LEDs based on InAsSbP/InAsSb heterostructures (λ = 4.7 μm) for carbon monoxide detection

Light-emitting diodes (LEDs) operating in the 4.4–4.8-μm wavelength range have been developed for detecting the presence of carbon monoxide (CO) in air. The proposed LEDs are based on InAsSbP/InAsSb heterostructures with InAs_0.85Sb_0.15 active region, which were grown by metalorganic vapor-phase epitaxy. The electrolumuinescent properties of LEDs have been studied. The output power of LED operating in a pulsed mode reaches 50 μW at a current pulse amplitude of 2 A, and that in a quasi-continuous wave mode is 1 μW at a current of 200 mA. The absorption of LED radiation in a gaseous medium containing 10% CO has been studied. The proposed LEDs can be used to simultaneously detect both CO₂ (absorbing at λ = 4.3 μm) and CO (λ = 4.67 μm).     

LEDs based on InAs/InAsSb heterostructures for CO<Subscript>2</Subscript> spectroscopy (λ = 4.3 μm)

Light-emitting diodes (LEDs) operating in a 4.1–4.3 μm wavelength range have been created on the basis of InAs/InAsSb heterostructures grown by metalorganic vapor-phase epitaxy. The output radiation power of LEDs is increased using flip-chip design. Investigation of the electrolumuinescent properties of LEDs with smooth and profiled output edge surface showed that the latter LEDs possess a greater efficiency, which is related to an increase in the radiation yield due to multiply repeated reflection from the curved surface. The output power of LED operating in a quasi-continuous wave mode was 30 μW at a current of 200 mA and that in a pulse mode was 0.6 mW at a current pulse amplitude of 2 A.     

Increasing output power of LEDs (λ = 1.7–2.4 μm) by changing directions of reflected light fluxes in GaSb/GaInAsSb/GaAlAsSb heterostructures

It is demonstrated, using the example of light-emitting diodes (LEDs) based n-GaSb/n-GaIn-AsSb/p-GaAlAsSb heterostructures, that the formation of a curvilinear reflecting surface consisting of hemispherical etch pits on the rear side of an LED chip leads to an increase in the output radiation power by a factor of 1.9–2 in the entire wavelength interval studied (λ = 1.7–2.4 μm) as compared to the LED chip design with a continuous absorbing ohmic contact. This increase in the LED efficiency is related to a change in the directions of reflected light fluxes upon reflection from the hemispherical etch pits.     

AlGaAs/GaAs multiquantum-well heterostructures for long-wavelength (8–10 μm) IR photodetectors

We have studied AlGaAs/GaAs multiquantum-well heterostructures grown by molecular beam epitaxy in an STE-3532 setup (SemiTEq, St. Petersburg), which are intended for long-wavelength IR photodetectors operating on inter-subband transitions. Quantum wells (QWs) in the obtained heterostructures are highly homogeneous and possess sharp heteroboundaries, which is confirmed by the photoluminescence spectra and dark current-voltage characteristics of photodetectors based on these heterostructures. The photodetectors exhibit sensitivity in the atmospheric transparency window (8?C10 mm) and possess parameters that make possible their use in large-format photodetector arrays for a new generation of long-wavelength IR camera systems.     

Frequency-tuned semiconductor whispering-gallery-mode laser (λ = 2.35 µm) operating at room temperature

Technical Physics Letters - Frequency tuning in a whispering gallery mode (WGM) semiconductor laser (λ = 2.35 µm) with a sector (half-disk) cavity has been studied. Pumping by current...     

Uncooled photodiodes based on InAsSb(P) with long-wavelength cut-off at λ = 5.8 μm

We have experimentally studied the parameters of room-temperature photodiodes based on gradient solid solutions of the InAsSb(P) system, having a long-wavelength cut-off at λ = 5.8 μm and various geometries of non-transparent contacts on the exposed p-InAsSb(P) surface. It is established that the sensitivity (photocurrent collection efficiency) strongly depends on the perimeter of this contact: photodiodes with net structure of this contact (increased perimeter and area) are characterized by increased sensitivity even despite greater degree of shadowing of the exposed surface by the contact.     

Creating disk-shaped cavity with a vertical side surface for an infrared whispering-gallery-mode laser (λ ≈ 3 μm)

Disk-shaped cavities in the form of cylinders with diameters of 200, 100, and 50 μm and a mesa height of up to 30 m with the vertical part of the side surface reaching 10 m have been created for the first time for whispering gallery mode (WGM) semiconductor lasers based on InAs/InAsSb_0.11P_0.24 heterostructures. The cavities were formed by etching in a specially selected HBr-H₂Cr₂O₇-H₃PO₄ mixture, which ensured an increase in the length of the vertical part of the side surface at a decrease in the surface roughness. These improvements increased the stability of optical modes in the disk cavity of the WGM laser and ensured generation with a wavelength of λ ≈ 3 μm in a continuous regime at 77 K.     

Room-temperature photodiodes based on InAs/InAs<Subscript>0.88</Subscript>Sb<Subscript>0.12</Subscript>/InAsSbP heterostructures for extended (1.5–4.8 μm) spectral range

Photodiodes with a photosensitive area of 0.45 × 0.45 mm² operating at room temperature in a wavelength range bounded by 4.9 μm have been created on the basis of InAs/InAs_0.94Sb_0.06/InAsSbP/InAs_0.88Sb_0.12/InAsSbP/InAs heterostructures grown by liquid phase epitaxy. A distinguishing feature of the proposed photodiodes is extended (λ_max = 1.5–4.8 μm) spectral sensitivity range, in which the photodiode is characterized by a monochromatic responsivity of 0.5–0.8 A/W and a dark current density of 1.0–1.5 A/cm² at a reverse bias of 0.2 V. The differential resistance at zero bias reaches up to 20–100 Ω. The detection ability of photodiodes in the region of maximum sensitivity reaches (1–2) × 10⁸ cm Hz^1/2 W⁻¹.     

Photodiodes based on InAs/InAs<Subscript>0.88</Subscript>Sb<Subscript>0.12</Subscript>/InAsSbP heterostructures for 2.5–4.9 μm spectral range

Photodiodes with a photosensitive area diameter of 0.3 mm operating at room temperature in a middle-IR (2.5–4.9 μm) wavelength range have been created based on InAs/InAs_0.94Sb_0.06/InAsSbP/InAs_0.88Sb_0.12/InAsSbP/InAs heterostructures grown by liquid phase epitaxy. Distinguishing features of the proposed photodiodes are a high monochromatic responsivity, which reaches a maximum of 0.6–0.8 A/W at λ_max = 4.0–4.6 μm, and a low dark current density of (1.3–7.5) × 10⁻² A/cm² at a reverse bias of 0.2 V. The differential resistance at zero bias reaches up to 700–800 Ω. The detection ability of photodiodes in the spectral interval of maximum sensitivity reaches (5–8) × 10⁸ cm Hz^1/2 W⁻¹.     

Structural transformations induced in amorphous free-standing 55wt.%Cr-45wt.%Ni thin films with 2.5 μs (10.6 μm) and 400 μs (0.69 μm) single laser pulses

Experimental results for the pulse laser irradiation of free-standing 55wt.%Cr-45wt.%Ni amorphous thin films with thicknesses ranging from 15 to 60 nm are reported. Transmission electron micrographs and electron diffraction patterns are presented in order to reveal the laser-induced structural transformations.     

Variable temperature laser light scattering microscopy studies on high purity 10–100 μm Ag and Ti metal particles

Abstract

Behaviour of 10–100 μm sized Ag and Ti metal particles was studied by employing laser light scattering microscopy while increasing the temperature at different rates. Differential area ω was defined as 2(A_max?A_min)/(A_max+A_min), and its significance as strain variation response is established. The ω versus dT/dt curves of Ag and Ti were exponential in nature, with positive and negative slopes respectively. The role of smallness of the metal particles vis-à-vis defects was considered. Systematic variation of surface activity S_a with rate of heating is noticed. A plausible reasoning is offered to explain the experimental results qualitatively.     

A generation of 2 μm Q-switched thulium-doped fibre laser based on anatase titanium(IV) oxide film saturable absorber

We demonstrate a Q-switched thulium-doped fibre laser operating at approximately 1935 nm wavelength using anatase titanium(IV) oxide (TiO₂) embedded in polyvinyl alcohol as the passive newly saturable absorber (SA). The film has absorption loss of 3.5 dB and modulation depth of 33%. It is sandwiched between two fibre ferrules in a ring laser cavity to produce self-started pulse train with a repetition rate that is tuned from 30.12 to 36.96 kHz as the 1552-nm pump power is increased from 289 to 485 mW. At maximum pump power, the laser produced a Q-switching pulse train with pulse duration, output power, pulse energy and peak power of 1.91 μs, 11 mW, 0.3 μJ and 146 mW, respectively. These results show that the TiO₂ is a new potential SA material for pulsed laser applications.     

Diode-pumped 2 μm vibronic (Tm3+, Yb3+):KLu(WO4)2 laser

We report on laser operation in a (6 at. % Tm, 5 at. % Yb):KLu(WO4)2 codoped crystal. The vibrational frequencies of KLu(WO4)2 are coupled to the electronic transitions of Tm3+ at 1946 nm, creating virtual final laser levels at higher energy than the ground level 3H6 of Tm3+. The longest recorded laser wavelength was 2039 nm, which is longer than permitted by a pure electronic transition in Tm3+ ions in KLu(WO4)2. We show that every laser wavelength can be explained with the electron-phonon coupling effect, where the vibration frequencies were determined through Raman spectroscopy.     

Self-driven solar-blind ultraviolet photodetectors based on p-Zn1−xSbxO/n-Si− (x = 0.03, 0.05) heterojunction diodes

Journal of Materials Science: Materials in Electronics - Ultra-violet photodetectors based on p-ZnO/n-Si? heterojunctions have been fabricated by radio-frequency magnetron sputtering...     

Interpenetrating polymer networks (IPN) based on gelatin/poly(ethylene glycol) dimethacrylate/clay nanocomposites: Structure–properties relationship

The effects of cross-linking sequence (simultaneous or sequential) and incorporation of exfoliated sodium-montmorillonite (Na⁺-MMT) nanoclay on the structure and properties of interpenetrating polymer networks (IPNs) based on gelatin/poly(ethylene glycol)dimethacrylate were studied by means of different complementary techniques. Gelatin and PEGdmA phases were cross-linked via chemical and in-situ UV curing, respectively. 2,2-dimethoxy-2-phenylacetophenone (DMPA) (1.5% w/w) was used as photo-initiator to cross-link PEGdmA. The results showed that the incorporation of small amount of Na⁺-MMT nanoplatelets accelerates the kinetics of chemical cross-linking of gelatin by glutaraldehyde (1.0% w/w). This led to a new hypothesis concerning the tuning structural evolution of the IPNs by the Na⁺-MMT content. In the case of simultaneous IPNs, in which both phases cross-linked at the same time, the accelerated cross-linking of gelatin in the presence of exfoliated sodium-montmorillonite led to increased structural homogeneity, improved mechanical and thermal properties. Incorporation of nanoclay did not show any significant effect on the structure and properties of the IPNs synthesized via sequential method in which gelatin and PEGdma phases were cross-linked separately. For the semi-IPNs, however, Na⁺-MMT induced macroscopic phase separation and resulted in lower mechanical properties. These results might shed light on the mechanisms underlying structure–property relationship in biohybrid IPNs based on gelatin as promising candidates for tissue engineering and drug delivery applications.     

Mechanochromism of polyurethane based on folding–unfolding of cyano-substituted oligo(p-phenylene) vinylene dimer

The incorporation of mechanophores, motifs that transform mechanical stimulus into chemical reaction or optical variation, allows creating materials with stress-responsive properties. The most widely used mechanophore generally features a weak bond, but its cleavage is typical an irreversible process. Here, we showed that this problem can be solved by folding–unfolding of a molecular tweezer. We systematically studied the mechanochromic properties of polyurethanes with cyano-substituted oligo(p-phenylene) vinylene (COP) tweezer (DPU). As a control experiment, a class of polyurethanes containing only a single COP moiety (MPU) was also prepared. The DPU showed prominent mechanochromic properties, due to the intramolecular folding–unfolding of COP tweezer under mechanical stimulus. The process was efficient, reversible and optical detectable. However, due to the disability to form either intramolecular folding or intermolecular aggregation, the MPU sample was mechanical inert.     

Sol–gel based calcium phosphates coatings deposited on binary Ti–Mo alloys modified by laser beam irradiation for biomaterial/clinical applications

Ti-15Mo alloy samples were irradiated by pulsed Yb: YAG laser beam under air and atmospheric pressure. Calcium phosphate coatings were deposited on the irradiated surfaces by the sol–gel method. The sol was prepared from the precursors Ca (NO₃)₂.4H₂ O and H₃ PO₄. The modified surfaces were submitted to heat treatment conditions at 350 and 600?°C. The results showed that the two conditions established have a sufficient energy to promote ablation on the laser beam irradiated surfaces. Likewise, it has been demonstrated the processes of fusion and fast solidification from the laser beam irradiation, under ambient atmosphere, inducing the formation of stoichiometric TiO₂ and non-stoichiometric titanium oxides, including Ti₃O₅, TiO, Ti₃O and Ti₆O with different oxide percentages depending on the fluency used. Besides that, laser modification has allowed a clean and reproducible process, providing no traces of contamination, an important feature for clinical applications. The physico-chemical and morphological properties indicated the formation of a mixture of phases: calcium pyrophosphate, hydroxyapatite and β-TCP for the procedure (PA: calcination temperature), whereas HA (hydroxyapatite) and β-TCP (tricalcium phosphate) were obtained by the procedure (PB: calcination temperature). Therefore, it was possible to obtain a Ti-15Mo alloy surface consisted on calcium phosphate ceramics of biological interest using the procedure (PB). Thus, the laser beam irradiation associated to bioactive coatings of calcium phosphates of biological interest have shown to be promising and economically feasible for use in dental and orthopedic implants.

Open image in new window

     

Sulfur Adsorbed (Θ=1/2) on Gold (111) Substrate

The adsorption of Θ=1/2 monolayer (ML) of S on Au(111) is calculated. The evolution of the positions of adatoms for 800 K, 500 K, 300 K, 150 K, and 1 K is evaluated by using a density functional theory (DFT)-tight binding approach combined with classical molecular dynamics. For this coverage, there is a controversy about the existence of superficial composite AuS or molecular aggregates. We find a configuration in which sulfur atoms form quasi-S₂ superficial molecules with total energy very close to the monoatomic phase, suggesting the coexistence of both configurations at room temperature. We find that the stability of the dimeric phase is due to the increase of the binding energies between sulfurs. In the other phase, the stabilization occurs due to a formation of AuS dimers. At high temperatures (T>300 K) sulfurs have high mobility which allows the migration among different adsorption sites. At low temperatures the mobility decreases and a thermal activation barrier of 25–30 meV can be estimated.     

Critical thermistors based on VnO2n−1 (n=3−6)

New types of critical thermistors are proposed, based on V₃O₅, V₄O₇, V₅O₉, and V₆O₁₁. It is shown that they can be prepared from Magnelli-phase single crystals, which do not decompose during the phase change. Volt-ampere characteristics and switching voltage-temperature curves were obtained.     

Simultaneous measurements of CO2 and CO using a single distributed-feedback (DFB) diode laser near 1.57 μm at elevated temperatures

A sensor using a single distributed-feedback (DFB) diode laser at 1.57 μm for the simultaneous measurement of CO(2) and CO concentration at elevated temperatures is developed. A proper line pair near 6361.250 and 6361.344 cm(-1) is chosen based on absorption strength, separation of the two lines, and isolation from interference of neighboring transitions of the major combustion gases. The concentrations of CO(2) and CO are inferred from their wavelength modulation spectroscopy (WMS) 1?-normalized absorption-based WMS-2? signal peak heights. The CO(2) and CO concentration measurements are within 3.3% and 5% of the expected values over the full temperature range.