In this talk we present on recent advancements in hybrid-glass waveguides on silicon photonic platforms. We describe novel monolithic hybrid integration approaches and waveguide designs for functional glass claddings on silicon-on-insulator (SOI). We describe our results on low-loss hybrid tellurite-silicon waveguides, high-Q resonators, and amplifiers and lasers and our recent efforts to optimize their performance and utility in silicon photonic systems. Such devices are promising for new functionalities in sensing, metrology, computing, and communications applications.
We describe a prototyping process for silicon nitride photonic integrated circuits, targeting applications in the visible and near-infrared wavelength ranges. The platform is based on direct-write electron beam lithography technology and provides a route toward the rapid fabrication of passive and thermo-optic active photonic devices. The fabrication turnaround time is on the order of several weeks, and critical feature sizes are demonstrated down to 100 nm which enables the fabrication of subwavelength metastructures. Two waveguiding material thicknesses have been demonstrated, 150 nm for visible light applications and 400 nm for infrared.
We demonstrate integrated distributed Bragg reflector lasers on a hybrid platform composed of silicon nitride waveguides coated with erbium-doped tellurium dioxide. The asymmetrical laser cavities are enclosed by gratings patterned on the 2.2-cm-long waveguide walls. Cavities with varying grating strengths are studied, yielding laser efficiencies up to 0.36%, a minimum lasing threshold of 13 mW, and emission wavelengths between 1530 and 1565 nm.
In this work, we report on all-silicon waveguide photodetectors utilizing surface state defects and bulk defects to sensitize the silicon to sub-bandgap light. The detectors are foundry fabricated, waveguide-integrated p-i-n junctions with post-processing consisting of HF acid exposure, ion implantation, annealing, or a combination of the three. HF exposure increases the photoresponse of the as-received detectors due to the increase in unpassivated surface states. The efficiency of surface state detection is greater than that for bulk defect detection in terms of mode overlap with the defected volumes of the silicon waveguide. Detectors in all cases have a 3dB bandwidth of 7GHz.
In-situ doping of Tb3+ ions in silicon oxides and oxynitrides deposited by electron-cyclotron-resonance plasma enhanced chemical-vapour (ECR-PECVD) has been performed. Oxygen and nitrogen gas flow rates were changed to produce a gradual substitution of oxygen by nitrogen in the host matrix. Bright green luminescence from as-deposited layers is observed by the naked eye under daylight conditions. Tbdoped nitrogen-rich samples showed a considerable photoluminescence (PL) enhancement compared to Tb-doped silicon oxides. An optimum layer composition for efficient Tb3+ excitation under non-resonant optical pumping is obtained. The combination of a low temperature treatment with bright luminescence could be instrumental for the development of light emitting devices in other platforms with more restrictive temperature requirements.
KEYWORDS: Organic light emitting diodes, Luminous efficiency, Electrons, Energy transfer, Quantum wells, Excitons, Electroluminescence, Energy efficiency, Quantum efficiency, Electron transport
We fabricated highly efficient blue organic light-emitting diodes (OLEDs) by designing differing emitting layer structures with fluorescent host and dopant materials of 4,4-bis (2,2-diphenylyinyl)-1,10-biphenyl and 9,10-bis (2-naphthyl) anthracene as host materials and 4,4’-bis (9-ethyl-3-carbazovinylene)-1,1’biphenyl (BCzVBi) as a dopant material to demonstrate electrical and optical improvements. Best enhancement in luminance and luminous efficiency were achieved by a quantum well structure in device F with 8668 cd/m 2 at 8 V and 5.16 cd/A at 103.20 mA/cm 2 , respectively. Among the blue OLED devices doped by BCzVBi, device B emits the deepest blue emission with Commission Internationale de l’É clairage coordinates of (0.157, 0.117) at 8 V.
This paper outlines the design and testing of a digital imaging system that utilizes an artificial neural network with unsupervised and supervised learning to convert streaming input (real time) image space into parameter space. The primary objective of this work is to investigate the effectiveness of using a neural network to significantly reduce the information density of streaming images so that objects can be readily identified by a limited set of primary parameters and act as an enhanced human machine interface (HMI). Many applications are envisioned including use in biomedical imaging, anomaly detection and as an assistive device for the visually impaired. A digital circuit was designed and tested using a Field Programmable Gate Array (FPGA) and an off the shelf digital camera. Our results indicate that the networks can be readily trained when subject to limited sets of objects such as the alphabet. We can also separate limited object sets with rotational and positional invariance. The results also show that limited visual fields form with only local connectivity.
In this study, we fabricated highly efficient blue organic light-emitting diodes by designing different emitting layer
structures with fluorescent host and dopant materials of 4,4-bis(2,2-diphenylyinyl)-1,10-biphenyl (DPVBi) and 9,10-
bis(2-naphthyl) anthracene (ADN) as host materials and 4,4’-bis(9-ethyl-3-carbazovinylene)-1,1’biphenyl (BCzVBi) as a
dopant material to demonstrate electrical and optical improvements. Best enhancement in luminance and luminous
efficiency were achieved by a quantum well structure and energy transfer between host and dopant materials in device F
as of 8668cd/m2 at 8V and 5.16 Cd/A at 103.20 mA/cm2 respectively. Among the blue OLED devices doped by
BCzVBi, device B emits the deepest blue emission with Commission Internationale de l’E´ clairage (CIExy) coordinates
of (0.157, 0.117) at 8V.
Electroluminescent devices based on light emission from Tb-doped SiO2 incorporated in a MOS capacitor
structure have been formed on SOI substrates. It is shown that with appropriate choice of Si film and buried oxide
thickness the SOI substrate can serve as a quarter-wave high-low-high index back reflector. Analysis predicts this back
reflector can boost total light output integrated over the Tb emission spectrum by approximately 35% compared to a bulk
substrate control device. Experimental devices using 100 nm thick PECVD SiO2 emitting layers doped with 1% Tb were
fabricated on substrates with nominal 32 and 108 nm Si film thickness (corresponding to approximately λ/4 and 3λ/4 at
the Tb emission peak). The Si films were doped to 1019 - 1020 cm-3 by As implantation. Uniform bright green
electroluminescence was obtained from 250 μm square devices, demonstrating that current crowding is not an issue even
with such a thin Si film. The comparison of output spectra for thick and thin Si films demonstrates that optical
absorption in the heavily doped Si film does not seriously degrade the light output of the devices.
In this work, we report theoretical and experimental results on the use of Cadmium Telluride (CdTe) doped with Zinc
(Zn) as core material for the development of all-optical photonic devices. We include the design of optical waveguides
for strong field confinement, technological processes to grow CdTe on 6" or 8" wafers (suitable for high-volume
manufacturing) as well as the fabrication and optical characterization of optical waveguides with a CdTe core.
Monolithic integration of silicon micro-photonic devices with silicon microelectronics presents one potential solution to the interconnect bottleneck in deep submicron CMOS microprocessors. However, an inability to develop a robust silicon based electroluminescent (EL) technology continues to severely limit the feasibility of such a structure. Despite its promising photoluminescent (PL) properties, the erbium doped silicon rich silicon oxide material system has been only partly successful in EL devices owing to dielectric breakdown resulting from high field excitation requirements. However, PL data indicate that quantum confinement effects in this system enable it to overcome many of the luminescence quenching properties of bulk silicon based materials, while simultaneously offering the structural and chemical resilience which luminescent forms of silicon (eg. porous silicon) lack. However, it is now clear that the resolution of the current injection problem will require a detailed understanding of all known and especially potential luminescence excitation mechanisms. The present study compares PL measurements made for SiOx:Er (x less than or equal to 2) thin films grown by electron cyclotron resonance plasma enhanced chemical vapour deposition. Various compositions, containing erbium concentration below 1 atomic %, have been annealed over a range of temperatures between 600-1100 °C. The presence of excess silicon relative to SiO2 is found to result in a 100 fold increase of the PL emission near 1540 nm, resulting from the 4I13/2 to 4I15/2 transition of the trivalent erbium ion, relative to a sample containing no silicon excess. It has been found that luminescent silicon nano-clusters can be formed throughout the range of anneal temperatures studied. A dense array of extremely small amorphous silicon clusters is found to result in an optimized sensitization of the PL at 1540 nm for annealing at 800°C. It is proposed that in some cases, silicon nano-clusters coupled to erbium ions do not emit their intrinsic luminescence. Various oxygen-based luminescent defects are identified in this study, and they seem to exhibit a coupling to silicon nano-cluster and erbium-related centres. Possible application of these films to recently developed field-effect EL devices is discussed.
The development of monolithically integrated optoelectronics in silicon has been hindered to date primarily because of silicon's inefficient optical emission properties. Recently, however, nanostructured systems exploiting quantum confinement effects have shown the potential to circumvent this problem. In this study, silicon-rich silicon oxide (SiOx, x<2) thin films doped with erbium have been deposited on silicon substrates by electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD). The formation of silicon nanoclusters along with optically active erbium ion complexes during high temperature annealing results in strong erbium photoluminescence near a wavelength of 1.54 μm. A portion of the deposition parameter space for the ECR-PECVD system has been mapped in an attempt to optimize the films for this luminescence. The resulting films ranged in composition from 0% to 22% excess silicon and 0.45% to 3.7% erbium, as determined by Rutherford Backscattering Spectroscopy. The effects of annealing were investigated between 600 oC and 1000 oC under flowing nitrogen gas. The 1.54μm emission was found to be enhanced by the presence of excess silicon, reaching a maximum at ~5-8 atomic % excess and an 800 oC anneal. This result strongly suggests the sensitization of infrared, erbium luminescence by silicon nanoclusters. The films exhibited an additional blueviolet light emission which has also been attributed to the erbium dopant. The visible and infrared luminescence signals were found to occur in inverse proportion to each other with the visible signal decreasing as the amount of silicon excess increases.
Cadmium Telluride (CdTe) is a well known photonic material in the fields of infrared imaging and solar cells. Its nonlinear optical properties also make it a promising candidate for novel telecom applications that would utilize its high Kerr coefficient to produce advanced logical devices such as switches, routers and wavelength converters. The large photorefractive effect observed in CdTe also makes possible high-speed devices suitable for optical data processing. In order to advance such photorefractive waveguide applications, we have deposited CdTe films on silicon substrates with a native oxide layer using the pulsed laser deposition technique (PLD). Silicon was chosen as the substrate material as it is suitable for the monolithic integration of logical devices. Maintaining an oxide layer was deemed necessary as a high refractive index mismatch is desirable for high-index contrast waveguide based applications and such an index mismatch could be provided by a reasonably thick layer of SiO2. Films exhibiting some structural deficiencies, but with high optical quality were deposited through the optimization of the growth parameters. X-ray diffraction data indicates that the films are [111] oriented with rocking curves of substantial width. Atomic force microscopy images confirm that the films have a smooth surface morphology as was suggested by their mirror-like appearance. Using the optimum growth conditions, CdTe films doped with germanium were also deposited as this dopant introduces deep donor levels that enhance the photorefractive effect. A comparison of the optical properties obtained from the doped and undoped films indicate that impurities can have a marked effect on the index of refraction and extinction coefficient. Such alterations to the optical constants must be considered in the design of waveguide structures.
Silicon rich silicon oxide thin films have been fabricated by electron cyclotron resonance plasma enhanced chemical vapor deposition. Following their deposition, these films were subjected to thermal anneals at temperatures up to 1100°C for times of up to 120 minutes. Annealing of the films causes a phase separation of the material to form Si precipitates, which nucleate to form Si nanocrystals, within an amorphous SiO2 matrix. The nucleation of the nanocrystals was analyzed as a function of the composition of the films, as determined by Rutherford backscattering and elastic recoil detection analysis experiments, and the annealing conditions. The bonding structure of the films was analyzed using Fourier transform infrared spectroscopy. Surface morphology, including analysis of the size and distribution of the nanocrystals, was determined through the use of atomic force microscopy. Spectroscopic ellipsometry, in the range from 600 to 1100 nm, was used to examine the effects of the formation of nanocrystals on the optical properties, i.e., index of refraction and extinction coefficient, of the films. Photoluminescence spectra were used to show that due to quantum confinement effects the nanocrystals
exhibit luminescence, making them a potential candidate for integrated photonic emitters.
This paper describes work investigating the impact of lattice defects on the attenuation of optical signals at wavelengths
around 1550nm in silicon rib waveguides. Using Fourier transform infrared spectroscopy it is shown that high energy proton irradiation of silicon induces excess optical absorption peaked at a wavelength of 1800nm, but extending below 1600nm. This absorption is related to the introduction of silicon divacancy defects. It is further demonstrated that silicon divacancy concentration is accurately determined for a range of proton doses using positron annihilation spectroscopy and successfully predicted using an analytical expression proposed previously. Low loss rib waveguides
were fabricated in silicon-on-insulator substrates. These waveguides were subsequently implanted with silicon ions at an energy of 2.8MeV through photolithographically defined mask windows of various lengths. The additional optical loss as a result of the defects introduced by the implantation process was accurately determined. For a dose of 2.5x1014cm-2, the loss is greater than 500dBcm-1. Finally, it is shown that excess absorption can be predicted using the same analytical expression for the determination of vacancy concentration, thus providing a straightforward method for the design of integrated, on-chip optical absorbers in silicon photonic circuits.
Ivoil Koutzarov, Harry Ruda, Chandima Edirisinghe, Lech Jedral, Qiang Liu, Alan Moore, Richard Henderson, Marcel Boudreau, Mohamed Boumerzoug, Peter Mascher
We report on passivation of AlxGa1-xAs/GaAs surfaces using different sulfur and chlorine based treatments: These include ammonium sulfide solution, arsenic sulfide vapor and hydrochloric acid treatments. Enhancements in the intensity of near band-gap photoluminescence (PL) peaks, coupled with peak half-width reduction on treatment were attributed to a reduction in the density of surface states. Pre-etching using sulfuric acid- and ammonium hydroxide-based solutions prior to sulfur passivation was also found to contribute significantly to the overall success of a passivation treatment. The best sulfur-passivation results for all x (0 < x < 0.38) were found when sulfuric acid-peroxide-deionized water (Caros) solution pre-etching was followed by ammonium sulfide solution treatment at 65 degree(s)C for 25 min.
The deposition of TiN on a silicon substrate in a Triode Ion Plating (TIP) deposition system was investigated. The effects of the deposition parameters such as the pressure, electron beam current and the gas flow rates were studied by looking at the optical emission lines collected through an Optical Emission Spectrometer (OES). Two kinds of spectra were recorded: Scan spectra between 200 and 600 nm for the identification of the species in the plasma and time based spectra for monitoring the titanium and nitrogen emission lines. The deposition rate was also monitored in situ by using a crystal thickness monitor. Secondary Ion Mass Spectrometry (SIMS) profiling was used to analyse the distribution of Ti and N in the deposited films. It was found that OES can be used for the in situ monitoring of the deposition process. Moreover, the titanium emission line at 364.2 nm can be used to correct the fluctuation in the titanium evaporation rate.
The excitation processes in a DC glow discharge ignited using a saddle-field electrode configuration have been examined using optical emission spectroscopy (OES) for discharges established in SiH4, and in Ar/SiH4 and N2/SiH4 gas mixtures. The emission intensities of excited gas-phase species are correlated with plasma probe mass and energy spectral analysis of the resulting reactive radicals impinging onto the substrate holder. Discharges ignited in SiH4 exhibit strong Si optical emission lines relative to the SiH lines, reflecting extensive gas-phase decomposition of the starting SiH4. The corresponding mass spectra of positively charged radicals exhibit a dominant peak at 28 amu that is associated with Si+. The resulting deposition rate of a-Si:H scales linearly with the flow rate of SiH4. The addition of argon to the glow discharge in SiH4 assists the gas-phase dissociation of the SiH4 as indicated by higher partial pressures at 28 and 29 amu, corresponding to the enhanced formation of Si and SiH. Moreover, gas-phase interactions with excited argon result in greater excitation of the background H2, leading to a higher concentration of atomic hydrogen in the discharge. Ionized atomic hydrogen dominates the discharge current at higher Ar to SiH4 gas flow ratios. OES spectra of DC saddle-field discharges in N2/SiH4 gas mixtures indicate strong activation of N2+ and good dissociation of the SiH4 over a wide range in flow ratios, facilitating the preparation of Si:N:H films with stoichiometries ranging from N/Si = 0 to 1.8.
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