride/oxide light emitting devices. Electrical and electroluminescence mechanisms in these devices were investigated. The excitation cross section for the 543 nm Tb3+ emission was estimated under electrical pumping, resulting in a value of 8.2 × 10−14 cm2, which is one order of magnitude larger than one reported for Tb3+:SiO2 light emitting devices. These results demonstrate the potentiality of Tb+-implanted silicon nitride material for the development of integrated light sources compatible with Si technology.

m Electrically Driven Erbium-Doped Silicon Slot Waveguide and Optical Amplifier

The electrical and electroluminescence (EL) properties at room and high temperatures of oxide/ nitride/oxide (ONO)-based light emitting capacitors are studied. The ONO multidielectric layer is enriched with silicon by means of ion implantation. The exceeding silicon distribution follows a Gaussian profile with a maximum of 19%, centered close to the lower oxide/nitride interface. The electrical measurements performed at room and high temperatures allowed to unambiguously identify variable range hopping (VRH) as the dominant electrical conduction mechanism at low voltages, whereas at moderate and high voltages, a hybrid conduction formed by means of variable range hopping and space charge-limited current enhanced by Poole-Frenkel effect predominates. The EL spectra at different temperatures are also recorded, and the correlation between charge transport mechanisms and EL properties is discussed. V C 2012 American Institute of Physics .[ http://dx.doi.org/10.1063/1.4742054]

Intense green-yellow electroluminescence from Tb+-implanted silicon-rich silicon nitride/oxide light emitting devices

We report on room-temperature 1.5 lm electroluminescence from trivalent erbium (Er3þ) ions embedded in three different CMOS-compatible silicon-based hosts: SiO2, Si3N4, and SiNx. We show that although the insertion of either nitrogen or excess silicon helps enhance electrical conduction and reduce the onset voltage for electroluminescence, it drastically decreases the external quantum efficiency of Er3þ ions from 2% in SiO2 to 0.001% and 0.0004% in SiNx and Si3N4, respectively. Furthermore, we present strong evidence that hot carrier injection is significantly more efficient than defect-assisted conduction for the electrical excitation of Er3þ ions. These results suggest strategies to optimize the engineering of on-chip electrically excited silicon-based nanophotonic light sources.

Correlation between charge transport and electroluminescence properties of Si-rich oxide/nitride/oxide-based light emitting capacitors

We have fabricated a series of thin (~50 nm) erbium-doped (by ion implantation) silicon-rich oxide films in the configuration that mitigates previously proposed mechanisms for loss of light emission capability of erbium ions. By combining the methods of optical, structural and electrical analysis, we identify the erbium ion clustering as a driving mechanism to low optical performance of this material. Experimental findings in this work clearly evidence inadequacy of the commonly employed optimization procedure when optical amplification is considered. We reveal that the significantly lower erbium ion concentrations are to be used in order to fully exploit the potential of this approach and achieve net optical gain.

Electroluminescence efficiencies of erbium in silicon-based hosts

A detailed study of transport phenomena and electroluminescence of erbium-doped silicon-rich oxide/silicon oxide superlattices is presented. Extended states conduction is thermally activated from Poole-Frenkel traps located at silicon nanocrystals or its interface. These traps provide bulk limited conduction at low and medium electric fields. In contrast, under high electric fields, conduction is governed by trap-assisted tunneling of electrons from the electrode to the active layer conduction band. Superlattice electroluminescence efficiency at 1.5 μm and injected electron energy distribution in the conduction band are evaluated and compared to a silicon dioxide and a silicon-rich oxide single layer. This work sheds light on the implementation of alternative electroluminescent device architectures with strong emphasis in the hot electron engineering.

Limit to the erbium ions emission in silicon-rich oxide films by erbium ion clustering

High quantum efficiency erbium doped silicon nanocluster (Si-NC:Er) light emitting diodes (LEDs) were grown by low-pressure chemical vapor deposition (LPCVD) in a complementary metal-oxide-semiconductor (CMOS) line. Erbium (Er) excitation mechanisms under direct current (DC) and bipolar pulsed electrical injection were studied in a broad range of excitation voltages and frequencies. Under DC excitation, Fowler-Nordheim tunneling of electrons is mediated by Er-related trap states and electroluminescence originates from impact excitation of Er ions. When the bipolar pulsed electrical injection is used, the electron transport and Er excitation mechanism change. Sequential injection of electrons and holes into silicon nanoclusters takes place and nonradiative energy transfer to Er ions is observed. This mechanism occurs in a range of lower driving voltages than those observed in DC and injection frequencies higher than the Er emission rate.

Carrier transport and electroluminescence efficiency of erbium-doped silicon nanocrystal superlattices

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.

Bipolar pulsed excitation of erbium-doped nanosilicon light emitting diodes

We studied the effect of rapid thermal processing and furnace annealing on the transport properties and electroluminescence (EL) of SiO2 layers doped with Si and Er ions. The results show that for the same annealing temperature, furnace annealing decreases the electrical conductivity and increases the probability of impact excitation, which leads to an improved external quantum efficiency. Correlations between predictions from phenomenological transport models, annealing regimes and erbium EL are observed and discussed. (Some figures may appear in colour only in the online journal)