We present a novel optical sensor platform designed for the detection of medical biomarkers. The sensor operates by utilizing reflection variation resulting from the modification of Fano resonance conditions. By fabricating one- and two-dimensional subwavelength quasi-periodic structures made of polymer and coated with an inorganic layer, we enable the functionality of the sensor, ultimately leading to increased sensitivity and detection threshold. The development of the sensor’s platform involves a multi-step process. The detection mechanism primarily relies on the optical response of the biosensor. The presence of analytes induces a spectral shift of the Fano resonance, which is caused by the modification of the biolayer thickness. This optical sensor platform holds significant potential for the detection of a variety of medical biomarkers, including analytes related to various pathogenes, cancer biomarkers, and others.
Fast and non-invasive screening test based on electrochemical detection of structural proteins of SARS-CoV-2 was developed. The measurement being the basis of the test is carried out in a standard three-electrode system, in which the working electrode is covered by bioreceptors immobilized on its surface by durable covalent bonding, ensuring specificity of the detection of desired analyte present in the sample. The carried out measurements allowed for detection of given protein of SARS-CoV-2 in standardized buffered samples and in samples containing virus-like particles. The estimated detection limit of the biosensor does not exceed 10^5 copies of the virus per milliliter.
We present a fibre optic biosensor for SARS-CoV-2 detection based on the lossy-mode-resonance (LMR) [6] effect, generated in a single-mode fibre with a thinned cladding and coated by thin-film dielectric with appropriately selected optical properties and thickness. The detection of selected viral structural proteins in the tested sample is ensured by specific bioreceptors. As a result of the interaction with the SARS-CoV-2 antigen, optical response in the short-wave-IR range is observed, and the detection limit does not exceed 1.3*10^2 copies/ml, when converted to the viral load concentration - sufficiently for virus detection even in the first days after infection.
Normally-off AlGaN/GaN HEMTs with p-GaN-gate, which offer high drain current and low on-state resistance at high threshold voltage and breakdown voltage values above 600V, are particularly attractive for high-power electronics applications. In this work we present the results of development of high power normally-off p-GaN gate AlGaN/GaN high electron mobility transistors carried out at Łukasiewicz Research Network-Institute of Microelectronics and Photonics. We have developed key technological steps i.e. selective etching of p-GaN layers over AlGaN, deposition of proper passivation layer as well as thermally stable isolation of adjacent devices using selective Fe+ ion implantation, which were integrated in the process flow of manufacturing of high power transistors. Finally we have shown measurements of developed normally-off p-GaN gate AlGaN/GaN HEMT power transistors assembled using in-house developed process in TO-220 package.
AlGaN/GaN High Electron Mobility Transistors (HEMTs) are capable of achieving high breakdown voltage, low operating resistance and large switching speed due to the excellent performance shown by III-N structures. The paper presents selected details of technological experimental work on high voltage (HV) AlGaN/GaN-on-Si HEMTs fabricated with multifinger structures and gate widths of up to 40×1 mm. The electrical isolation of individual devices was elaborated using Al+ implantation. The ions were implanted up to a depth of 200 nm in order to produce an effective damage and isolation up to the non-conducting AlGaN buffer layer. The influence of the ion energy (in the range 208-385 kV) and the ion dose (in the range 8.5x1012-1.4x1013cm-2) on the effectiveness of the fabricated isolation was found. The properties of the fabricated ohmic contacts (using Ti/Al/Mo/Au and Ti/Al/TiN/Cu metallization schemes) with emphasis put on the technology of recess etching were studied. The impact of various pretreatment, applied before deposition of the gate metallization, on electrical parameters of multifinger devices was analysed. The tested pretreatment methods included oxide removal in HCl-based solution, and O2 or BCl3 plasma treatment, with the lowest gate leakage current obtained for the latter. The results of fabrication of the HV HEMTs with single field-plate structures with various dielectrics (Si3N4 or Al2O3) are discussed. The characterization results within the paper cover electrical (I-V characteristics), structural (TEM, XRD), topographical (AFM) and elemental (EDS mapping) analyses.
This work was supported by The National Centre for Research and Development under Agreement nr TECHMATSTRATEG1/346922/4/NCBR/2017 for project "Technologies of semiconductor materials for high power and high frequency electronics"
Novel optical sensors the most often require thin films or surface structures with strictly controlled properties, playing a critical role in them by initiating or modifying their sensorial responses. Selected results of research on atomic layer deposited (ALD) metallic oxides will be shown, regarding their applicability for thin functional coatings in lossy mode resonance (LMR) and long period grating (LPG) optical fiber sensors. Basically amorphous films of tantalum oxide (TaxOy), zirconium oxide (ZrxOy) and hafnium oxide (HfxOy) below 200 nm were deposited at relatively low temperature (LT) of 100°C. The optical, structural, topographical, tribological, hydrophilic and chemical stability properties of the films and their technological controllability were analysed. The TaxOy was selected and successfully applied as an oxide coating in LPG sensor. As chemically robust in alkali environment (pH over 9) it allowed to gain a potential for fabrication of regenerable/reusable biosensor. Additionally, ALD technique was tested as a tool for tailoring sensorial properties of LMR sensors. The double-layer coatings composed of two different materials were experimentally tested for the first time; the coatings were composed of plasma-enhanced chemical vapour deposited (PECVD) silicon nitride (SixNy) followed by much thinner ALD TaxOy. That approach yielded operating devices, ensuring fast overlay fabrication and easy tuning of the resonant wavelength at the same time. The LT ALD TaxOy films turned out to be slightly overstoichiometric (y/x approx. 2.75). Therefore, the issue of TaxOy chemical composition was studied by secondary ion mass spectroscopy, Rutherford backscattering spectrometry and x-ray photoelectron spectrometry.
Fabrication of approx. 3 THz Al0.15Ga0.85As/GaAs QCLs grown by Molecular Beam Epitaxy equipped with Ta/Cu or Ti/Cu waveguide claddings will be presented.
Our previous studies showed that copper layers as the waveguide claddings are most promising in THz QCLs technology. The theoretical predictions showed that lasers with Ti/Cu or Ta/Cu claddings (where Ti and Ta play the role of diffusion barriers and improve adhesion) show the smallest waveguide losses when compared with other metals. The main important issue of the presentation will be the wafer bonding of the QCL active region and GaAs receptor wafer. We will compare the results of ex-situ and in-situ bonding technology. The structures were tested by optical microscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDXS). Our studies show that it was necessary to apply at least 5 nm-thick diffusion-barrier layers, as well as to keep all of the process temperatures below 400C in order to ensure the barrier tightness. The next important issue was control of composition of metallic claddings, in order to provide the control of the refractive index profiles of the claddings.
The ridge structure lasers were fabricated with ridge width in the range 100 – 140 µm, formed by dry plasma etching in BCl3/Cl2/Ar mixture in ICP RIE system.
The lasers operated with threshold current densities of approx. 1.2 kA/cm2 at 77 K and the Tmax = 130 K, when fed by 100-300 ns current pulses supplied with 0.3-1 kHz repetition frequencies.
*This research is supported by The National Centre for Research and Development (bilateral cooperation, project no. 1/POLTUR-1/2016) and TUBITAK (Scientific and Technical Research Council of Turkey) project number 215E113.
Conditions of fabrication of first-order distributed-feedback surface gratings designed for single-mode Al0.45Ga0.55As/GaAs quantum cascades lasers with the emission wavelength of about 10 μm are presented. The 1-μm-deep rectangular-shaped gratings with the period of about 1.55 μm and duty cycle in the range of 65% to 71% made by the standard photolithography are demonstrated. The wavenumber difference of about 7 cm−1 at 77 K is observed for the radiation emitted by lasers fabricated from the same epitaxial structure with ridge widths in the range of 15 to 25 μm. Moreover, the emission wavelength of the lasers could be tuned with temperature at a rate of 1 nm/K in the temperature range of 77 to 120 K. The full width at half maximum of the emitted spectra is ∼0.4 cm−1.
Conditions of fabrication of first order distributed-feedback surface gratings designed for single-mode Al0.45Ga0.55As/GaAs quantum cascades lasers with the emission wavelength of about 10μm are presented. The 1 μm-deep rectangular-shaped gratings with the period of about 1.55 μm and duty cycle in the range of 65-71% made by the standard photolithography are demonstrated. The wavenumber difference of about 7 cm-1 at 77 K is observed for the radiation emitted by lasers fabricated from the same epitaxial structure with ridge widths in the range of 15-25 μm. Moreover, the emission wavelength of the lasers could be tuned with temperature at a rate of 1 nm/K in the temperature range of 77-120 K. The full width at half maximum of the emitted spectra is ~ 0.4 cm-1.
We report research results with regard to AlGaAs/GaAs structure processing for THz quantum-cascade lasers (QCLs). We focus on the processes of Ti/Au cladding fabrication for metal–metal waveguides and wafer bonding with indium solder. Particular emphasis is placed on optimization of technological parameters for the said processes that result in working devices. A wide range of technological parameters was studied using test structures and the analysis of their electrical, optical, chemical, and mechanical properties performed by electron microscopic techniques, energy dispersive x-ray spectrometry, secondary ion mass spectroscopy, atomic force microscopy, Fourier-transform infrared spectroscopy, and circular transmission line method. On that basis, a set of technological parameters was selected for the fabrication of devices lasing at a maximum temperature of 130 K from AlGaAs/GaAs structures grown by means of molecular beam epitaxy. Their resulting threshold-current densities were on a level of 1.5 kA/cm2. Furthermore, initial stage research regarding fabrication of Cu-based claddings is reported as these are theoretically more promising than the Au-based ones with regard to low-loss waveguide fabrication for THz QCLs.
We report our research on processing of AlGaAs/GaAs structures for THz quantum-cascade lasers (QCLs). We focus on
the processes of fabrication of Ti/Au claddings for metal-metal waveguides and the wafer bonding with indium solder.
We place special emphasis on the optimum technological conditions of these processes, leading to working devices. The
wide range of technological conditions was studied, by use of test structures and analyses of their electrical, optical,
chemical and mechanical properties, performed by electron microscopic techniques, energy dispersive X-ray
spectrometry, secondary ion mass spectroscopy, atomic force microscopy, fourier-transform infra-red spectroscopy and
circular transmission line method. On the basis of research a set of technological conditions was selected, and devices
lasing at the maximum temperature 130K were fabricated from AlGaAs/GaAs structures grown by molecular beam
epitaxy (MBE) technique. Their threshold-current densities were about 1.5kA/cm2. Additionally we report our initial
stage research on fabrication of Cu-based claddings, that theoretically are more promising than the Au-based ones for
fabrication of low-lossy waveguides for THz QCLs.
Quantum cascade lasers (QCL’s) have proven their usefulness as light sources in many applications, like remote gas
sensing, molecular spectroscopy or free-space communication. In most cases the high-quality low-divergence beam is
desired. This work presents the theoretical analysis of QCL’s beam divergence. The electromagnetic field in the
resonator is calculated according to effective index method. Theoretical results are compared with measurements.
The paper presents results of experimental investigations of spatial distribution of radiation emitted by quantum
cascade lasers. Measurements have been performed by means of a unique goniometric profilometer specially de-
signed for the large angle laser beams. The advantages and limitations of the set-up and the applied experimental
method are discussed. The obtained results have enabled the analysis of dependence of geometry of the beam
on the geometry of the laser structure and on the mount method of the laser chips. The angular divergence of
the beams has also been tested as a function of laser power supply.
We report on detailed investigation of thermal performance of AlGaAs/GaAs quantum cascade lasers (QCL) emitting at
wavelength of 9.4 ìm, with a particular emphasis on the influence of different mounting options and device geometries,
which are compared in terms of their influence on the relative increase of the active region temperature. The spatially
resolved thermoreflectance (TR) is used to register temperature distribution over the facet of pulse operated QCLs. The
devices' thermal resistances are derived from experimental data. Thermal resistances of 15 ìm devices are the highest
among the investigated device widths. By combining the experimental and numerical results, an insight into the thermal
management in QCLs is gained. The thermal design focuses on optimization of heat dissipation in the device, improving
the thermal behavior of QCLs. This is essential in order to increase the maximal operation temperature to further
progress the applications of QCLs.
We report on the study of the temperature influence on optical and electrical performance of the mid-IR GaAs/AlGaAs
QCLs. The temperature dependence of the threshold current, output power, slope efficiency, wall-plug efficiency,
characteristic temperatures T0 and T1, and waveguide losses is investigated. In addition, the influence of different mesa
dimensions on the QCL parameters is analyzed. Experimental results clearly indicate that among the examined
geometries the 25μm wide mesa devices exhibit the best operational parameters i.e., the highest Tmax and T0, highest
wall-plug and slope efficiency, as well as a small temperature increases and the smallest thermal resistivity in the active
area. The knowledge of the above parameters is crucial for designing GaAs/AlGaAs-based devices for high temperature
operation.¬«
In this paper we present the development of mid-infrared GaAs/AlGaAs QCLs technology and discuss basic
characteristics of lasers fabricated at the Institute of Electron Technology. We also show that reliable simulation methods
which can deal with the complicated physical phenomena involved in the quantum cascade lasers operation are necessary
to predict the behaviour of new structures and optimize their performance. The developed lasers show the record pulse
powers of 6 W at 77 K and up to 50 mW at 300 K. This has been achieved by careful optimization of the epitaxial
process and by applying a high reflectivity metallic coating to the back facet of the laser. The devices have been
successfully used in prototype ammonia detection system working in ppb range.
Design and fabrication of saturable Bragg reflectors (SBRs) by molecular beam epitaxy (MBE) is presented. Grown
structures consisted of AlAs/GaAs quarter-wave layers with low-temperature InGaAs/GaAs quantum wells (LT QWs) as
saturable absorber layers. Special emphasis is put on methodology of wavelength tailoring of distributed Bragg reflectors
and on MBE technology of growing the quantum wells with the recombination time of excitons of the order of tens ps.
Application of different methods of characterization of LT QWs and SBRs for testing and optimizing the MBE process is
discussed.
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