This paper deals with thermal annealing time effects on thermal conductivity and optical properties of GaInAsSb grown on GaSb substrate. An increased thermal conductivity as high as 13 W/mK for GaInAsSb layers annealed during 60 min could be measured by photothermal deflection spectroscopy technique (PDS). In addition, a blue shift around 30 meV for as grown GaInAsSb layer compared to the annealed one for 60 min could be put in evidence. From an other hand, the amplitudes signal of PDS reveal a multiple reflection as function of wavelength which appear for all annealed GaInAsSb. Such multiple reflections reflect both a high crystalline quality of the layer and sharp interfaces as well as a good lattice matching between the layer and the substrate. A slight decrease in absorption coefficient is however related to the increase of the reflection coefficient with annealing time.

Photothermal deflection technique (PTD) is used to investigate the effects of thermal annealing time on non-radiative recombination parameters i.e. nonradiative lifetime of minority carriers, electronic diffusion coefficient, and surface and interface recombination velocity of AlGaAsSb/GaSb laser structure. The extraction of the electronic parameters are performed by PTD technique through extensive modeling by fitting the experimental photothermal signal to the corresponding theoretical ones. We have found that nonradiative recombination parameters have been enhanced by annealing time. These results are very promising for improvement of active layer used for vertical-cavity surface-emitting lasers (VCSELs).

In this paper, we have investigated the effects of thermal annealing on optical properties and thermal conductivity of AlGaAsSb/GaSb laser structure using photo-thermal deflection spectroscopy PDS. In fact, optical absorption spectrum and thermal conductivity have been determined by comparison between experimental and theoretical phase of PDS signal. We have found that band gap energy is blue shifted of 70 meV for the as grown to the sample annealed for 1 h. Indeed, the highest thermal conductivity is found around of 11 W/m.K for AlGaAsSb/GaSb annealed for 1 h, which presents a promising result for vertical-cavity surface-emitting lasers (VCSELs). (C) 2017 Elsevier B.V. All rights reserved.

The recognition of aquatic organisms plays a crucial role in the monitoring of the pollution and for the adoption of rapid preventive actions. A compact microscopic optical imaging system is proposed in order to acquire and treat the multibands fluorescence of several pigments in phytoplankton organisms. Two algorithms for automatic recognition of phytoplankton were proposed with a minimum number of calibration parameters. The first algorithm provides a morphological recognition based on "watershed" segmentation and Fourier descriptors, while the second one builds fluorescence pigment images by "k-means" partition of intensity ratios. The operation of these algorithms was illustrated by the study of two different organisms: a cyanobacteria (Dolichospermum sp.) and an alga (Cladophora sp.). The family and the genus of these organisms were then classified into a database which is independent of the size, the orientation and the position of the specimens in the images.

Layers of Ga2O3 alloyed up to 15 at% with Sn4+ has been studied after treatment by RF plasma. An increased conductivity was measured which is an interesting step towards transparent contacts for UV-emitting photonics devices.

Ga2O3 thin films, alloyed with SnO2, ranging from 0 to 15 at% of Sn in composition, were grown by hot wire chemical vapor deposition on C-oriented sapphire. No conductivity was measured on the as-grown or annealed at 1000 °C samples while UV transparency was high. This contradicts the literature works on the effect of Sn4+ doping in films obtained by other methods. Besides, X-ray diffraction patterns showed the epitaxial stabilization of a new phase. The films treated by radio-frequency plasma (hydrogen and argon) presented a decrease in transparency and an increase in conductivity. The conductivity also depended on the SnO2 concentration. The hydrogen doping levels as well as polarons (due to oxygen non-stoichiometry) are suspected to play a role on the conductivity mechanism.

10-period Al0.57Ga0.43N/Al0.38Ga0.62N multi-quantum wells (MQWs) were grown on a relaxed Al0.58Ga0.42N buffer on AlN templates on sapphire. The threading dislocations and V-pits were characterized and their origin is discussed. The influence of V-pits on the structural quality of the MQWs and on optical emission at 280nm was analyzed. It was observed that near-surface V-pits were always associated with grain boundaries consisting of edge threading dislocations originating from the AlN/Al2O3 interface. Although the high density of V-pits disrupted MQWs growth, it did not affect the internal quantum efficiency which was measured to be ~1% at room temperature even when V-pit density was increased from 7×107cm−2 to 2×109cm−2. The results help to understand the origin, propagation and influences of the typical defects in AlGaN MQWs grown on AlN/Al2O3 templates which may lead to further improvement of the performance of DUV devices.

Blooming of algae and more generally phytoplankton in water ponds or marine environments can lead to hyper eutrophication and lethal consequences on other organisms. The selective recognition of invading species is investigated by automatic recognition algorithms of optical and fluorescence imaging. On one hand, morphological characteristics of algae of microscopic imaging are treated. The image processing lead to the identification the genus of aquatic organisms and compared to a morphologic data base. On the other hand, fluorescence images allow an automatic recognition based on multispectral data that identify locally the ratio of different photosynthetic pigments and gives a unique finger print of algae. It is shown that the combination of both methods are useful in the recognition of aquatic organisms.

In this work, wurtzite BAlN layers with boron composition as high as 12% were successfully grown by MOVPE. The growth was performed at 650 °C and then annealed at 1020 °C. Low temperature growth was used in order to alleviate B‐rich phase poisoning under high TEB/III ratio. The growth was performed by continuous epitaxy as well as by flow‐modulate epitaxy. BAlN single layers with clearly defined X‐ray diffraction peaks were achieved on AlN templates which are appropriate substrates for deep UV devices, as well as on GaN templates to facilitate distinguishing of the XRD peak of BAlN from the substrate peak. The layer demonstrated columnar crystalline features and inherited wurtzite structure from substrates.Cross‐section STEM image (bright field) of 75 nm thick BAlN layers containing 12% boron taken along the [11−2 0] zone axis. Zone A is lattice‐oriented along c‐axis and zone B has columnar structure; (b) higher magnification image for the top part of the layer; (c) higher magnification image for the film/substrate interface.

This work is devoted to the design of high contrast grating mirrors taking into account the technological constraints and tolerance of fabrication. First, a global optimization algorithm has been combined to a numerical analysis of grating structures (RCWA) to automatically design HCG mirrors. Then, the tolerances of the grating dimensions have been precisely studied to develop a robust optimization algorithm with which high contrast gratings, exhibiting not only a high efficiency but also large tolerance values, could be designed. Finally, several structures integrating previously designed HCGs has been simulated to validate and illustrate the interest of such gratings.

Nitrogen dioxide is a well-known pollutant which has effect on human health, with pulmonary problems, and on the atmosphere chemistry, where it is responsible for acid rains for example. Consequently, current European standards impose very low NO 2 emission thresholds in exhaust gases. Thus, there is a need for novel sensors able to monitor small NO 2 concentrations for real time adjustments of engines performances. In this perspective, absorption spectroscopy is a method of great interest as it has been largely used in the past to measure NO 2 concentration in air atmosphere. Such measurements require the knowledge of the NO 2 absorption cross-sections. As the atmosphere is a "cold" environment, these data is only known up to 25°C. The first purpose of this study is then, to measure the absorption cross-sections of NO 2 at higher temperatures, i.e. up to 150°C. Then, based on these results, absorption measurements were performed on hot gas mixtures containing very small concentrations of NO 2 (<;5ppm). A resolution close to one part per million was observed.

Five-period AlN/BAlN heterostructure containing boron as high as 11% has been successfully grown by MOVPE. Good periodicity of two alternative layers has been observed by both SIMS profile and Z-contrast HAADF-STEM images. The BAlN layers demonstrate columnar polycrystalline feature. The BAlN layers exhibit an emission peak by CL and absorption edge in transmission spectra at around 260 nm. The results enable the development of BAlGaN based multi-layered heterostructure for UV and deep UV applications.

We report on the growth of Al0.57Ga0.43N/Al0.38Ga0.63N MQWs grown on a relaxed Al0.58Ga0.42N buffer on AlN template by Metal Organic Vapor Phase Epitaxy. The MQW structure is designed so that the strain in the quantum wells induced by their lattice mismatch with barriers is sufficient to enhance TE polarized emission (E-field perpendicular to c). A 630-nm thick relaxed Al0.58Ga0.42N buffer grown on AlN template serves as a pseudo-substrate to release the strain in the barriers and to avoid related defects or composition fluctuation in the active region. Thin (< 2 nm) quantum wells allow preservation of the overlapping of electron and hole wavefunctions considering the strong quantum-confined Stark effect in AlGaN-based MQW structures. Scanning transmission electron microscopy (STEM) coupled to energy-dispersive X-ray spectroscopy (EDX) analysis is used to optimize the growth conditions and to determine the composition of wells and barriers. Optical characterizations of the grown structure reveal a well-defined band-edge emission peak at 285 nm. Based on macro-transmission measurements and simulations, the absorption coefficient of the wells is estimated to be 3 x 10(5) cm(-1) (E-field perpendicular to c), attesting that the oscillator strength is preserved for these AlGaN MQWs with high Al content, which is promising for efficient surface-emitting devices in the deep ultra-violet (DUV) region. (C) 2015 Optical Society of America

In this paper, the effects of zinc proportion in structural, electrical, and optical properties of In2O3 thin films were investigated. 100 nm-thick crystallize indium-zinc-oxide (IZO) thin films were grown by spray pyrolysis method on C-plan sapphire, (001)-silicon, (001)-GaN template and YSZ substrates. The electrical conductivity measurements show a strong influence of the substrates. The best composition for 3 mu m Vertical Cavity Surface Emitting Laser (VCSEL) top contact is found at 30% at. Zn with a maximum IR transparency of 80%. The possibility to synthetize a p-type thin films was also demonstrated.

The identification of phytoplankton is currently an important issue to prevent the aquatic environment. The growth of one or several phytoplankton species can lead to hyper eutrophication and causes lethal consequences on other organisms. In this paper, the selective recognition of invading species is investigated by automatic recognition algorithms of optical and fluorescence imaging. Firstly, morphological characteristics of algae of microscopic imaging are treated. The image processing lead to the identification the genus of aquatic organisms and compared to a morphologic data base. Secondly, fluorescence images allow an automatic recognition based on multispectral data that identify locally the ratio of different photosynthetic pigments and gives a unique finger print of algae. It is shown that the combination of both methods are useful in the recognition of aquatic organisms.

Sn-doped ZnO thin films with 0%, 0.5%, 1%, 1.5% and 2% Sn were grown by spray pyrolysis method on glass substrates under optimized conditions. High resolution Field Effect Scanning Electron Microscopy characterization showed that the films consist of hexagonal-like grains. A comprehensive study of the optical properties was performed and the dispersion constants were determined. The effect of Sn content on the optical band gap and the optical constants (refractive index, extinction coefficient, dielectric constants, and dispersion parameters) was studied. These Sn-doped ZnO thin films are highly transparent (73-93%) in the visible region. A blue shift of the optical band gap, attributed to the Burstein Moss effect, was observed for the Sn-doped films. All the optical dispersion parameters depend on the Sn content of the films, but were found to reach threshold values at a Sn content of 0.5%. These optical parameters are discussed in terms of the single oscillator model. This study demonstrated that this 0.5% Sn-doped ZnO thin film has enhanced physical properties, allowing its better integration in optoelectronic devices. (C) 2014 Elsevier B.V. All rights reserved.

Boron containing III-nitrides are attractive system for deep-UV LEDs and LDs because of their wide bandgaps and flexible lattice. However the crystallinity and boron content have been limited due to large mismatch between BN and other nitrides. In this work, BAlN layers with boron composition from 1% to 5% were successfully grown on AlN template substrates by low-pressure organometallic vapor phase epitaxy. The samples were grown at 650˚C and then annealed at 1020˚C for recrystallization. Growth techniques such as temperature, growth time and TEB/III ratio in the gas phase were investigated. High quality BAlN layers were grown using flow-modulate epitaxy method that allows to enhance surface migration of boron atoms. 70 nm-thick layers show a good surface morphology. For the first time, clear XRD peak relating to 5% boron for this new material was observed, which suggests the formation of single-phase solid solution. Adding more boron to the AlN produced a shift in the peak positions to greater angles. Further results by TEM and optical characterizations will be presented. This new material is promising for deep-UV applications and gives more freedom for bandgap engineering of multi-structure devices.

Photoluminescence of (0001) epitaxial ZnO films with thicknesses of 10, 30 and 100 nm on C-sapphire substrates have been studied at room temperature and after exposure to Ar, Ar-O-2, Ar-N-2 and Ar-H by remote microwave and radiofrequency plasmas. The photoluminescence are not modified by remote plasma treatments where only neutral species were involved. On the contrary, the photoluminescence signal is enhanced or quenched after radiofrequency plasma treatments when energetic ion species are involved in the surface treatment processes. Little changes of electric properties are observed, however, the optical transmission indicates that the absorption edge and probably also the index of refraction are affected. Photoluminescence peak shifts, widths and intensities changes show very strong similarities with polarized emission of ZnO single crystal where it exists a strong dichroism. The photoluminescence emission properties may then result from this optical modification. However, the plasma treatments on the different samples show very low stability in time, except, for the treatment in argon plasma alone. In this later case, in-situ monitoring of photoluminescence as a function of temperature revealed a partial recovery of the photoluminescence properties after a heat treatment at 400 degrees C for few minutes. These results indicate that photoluminescence of (0001) ZnO thin film, related to sigma-emission polarized emission from c-axis polar surfaces, is highly affected by surface and implanted charged species. (C) 2014 Elsevier B.V. All rights reserved.