Owing to their direct band gaps, (Si)GeSn all-group-IV alloys are promising candidates for light sources, photodetectors and modulators monolithically integrated onto a CMOS-compatible mid-infrared photonic platform. Several research teams have demonstrated optically pumped GeSn lasers, and, more recently, an electrically pumped GeSn laser at low operating temperature. Here, we studied Ge0.85Sn0.15-based light emitting diodes (LEDs) and photodiodes (PDs) operating at room temperature. The stack was grown on a p-doped Ge strain-relaxed buffer at low growth temperatures (below 350°C) in a 200 mm chemical vapor deposition tool. Fabricated GeSn devices were characterized at room temperature with a Fourier-transform infrared spectrometer (FTIR) and an InSb detector. The spectral response of the FTIR InSb detector was calibrated with respect to a Deuterated Triglycine Sulfate detector (DTGS). This spectral response was then used to correct Ge0.85Sn0.15 LEDs emission spectra with emission maximum at 3.3 μm. The cutoff wavelength at 3.7 μm of the GeSn photodiode was finally obtained (at 0V bias) after correction of the Globar incident light spectrum. Such emission and detection open up promising perspectives for all-group-IV LEDs and PDs in applications such as gas sensing.
We present an innovative optical particulate matter sensor. This optical sensor ‘on-a-chip’ combines a visible fibered light source and a custom-made CMOS image sensor chip. By illuminating a single particle in an air channel, we can record the light scattering signature on the photodiode matrix. A piece realized in 3D printing achieves fiber alignment and an efficient stray light protection.
A specific scattering pattern occurs from the interaction of light with a single particle. Unlike traditional optical PM sensors based on a single photodiode detection, we measure a lens-free projection of the scattering signature on the nearby image sensor (1.5mm projection distance). This allows us to count particles and determine their size and refractive index. These parameters are retrieved through image processing and by comparison with a radiometric model that calculates the projection of a Lorenz-Mie’s scattering pattern.
We describe the sensing technique, the architecture and fabrication of this sensor as well as the characterization results, which are in good agreement with our theory-based predictions. In particular, we show that it is possible to differentiate calibrated particulates of different sizes (monodisperse polystyrene-latex spheres). The sensor is sensitive enough to detect single particle and smallest than 1μm.
We present several integrated technologies on Silicon, from visible to mid-infrared, for particulate matter and gas detection. We present new concepts to detect in the visible particulate matter with a high sensitivity and a discrimination of both particle sizes and refractive indices. For gas detection, mid-infrared technologies developments include on one hand, microhotplate thermal emitters, as a cheap solution for gas sensing, eventually enhanced by plasmonics, and on the other hand quantum cascade lasers-based photoacoustic sensors, for high precision measurement, and for which the integration on Silicon is pushed forward for a reduction of costs.
The Mid-IR spectral range (2.5 μm up to 12 μm) has been considered as the paradigm for innovative silicon photonic devices. In less than a decade, chemical sensing has become a key application for Mid-IR silicon photonic devices because of the growing potential in spectroscopy, materials processing, chemical and biomolecular sensing, security and industry applications. Measuring in this spectral range, usually called molecule fingerprint region, allows to address a unique combination of fundamental absorption bands orders of magnitude stronger than overtone and combination bands in the near IR. This feature provides highly selective, sensitive and unequivocal identification of the chemicals.
Progress in Cascade Laser technology (QCL and ICL) allows to select emission wavelengths suitable to target the detection of specific chemicals. With these sources, novel spectroscopic tools allowing real-time in-situ detection of gasses down to traces are nowadays commercially available.
Mid-IR Si photonics has developed a novel class of integrated components leading to the integration at chip level of the main building blocks required for chemical sensing, i.e. the source, the PICs and the detector. Three main directions of improvement can be drawn: i) extend the range of wavelengths available from a single source, ii) move beam handling and routing from discrete optics to PICs and iii) investigate detection schemes for a fully integrated on-chip sensing.
This paper reviews recent key achievements in the miniaturization and the co-integration of photonics devices at chip and packaging level to address cost, size and power consumption. Perspectives on potential applications will also be presented.
With the recent progress in integrated silicon photonics technology and the recent development of efficient quantum cascade laser technology (QCL), there is now a very good opportunity to investigate new gas sensors offering both very high sensitivity, high selectivity (multi-gas sensing, atmosphere analysis) and low cost thanks to the integration on planar substrate. In this context, we have developed singlemode optical waveguides in the mid-infrared based on Silicon/Germanium alloy integrated on silicon. These waveguides, compatible with standard microelectronic technologies present very low loss in the 3300 – 1300 cm-1 range. This paper presents the design, technological realization, and characterization of array waveguide grating devices specifically developed for the simultaneous detection of several gas using arrays of QCL sources. Gas sensing generally requires a tunable source continuously covering the whole operational range of the QCL stack. With this objective, specific design has been adopted to flatten the optical transfer function of the whole multiplexers. Samples devices around 2235cm-1 were realized and tested and showed results in good agreement with the modeling, flat transmission over a full 100 cm-1 operational range were obtained with a peak-to-valley modulation of -5dB were experimentally measured. These devices will be soon associated with QCL arrays in order to provide integrated, powerful, multi wavelength, laser sources in the 2235 cm-1 region applicable to NO, CO, and CO2 multi-gas sensor.
The potential of spectroscopic Mueller polarimetry for the dimensional characterization of periodic structures has already been discussed in several instances. With respect to standard scatterometry; the added value of the technique is related to the information contained in the 16 elements of the Mueller matrix, while usual scatterometry provides only two. The additional information can prove useful to decorrelate dimensional or optical parameters, and to assess the adequacy of the model describing the profiles to be reconstructed: if the model is adequate, the optimal values of the dimensional parameters must remain stable when the measurement conditions, and thus the input data, are varied.
This issue has been addressed for a series of 1D gratings etched in bulk Si and characterized by a spectroscopic polarimeter operating in the visible (Horiba Jobin Yvon MM-16), as well as CD-SEM and state-of-the art CD-AFM. With the usual lamellar or trapezoidal models both the CD and thickness values exhibit up to 10 nm systematic variations with measurement conditions. In contrast, with an original model taking into account the non-flatness of the open areas between adjacent lines the parameters become consistent to within 2 nm, well below typical tool-to-tool offsets. The corresponding profiles are also compatible with the CD-AFM images.
Spectroscopic Mueller polarimetry may provide a useful alternative to standard spectroscopic ellipsometry (SE) for the
dimensional characterization of periodic structures, as it provides 16 quantities instead of 2 for SE. We present a detailed
experimental comparison of the results provided by conventional scatterometry (0.7 - 5 eV) spectral range), Mueller
polarimetry in the visible (450 - 825 nm), electron microscopy (top CD-SEM and cross section) and state-of-the-art CDAFM
(Veeco X3D). This last instrument was considered as the best reference currently available. The samples were 1D
gratings etched in bulk Si, with 150 and 250 nm nominal CDs and several pitches for each CD. SE spectra were taken at
zero azimuthal angles (i.e. with the grooves perpendicular to the incidence plane), as it is usually done with standard
scatterometers, while Mueller spectra were measured at all azimuths in steps of 5°, allowing significant consistency tests
by comparing the results of the corresponding fits. Both techniques provided CD values in agreement with AFM and
CD-SEM data to within 5 nm, comparable to the AFM precision. Grating thickness and sidewall angle (SWA) were best
determined by Mueller polarimetry at 90° azimuth, while in the usual zero azimuth configuration, SWA was typically
underestimated by several degrees.
Sub-50 nm half pitch critical dimension metrology of resist lines by a fast goniometric scatterometry technique
in the visible range has been investigated. The goniometric optical instrumentation allows illumination and
reflection of patterned objects from almost all angles of view (0°/80° polar angles, and 0°/360° azimuthal
angles) simultaneously. Applied to scatterometry, this tomography-like technique ensures a robust lines profiles
reconstruction. Sensitivity and correlation analysis show that this technique exhibits at least equal performances
compared to ellipsometry. Since the technique uses a single wavelength, no spurious assumptions about the
refractive index of the materials illuminated is introduced is the modeling process. So the technique is believed
to be more robust than ellipsometry. We present a demonstration of CD measurement with this technique on
30 nm CD resist lines with various pitches. The results are compared to CDSEM.
We present an innovating method to measure the overlay by scatterometry using an optical Fourier transform (OFT) based system. In order to measure the overlay of patterned layers α and β, one line grating is placed in layer α and another in layer β. The two gratings have the same pitch and their lines are parallel. The whole scattering pattern of the double grating structure is then measured at fixed wavelength in a large range of incidence (0 to 80°) and for all the azimuth angles. This measurement is very rapid thanks to the OFT and not sensitive to vibration. The main advantage of OFT compared to standard OCD techniques like normal incidence reflectometry or spectroscopic ellipsometry is that the scattering pattern is more sensitive to overlay at an azimuth depending on the pitch value which is never parallel or perpendicular to the grooves of the gratings. In addition, the optical response is also sensitive to the sign of the overlay in addition to its amplitude. In a second method, we propose to measure the overlay simultaneously along the two directions of the plane using two bi-periodic structures patterned in layer α and β. By using OFT it is possible to deduce directly from the whole diffracted pattern, the overlay signs and amplitudes along both directions of the plane. The paper presents some simulations and some experimental results to illustrate this new method.
In the field of laser-induced surface damage, it has been shown that localized re-fusion of silica can be used as a mean to mitigate the damage and therefore stop its growth before the use of the optical component is impaired. In this paper, this localized re-fusion was produced using a continuous CO2 laser. As the damage is reshaped, we observed that a ring of evaporated silica is systematically deposited around the mitigated damage. This evaporated silica is likely to be non-stoechiometric and therefore to present absorption and luminescence properties.
Thus we decided to perform photoluminescence measurements in order to analyse the mitigated damages. We performed fluorescence imaging and spectroscopy using 351nm continuous laser excitation. Different experimental conditions were used for the re-fusion process and the consequences on the photoluminescence properties were studied. We also compared these properties to the properties of non-mitigated damages.
In the present paper, we use a new photo goniometric method capable to measure the entire diffracted pattern of a sub micron grating at fixed wavelength very rapidly. The complete reflectance pattern is obtained versus incidence angle (0-80°) and azimuth angle (0-360°). Regression software based on RCWA simulations has been developed. It is used to adjust automatically the grating profile with an unprecedented rapidity. Regressions have been applied to our polarimetric measurements versus incidence angle θ and versus azimuth angle φ. Results are compared to those provided by spectroscopic ellipsometry (SE) and scanning electron microscopy (SEM). We show that fixed incidence angle specular reflection coefficients versus azimuth angle R(φ) curves are very sensitive to the profiles especially when the CD is reduced mainly because of the occurrence of diffracted orders matching the CD at given azimuths even if the wavelength is much larger than the CD. Mid space illumination measurements in a large angular aperture (0<θ<80° and 0<φ<180°) can be also used to deduce profile information. We show that specular reflection coefficients can be fitted in the entire angular aperture to provide precise structural shapes. Out of specular contribution which is measured simultaneously can also be used in the analysis. We show that it is more sensitive to the grating imperfections than the specular contribution.
We present an innovating method to measure simultaneously the specular and non specular diffraction pattern of sub-micronic periodic structures. The sample is illuminated at fixed wavelength in the visible range (green laser) versus a large angular aperture both in incidence (0 to 80°) and azimuth (0 to 180°). A special optical setup including Fourier optics and a CCD camera allows to measure the entire diffraction pattern. The measurement spot size can be reduced to less than 50μm and its position can be visualized directly with the same optical setup. Polarimetric measurements can be made in less than two seconds. This new system is presented in details and the accuracy of the measurement is tested on homogeneous reference SiO2/Si samples. Then the system is applied to submicron gratings. We show that fixed incidence angle measurements are useful to visualize the specular and non specular order. So, the periodicity of the can be extracted directly. In addition the specular and non specular intensity can be used to extract more accurately the topology of the samples. We show that specular reflection versus azimuth angle can provide similar results than conventional techniques. First experimental results on bi-periodic structures are also shown.
Over the past years, DNA-chip technology has exploded. Yet
scientists using such devices have to face many problems. One of
them, due to the very low concentration of biological species to
be detected, is the weakness of fluorescence signal collected
through the reading system (microscope or scanner). To solve this
problem, we proposed to use optical thin films technology. We
studied the potentialities of this method step by step. The first
step was to be able to understand, explain and forecast the
fluorescence emitted by a DNA-chip in terms of fluorescence
angular patterns. A theoretical and experimental study enabled us
to master this issue even in the case of multi-layers substrates.
Using this knowledge we were then able to explain, through
simulations, the potentialities of this new type of substrates in
terms of fluorescence enhancement. Thus we showed that a
theoretical enhancement of twenty-fold (compare to a glass
substrate) was achievable.
Quantifying hybridization and therefore fluorescence signals has become a key-issue in DNA-chip technology. Thus a better understanding of fluorescence near a surface has become a necessity. To study this issue, we modeled the fluorophore after an electromagnetic dipole radiating over the substrate; we then developed a simulation code which enabled us to calculate the observation-angle-dependent-intensity radiated by a population and altitude. In the mean time we developed a polarized-gonio-fluoimeter which permits angular fluorescence patterns and fluorescence polarization measurements. We studied DNA-chips obtained by covalent grafting of labeled oligonucleotides. Simulation curves perfectly matched experimental ones, enabling an accurate determination of fluorophore localization on the substrate. Once achieved a better understanding of the fluorophore emission, we designed and realized a thin-film-coated microscope slide dedicated to the enhancement of DNA-chip fluorescence. This substrate was used in a c-DNA gene analysis. Fluorescence enhancement was clearly observed enabling the detection of Cart1 and P2A which are undetectable when using non-coated microscope slides.
KEYWORDS: Atomic force microscopy, Luminescence, Near field, Photons, Near field optics, Near field scanning optical microscopy, Microscopes, Photodetectors, Optical amplifiers, Sensors
We describe a near-field apertureless fluorescence microscope, capable of imaging fluorescent latex beads with subwavelength precision. The instrument is based on a home- built tapping-mode atomic-force microscope, to which an inverted optical microscope was added. The fact that the wavelength of the fluorescence that we observe is different from the wavelength of the illumination allows for a relatively straightforward detection mechanism. Sample images are presented, along with evidence that the observe effect is of optical origin.
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