A number of methods have been demonstrated to increase the sensitivity of fiber refractometers to changes in the surrounding media refractive index (SMRI). The sensor system is based on the effect of lossy mode resonance (LMR) in a thin multimode fiber with a thin film coating. A chemically resistant thin film of aluminum oxide (Al2O3) was applied to the silica surface of an optical fiber by metalorganic chemical vapor deposition (MOCVD). For the first time, the possibility of obtaining aluminum oxide from a vapor-gas mixture of trimethylaluminium - isopropyl alcohol in a hydrogen reducing medium to reduce the carbon content in the sediment has been demonstrated. Using in situ control during the deposition of the coating, the movement of resonances in the transmission spectrum of the optical path was observed. The optical parameters of the deposited coating under various synthesis conditions in the temperature range from 470 to 550 degrees C were estimated by the movement, shape and depth of several orders of resonances. When creating test sensors, deposition was stopped when the resonance was in the spectral range of 400-1700 nm and their sensitivity in aqueous salt solutions (NaCl), as well as chemical resistance in acids (HCl, HNO3, H2SO4, H3PO4) were evaluated. The maximum sensitivity of the implemented sensors for media with refractive indices of 1.34-1.37 was 2950 nm/RIU, which is one of the highest values found in the literature for sensors with Al(2)O(3 )coating. The dependence between the temperature of the synthesis of coatings and the rate of their dissolution in orthophosphoric acid is demonstrated. It is shown that an increase in sensitivity of up to 30 % can be realized by changing the roughness of the surface of the coating or silica glass.

A technique for obtaining vanadium oxides of various stoichiometries from vanadyl isopropoxide by chemical vapor deposition is demonstrated. Various vanadium oxides from the Magnelli series have been obtained. Thin-film coatings are applied to the surface of silicon and sapphire. Coatings deposited in an argon flow at temperatures from 220 ˚C to 290 ˚C were evaluated by transmission spectra, Raman scattering and X-ray diffraction. Four oxides (V3O5, VO2, V6O13, V2O5) with different ratios were found in the synthesized amorphous structures. In a number of coatings on silicon substrates, a phase transition of the second kind with a jump in electrical resistance up to 10 times at a temperature of 69 ˚C, was recorded.

Short tapered fiber sections 3-10 mm in length and 12-20 microns in diameter were fabricated through the partial etch removal of the outer silica cladding. ZnTe and Bi2Te3 crystalline films 1-60 nm thick were subsequently applied to the surface of the tapered fiber sections using metalorganic chemical vapor deposition. Transmission spectra of the taper were recorded within the wavelength region of 1-1.6 mu m at regular intervals whilst the deposition. Strong decreases in transmission in relatively narrow spectral bands were observed. The results can be applied to lossy mode resonance fiber sensors and passively mode-locked pulsed fiber laser designs.

Metal organic chemical vapour deposition (MOCVD) technology is adapted for the deposition of thin zinc and bismuth chalcogenides films on the surface of silica optical fibres with short tapered sections. Growth runs were carried out in a special tubular quartz reactor at atmospheric pressure of hydrogen at 425°C temperature using ZnEt2, BiMe3, Et2Te and i-Pro2Se as organometallic precursors. During the deposition of chalcogenides, the transmittance spectra of the fibre were recorded in regular short time intervals. In the transmittance spectra of the fibre with a tapered section coated by ZnSe and ZnTe, lossy mode resonances (LMR) were observed at a diameter of the tapered waist below 30 μm. After the deposition of very thin Bi2Te3 and Bi2Se3 island films on the tapered waist with a diameter about 10 μm optical fibres were built into erbium fibre ring lasers. A pulsed generation mode was achieved in some of lasers due to resonator Q-factor modulation. These results can be applied for the design of LMR fibre sensors and passively Q-switch pulsed fibre lasers.

Performance of a passively Q-switched erbium fiber laser with a narrow bandgap Bi2Te3 semiconductor thin film used as a saturable absorber was studied experimentally. In order to obtain repetitively-pulsed lasing, a Q-switcher was fabricated as a section of the standard SMF-28 optical fiber with a short (∼4 mm in length) chemically etched out tapered section laterally covered with the bismuth telluride film. This Q-switcher was installed in a specially designed circuit of a ring-type erbium fiber laser pumped by a laser diode at 975 nm wavelength. The fiber diameter in the middle of the tapered section was 10-15 μm. Two types of taper coverage were studied: Bi2Te3 flakes suspended in isopropanol and a ZnTe/Bi2Te3 uniform polycrystalline thin-film heterostructure synthesized on a lateral surface of a tapered fiber section via MOCVD. In the first case, we observed laser oscillation at a wavelength of 1565 nm as a train of 7-26 μs pulses with a 86-50 μs repetition period at pump powers varying from 26 to 75 mW. In the second case, CW oscillation in the circuit appeared at a pump power of 30 mW while conversion to the repetitively-pulsed mode with a kilohertz repetition rate occurred at pump powers within the range of 34-40 mW. The results obtained indicate the feasibility of effective interaction of the evanescent field with a bismuth telluride film used as a saturable absorber. This interaction is sufficient to achieve a stable repetitively-pulsed lasing in the circuits of passively Q-switched fiber lasers.

Crystalline 2D bismuth and antimony chalcogenides, as well as graphene, can successively operate as saturable absorbers in various schemes of passively mode-locked fibre lasers. An attractive benefit of these saturable absorbers is their power to effectively operate at different wavelengths in the wideband from 1 to 2 microns. However, the problem is how to provide a reliable interaction between light in a fibre and the absorber. The main disadvantage of a standard solution to the problem essentially is to use exfoliated flakes dissolved in a coupling agent, which deposits additional heat that negatively affects the absorber. In the present research, thin crystalline films of a narrow-band semiconductor Bi2Te3 were deposited directly on silica optical fibres by means of metal-organic chemical vapour deposition (MOCVD). A ZnTe buffer layer was deposited first in a single growth run, providing the necessary condition for better adhesion of bismuth telluride film to the silica surface. Two types of fibre coatings were prepared and tested: the coating upon the cleaved end of the fibre and the one upon the lateral surface of the light-guiding fibre core. In the latter case, prior to deposition a fibre section of about 1 cm in length was uniformly thinned via chemical etching to a diameter of about 20 microns. Reflection and transmission of the growing films were monitored in situ during the deposition.

We present a first study of films of the quaternary Bi2-xSbxTe3-ySey solid solutions on (0001) sapphire substrates grown by atmospheric pressure MOVPE. Trimethylbismuth, trimethylantimony, diisopropy-lselenide and diethyltelluride were used as precursors. To passivate the free bonds of the substrate and to improve the epitaxy, a thin (15 nm) ZnTe buffer layer was first grown. EDX analysis of the films grown at a temperature of 445 degrees C and about 10-fold excess of chalcogen in the vapor phase indicates on their compliance with V2VI3 stoichiometry. AFM and SEM investigations showed that at the initial stage of deposition the Stranski-Krastanov growth mode is dominant. Complete coalescence of nanoislands occurs at a thickness about 60 nm and further film formation is in the 2D layer-by-layer growth mode. A high mole fraction of antimony in the vapor phase leads to bad crystalline quality of the films and even to their discontinuity. Transport properties of the Bi2-xSbxTe3-ySey films were evaluated using Van der Pauw Hall effect measurements in the range of temperatures of 10-300 K. Some films are always n- or p-type; in other samples the change of conductivity from p-to n-type was observed when the temperature decreases. (C) 2017 Elsevier B.V. All rights reserved.

The films of Sb-Te system have been deposited by MOVPE on (0001) Al2O3 substrates with thin ZnTe buffer layers at different temperatures and Te/Sb ratios in the vapor phase. X-ray diffractometry, SEM microscopy, Raman and EDX spectroscopy were used to study as-grown films. The surface morphology and stoichiometry of Sb-Te films strongly depend on Te/Sb ratio in vapor phase. We have deposited the phases of homologous series nSb2·mSb2Te3 with following stoichiometries: Sb2Te3, Sb4Te5, Sb8Te9, Sb10Te9, Sb4Te3, Sb2Te, Sb8Te3, Sb10Te3, Sb16Te3, Sb18Te3 and Sb. Transport properties of Sb2Te3, Sb4Te5, Sb8Te9, Sb4Te3, Sb2Te were evaluated using Van der Pauw technique at 300K.

We studied the metalorganic vapor phase epitaxy (MOVPE) of (B1-xSbx)(2)Se-3 solid solution films with a different Sb content on (001) Al2O3 substrates with thin ZnSe buffer layer in the range of temperatures 250-480 degrees C. As-grown films were studied by atom force and scanning electron microscopy (AFM and SEM), Raman spectroscopy and X-ray diffractometry (XRD) techniques. To determine the elemental composition of the grown films, we used an energy dispersive spectrometer (EDS). The dependencies of the crystal structure of films on the growth temperature and Sb content (0 <= x <= 1) were explored. At different growth temperatures we obtained the following bismuth compounds: the films grown at the temperature of 370 degrees C or lower consist of the pure Bi phase, whereas we got the Bi4Se3 phase at 380 degrees C, the phase BiSe at 430 degrees C and Bi2Se3 at the temperature of 460 degrees C or above. We found out that at the temperature of 480 degrees C the single-phase films of (B1-xSbx)(2)Se-3 with rhombohedral and orthorhombic lattices are realized when x is less than 0.25 and greater than 0.935, respectively. For 0.25 < x < 0.935 the grown films are composites of rhombohedral and orthorhombic phases. At the temperature of 440 degrees C we obtained films consisting of three rhombohedral phases (B1-xSbx)(4)Se-3, (Bi1-xSbx) Se and Bi. The room temperature transport properties of rhombohedral samples were characterized using the Van der Pauw technique. (C) 2015 Elsevier B.V. All rights reserved.

We have deposited films of Bi-Te system by atmospheric pressure MOVPE on (0001) Al2O3 substrates with thin ZnTe or thick GaN buffer layers at different temperatures and Te/Bi ratio in the vapor phase. As-grown films were studied by X-ray diffractometry, SEM microscopy and Raman spectroscopy. To determine the elemental composition of the films, an energy dispersive spectrometer was used. Single-phase films of Bi2Te3, Bi4Te5, BiTe, Bi10Te9, Bi4Te3, Bi3Te2 have been grown and growth parameter ranges for obtaining different phases were defined. It was found that under the same growth condition different phases of the Bi-Te system realize depending on the film's thickness. Thus, when growing of Bi2Te3 films by MOCVD method the careful control of the phase composition is required.

We report on a metal organic vapor epitaxy (MOVPE) of Bi2Te3−xSex films over the entire range of compositions (0≤x≤3) for the first time. The films were grown on Al2O3(0001) substrates at 465°C using trimethylbismuth (Bi2Me3), diethyltellurium (Et2Te) and diisopropylselenium (iPro2Se) as metalorganic sources. To realize the 2D growth mode and to grow films with flat surfaces and high crystalline quality, a thin ZnTe buffer layer was used. As-grown films were studied using optical and AFM microscopy techniques and X-ray diffraction. It was found that under steady growth conditions the composition of Bi2Te3−xSex films strongly depends on the film thickness. But a high rate of interdiffusion of chalcogens at the growth temperature rapidly leads to a homogeneous composition of the film in the growth direction. Dependence of the intensity of X-ray reflection (0012) on the composition of Bi2Te3−xSex films x has extremes near x=1 (Bi2Te2Se) and x=2 (Bi2Se2Te). The AFM micrographs and profiles show large (above 2μm) triangle-shaped atomically flat terraces with step height of a quintuple layer (0.90nm) of the tetradymite-type compounds. The electronic properties of the grown films have been characterized via four probe magnetotransport measurements.

Due to large exciton binding energy, ZnO/ZnMgO heterostructures are promising for modern optoelectronic devices in the UV range. We report on the metal-organic vapor phase epitaxy (MOVPE) of ZnO, ZnMgO layers and periodic ZnO/ZnMgO MQW structures at atmospheric hydrogen pressure using diethylzinc (DEZ), bismethyl-cyclopentadienil-magnesium ((MeCp)2Mg) and tertiary-butanol (t-BuOH) as precursors. Wurtzite-type layers and MQW structures were grown below 450°C on Al2O3(0001) substrates. The growth rate is constant in the temperature interval from 170 to 430°, and decreases abruptly above 430° as a result of ZnO decomposition in hydrogen. PL and X-ray measurements confirm a wurtzite structure f ZnMgO films with a Mg content of up to 35 at%. The as-grown films show good optical quality and near band edge emission in the photoluminescence (PL) and cathodoluminescence (CL). Periodic ZnO/ZnMgO MQW structures with strong ZnO QWs emission were grown at room temperature.

ZnCdSe/ZnSSe MQW structures for an electron beam pumped VCSEL with resonant periodic gain were grown by MOVPE at 425-470 degrees C. Strong contamination of the structure by Ga from a GaAs substrate was found and its effect on the growth rate and photoluminescence characteristics was studied. A protective thin ZnSSe layer deposited at lower temperature (350 degrees C) or thin layers of ZnS and ZnS/ZnSSe SL grown at temperature 425-470 degrees C prevent Ga penetration and allowed improving the quality and periodicity of the structure. Based on the grown MQW structure, green VCSEL was fabricated. Lasing at 542 nm with 3 W output power was achieved at RT and 40 keV. The threshold was as low as 8 A/cm(2). (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nonlinear optical response of periodic structures based on ZnSe/ZnS heterostructures using interband excitation of a ZnSe sublattice by 150 fs laser pulses is reported. A considerable shift of reflection spectrum and large relative reflection changes were observed in a wide spectral range corresponding to the transparency region of ZnSe far from the intrinsic absorption onset. Evaluated refraction index change is about -0.02 with the relaxation time being about 3 picoseconds. The nonlinear refraction is supposed to be controlled by population induced absorption changes in Znse single crystals and relevant refraction index modification via Kramers-Kronig relations. The nonlinearity relaxation time is supposed to trace a transition from non-equilibrium to quasi-equilibrium distribution of electrons and holes within ZnSe conduction and valence bands, respectively, rather than electron-hole recombination time. The nonlinearity mechanism does not reduce to just population dependent absorption saturation but essentially results from the specific distribution function in the first instance after excitation.

30-55 period ZnSSe/ZnMgSSe MQW structures were grown by metal-organic vapour phase epitaxy on GaAs substrates. Band gap of ZnMgSSe barriers was about 3 eV at room temperature. Based on these structures an etalon for vertical cavity surface emitting laser with resonant periodic gain was fabricated. Single mode lasing at lambda =462 nm with 0.6 W output power was achieved under scanning electron beam pumping at room temperature. Irregular spectral position of cavity modes is discussed. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

This report summarises recent progress towards the realisation of Laser Cathode Ray Tube (LCRT) devices on the basis of II-VI semiconductors. Although such devices were demonstrated over 30 years ago, using bulk crystalline materials as the active media, practical lasers that operate at room temperature for extended periods of time are not yet readily available. We aim to overcome this roadblock by reducing the threshold power densities of working lasers. By embedding heterostructures, grown using metalorganic vapour phase epitaxy (MOVPE), within all-dielectric microcavities, the necessary threshold reductions can be made. The construction and testing of an exemplar device, based upon CdSSe/CdS (hex) multiple quantum wells, is described.

Mirror-like hexagonal CdS, ZnCdS layers and CdS/ZnCdS quantum well (QW) structures have been grown on CdS(0001) and ZnCdS(0001) substrates by metalorganic vapour-phase epitaxy. CdS and ZnCdS epilayers with high cathodoluminescence (CL) intensity at room temperature have been obtained by optimization of growth conditions. Two additional emission lines, not observed in CdS bulk crystals, appear in low temperature CL spectra. These lines can be ascribed to thin cubic layers due to stacking faults at growth of the hexagonal CdS epilayer. CL spectra of CdS/ZnCdS QW structures contain intense CdS QWs emission lines. With increasing excitation intensity the short-wavelength shift of the QW emission line is a manifestation of internal piezoelectric effect.

Optimization of growth conditions allows us to grow mirror-like hexagonal ZnCdS layers and CdSSe/ZnCdS quantum well (QW) structures on CdS(0001) and ZnCdS(0001) substrates by MOVPE. ZnCdS epilayers with high cathodoluminescence (CL) intensity at room temperature (RT) have also been obtained. An intense QW emission line has been observed in CdS/ZnCdS QW structures. With increasing excitation intensity the line shifted to shorter wavelength, which is a manifestation of an internal piezoelectric effect. An additional short-wavelength line appears in low-temperature CL spectra of CdSSe/ZnCdS QW structures due to localization of charge carriers by nonuniformity of alloy composition or QW thickness.