Nicolas Fressengeas

University of Lorraine | UdL · Laboratoire Matériaux Optiques, Photonique et Systèmes

In this paper, a two-layer model was used to investigate the electrical properties of InGaN epilayer grown by MOCVD on a semiconducting GaN template substrate. The elaboration process was optimized to obtain high-quality InGaN epilayers with respect to the indium composition. The details of structural and optical properties as well as the surface m...

ZnMgO thin films are elaborated by ultrasonic spray pyrolysis using water‐based solutions only, for an Mg composition as high as 70 mol%. The elaboration conditions are optimized and the structural, optical, and electrical properties of the ZnMgO films are investigated with respect to the Mg concentration using X‐Ray fluorescence, X‐Ray diffraction...

Purpose The purpose of this paper is to investigate the effect of growth temperature on the evolution of indium incorporation and the growth process of InGaN/GaN heterostructures. Design/methodology/approach To examine this effect, the InGaN/GaN heterostructures were grown using Taiyo Nippon Sanso Corporation metal-organic chemical vapor depositio...

In this work, ZnO films are deposited by the ultrasonic spray pyrolysis technique on soda lime glass substrates by following a specific design of experiment. The ZnO films are spray deposited using different elaboration parameters. Optical, morphological, structural and electrical properties of the ZnO films are systematically investigated. Fourier...

Numerical simulations of AZO/Zn 1− x Ge x O/Cu 2 O solar cell are performed in order to model for the first time the impact of the germanium composition of the ZnGeO buffer layer on the photovoltaic conversion efficiency. The physical parameters of the model are chosen with special care to match literature experimental measurements or are interpola...

The synthesis of new efficient low cost solar cells made with earth abundant materials requires on the one hand the development of such materials and, on the other hand, an adequate design of the solar cell that optimizes their use. This latter part is all the more challenging as the materials can be tuned in a variety of ways, adjusting for instan...

The development of new thin films solar cells is highly accelerated by using rigorous optimization approach. A large set of parameters is involved in the solar cell operation: active layer thickness, composition, bandgap, doping, contacts, etc. The study of the solar cell performances with respect to these linked parameters is necessary to better u...

The design and optimization of novel structures is an essential part of the next-generation solar cells development. Indeed, the technological steps involved in the development of high-performance solar cells involve a huge set of interdependent physical and geometrical parameters: layers thicknesses, dopings, compositions, and defect characteristi...

Le nitrure d'indium et de gallium (InGaN) est un matériau semi-conducteur utilisé aujourd'hui pour les lasers et les diodes électroluminescentes. Son potentiel pour les cellules solaires (absorption très élevée, résistance aux hautes températures et aux radiations, largeur de bande interdite modulable) est encore inexploité en raison notamment de l...

Choosing the Indium Gallium Nitride (InGaN) ternary alloy for thin films solar cells might yield high benefits concerning efficiency and reliability, because its bandgap can be tuned through the Indium composition and radiations have little destructive effect on it. It may also reveal challenges because good quality p-doped InGaN layers are difficu...

On the road towards next generation high efficiency solar cells, the ternary Indium Gallium Nitride (InGaN) alloy is a good passenger since it allows to cover the whole solar spectrum through the change in its Indium composition. The choice of the main structure of the InGaN solar cell is however crucial. Obtaining a high efficiency requires to imp...

The Indium Gallium Nitride (InGaN) III-Nitride ternary alloy has the potentiality to allow achieving high efficiency solar cells through the tuning of its band gap by changing the Indium composition. It also counts among its advantages a relatively low effective mass, high carriers' mobility, a high absorption coefficient along with good radiation...

Mid-infrared Vertical cavity surface emitting lasers (MIR-VCSEL) are very attractive compact sources for spectroscopic measurements above 2μm, relevant for molecules sensing in various application domains. A long-standing issue for long wavelength VCSEL is the large structure thickness affecting the laser properties, added for the MIR to the tricky...

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 bee...

This paper focuses on the determination of the bandgap energy bowing parameter of strained and relaxed InxGa1−xN layers. Samples are grown by metal organic vapor phase epitaxy on GaN template substrate for indium compositions in the range of 0<x<0.25. The bangap emission en- ergy is characterized by cathodoluminescence and the indium composition as...

A GaAs/AlOx high contrast grating structure design which exhibits a 99.5% high reflectivity for a 425nm large bandwidth is reported. The high contrast grating (HCG) structure has been designed in order to enhance the properties of mid-infrared VCSEL devices by replacing the top Bragg mirror of the cavity. A robust optimization algorithm has been im...

A new mid-infrared (MIR) Vertical Cavity Surface Emitting Laser (VCSEL) structure is proposed. We have integrated to the VCSEL structure both an oxide aperture for lateral confinement, and a sub-wavelength high-contrast-grating top mirror. Upon the GaSb-based half-VCSEL, we have grown a metamorphic AlGaAs heterostructure to enable thermal oxidation...

A time resolved study of the behavior of a single beam in photorefractive iron doped indium phosphide is provided down to the microsecond range, showing that infrared beam bending does occur on the microsecond time scale for moderate beam intensities. Two distinct time scales are evidenced, the behavior of which are the sign of two different photor...

The InGaN ternary alloy has the potentiality to achieve high efficiency solar cells. Indeed the bandgap of the InGaN alloy covers the whole solar spectrum including the visible region by changing the Indium composition. The InGaN alloy also counts among its advantages a relatively low effective mass of electrons and holes, their high mobilities, hi...

Current voltage (I-V) and capacitance voltage (C-V) measurements have been performed versus temperature on GaN Schottky diodes. The results show an increase of the Schottky barrier height ϕb and a decrease of the ideality factor n both with the increase of the temperature. We show that this behavior originates in the existence of an interface state...

High contrast gratings (HCG) have drained recently highly attractive perspectives for VCSEL devices through the wide potentialities for obtaining unique optical properties with these integrable optical elements [1], in contrast to conventional Bragg reflectors. Since most of the HCG approaches on III-V based photonic devices are based on semiconduc...

A Si/Si3N4 high contrast grating mirror has been designed for a VCSEL integration in mid-infrared ({\lambda} = 2.65 $\mu$m). The use of an optimization algorithm which maximizes a VCSEL mirror quality factor allowed the adjustment of the grating parameters while keeping large and shallow grating pattern. The robustness with respect to fabrication e...

This paper presents a way to achieve optical limiting using the self-focusing of a laser beam in a photorefractive medium. In this view, the protection is not based on the absorption of the beam energy in the limiting system but on a global defocusing of the light in the optical system. We have studied experimentally and theoretically the self-focu...

High polarization selective Si/SiO2 mid-infrared sub-wavelength grating mirrors with large bandwidth adapted to VCSEL integration are compared. These mirrors have been automatically designed for operation at \lambda = 2.3 $\mu$m by an optimization algorithm which maximizes a specially defined quality factor. Several technological constraints in rel...

A high reflectivity and polarization selective high contrast grating mirror has been designed with the use of an automated optimization algorithm. Through a precise study of the tolerance of the different lengths of the structure, the robustness with respect to the fabrication errors has been enhanced to high tolerance values between 5 % and 210 %....

A tolerant GaAs HCG design has been optimized for a mid-IR VCSEL application through the use of an optimization algorithm. Reflection spectra of an experimental grating are in a correct agreement with the simulations.

We present the design of a Si/Si₃N₄ subwavelength grating mirror optimized for an integration in mid-infrared VCSEL. The definition of a quality factor adapted to VCSEL requirements and maximized by an optimization algorithm allowed us to obtain a polarization selective and high reflectivity structure. The robustness with resp...

This paper reports an experimental study of the self-focusing process in iron doped indium phosphide at an 1.06 micron wavelength, identifying the influence of temperature, beam intensity and background illumination \RefereeOne{for two different iron dopings}. We point out that the iron ionization ratio is at the origin of different qualitative beh...

Several designs of sub-wavelength grating mirrors adapted to mid-infrared operation are reported with several percents of tolerance for the grating fabrication. These designs have been automatically optimized by the use of a genetic-based algorithm to maximize a quality factor defined to meet the requirements of a VCSEL cavity mirror. These mirrors...

We solve the photorefractive set of equations by finite difference methods to determine photorefractive quantities. In a second stage, a multi-scale expansion is used to obtain a simple model able to reproduce photorefractive phenomena.

InterCell is an open, operational software suite for implementation, code generation and interactive simulation of fine grained parallel computational models. This article describes the software architecture, some use cases from physics and cortical networks as well as first performance measurements.

Undoped and Fe-doped (0.35, 0.5 and 0.7 at% Fe) LiNbO3 single-crystal fibers were grown using the micro-pulling-down method with resistivity heating. The fibers chemical homogeneity was examined with electron probe micro-analysis and crystallographic orientation was checked with Raman spectroscopy. The engraving of an optical waveguide in a Fe-dope...

Cours d'électromagnétisme

Optical Phase Conjugation is a third order non linear peculiar phenomenon occurring in many non linear crystals. Its principles and applications are reviewed.

This is a basic lecture on photorefractivity: its principle as a low power optical non linearity are shown and applications are reviewed

Ce cours aborde les fondamentaux des mathématiques numériques, outil indispensable au physicien lorsqu'il veut mettre ses modèles en oeuvre. Après un prélude indispensable sur le maniement des ordinateurs, seront abordés entre autres la résolution des systèmes linéaires et non linéaires, les méthodes d'optimisation et d'approximation ainsi que les...

In this lecture, the principles of Optical Second Harmonic Generation in Non Linear second order crystals is explained, along with other second order Non Linearities. Applications are then presented.

After a brief introduction to polarization optics, this lecture reviews the basic formalisms for dealing with it: Jones Calculus for totally polarized light and Stokes parameters associated to Mueller Calculus for partially polarized light.

Photoinduced waveguides are generated by lateral illumination of photorefractive strontium barium niobate. The light-induced waveguides show a complex dynamic relaxation upon removal of the sustaining voltage, which can be exploited for deflecting or modulating the guided wave. The deflection distance easily exceeds 100 μm in a 1 cm long crystal. T...

This paper extends the existing theory of two carrier photorefractivity resonance, which is generally applied to Iron doped Indium Phosphide (InP:Fe), to the case of low non-harmonic illumination. The space charge field profile is computed, and the variations of its amplitude, width and position are determined as functions of the background intensi...

This paper present new experimental and theoretical result concerning the temporal dynamic of the self focusing process, proving that it is characterized by two time scales: one on the order of microseconds, the other on the order of milliseconds. A four quadrants position detector was used to characterize the beam's temporal evolution after propag...

This paper reports the engraving of an optical waveguide inside a LiNbO3 crystal fiber via the photorefractive effect and an optical vortex. Afterwards this waveguide was successfully tested and its properties evidenced.

Lithium niobate (LN) crystal fibers represent promising new substrates for optical applications. Indeed, additionally to the numerous properties of LN, the high length-to-width ratio of LN crystal fibers can be very useful for numerous optical applications. Furthermore, the growing methods used to produce these fibers allow to control their composi...

Light induced waveguides produced by lateral illumination of a hotorefractive crystal show a complex dynamic evolution upon removal of the sustaining applied electric field. Using this effect, deflection and modulation of the guided light is realized by taking advantage of the screening and counter-screening of the space charge distribution. The sp...

Self-trapping of optical beams in photorefractive (PR) materials at telecommunications wavelengths has been studied at steady state In insulators such as SBN [1] and in semiconductor InP:Fe [2], CdTe [3]. PR self-focusing and soliton interactions in semiconductors find interesting applications in optical communications Such as optical routing and i...

The experimental observation of photorefractive self focusing in Sn(2)P(2)S(6) : Te bulk crystals at 1.06 mum wavelength is presented. Steady state self focusing is reached as fast as 15 ms for an input peak intensity equal to 160 W/cm(2). Self focusing is maximum for input peak intensities around 15 W/cm(2) and is decreasing for intensities below...

Temporal and spatial dependency of photorefractive self focusing in InP:Fe from intensity and temperature is compared to a theoretical model; self focusing and bending occur on a microseconds timescale for low beam intensities.

The dynamic creation of waveguides in photorefractive Sn2P2S6 is investigated in the case of a lateral properly shaped illumination, as well as in the case of a longitudinal soliton-like propagation of a self-focused near-infrared wave. It is shown that in this crystal lateral visible light can induce efficiently one-dimensional waveguides by means...

The experimental observation of photorefractive self focusing in Sn2P2S6 : Te bulk crystals at 1.06 μm wavelength is presented. Steady state self focusing is reached as fast as 15 ms for an input peak intensity equal to 160 W/cm2. Self focusing is maximum for input peak intensities around 15 W/cm2 and is decreasing for intensities below and above t...

Photorefractive (PR) spatial soliton propagation hints that all optical routing can be achieved through soliton interactions. This requires, however, fast build up and sensitivity to telecommunication wavelengths. We have investigated the build up of infrared (1,06m) photorefractive solitons in iron doped indium phosphide (InP:Fe) and shown that PR...

We theoretically and experimentally report on fast self-focusing of light in a photorefractive semiconductor. In these applications, semiconductor materials are very attractive considering their high sensitivity at telecommunication wavelengths (1.55 mum), short response time and memory effect. Photorefractive self- focusing and soliton interaction...

Tin hypothiodiphosphate (SPS) is a wide band gap semiconductor ferroelectric that has interesting properties for photorefractive (PR) applications such as high two wave mixing gains, large transparency window coupled with a fast response time and a large electro-optic coefficient. Taking into account all SPS characteristics, its behavior is investi...

This paper shows experimental evidence of photorefractive steady state self-focusing in InP:Fe for a wide range of intensities, at both 1.06 and 1.55 μm. To explain those results, it is shown that despite the bipolar nature of InP:Fe where one photocarrier and one thermal carrier are to be considered, the long standing one photocarrier model for ph...

Steady state photorefractive (PR) self focusing experiments in InP:Fe have been performed with the goal of identifying its potential for creation of self induced optical waveguides and subsequently using it for all optical routing applications. The temporal evolution of the PR related effects in the near IR using a beam focused to a 25 mum waist on...

This paper introduces a research project and a software environment to speed up and size up problem modeling with Partial Differential Equations (PDE). These PDE are defined from a \Mathematica interface, and are automatically solved by a devoted cellular automata program generated to be run on mainframes, clusters and Grids. Moreover, an interacti...

L'amélioration des systèmes optoélectroniques actuels passe par l'intégration de fonctions ”génération” (source laser) et ”traitement” (modulateur EO, cellule de Pockels, convertisseur de fréquence,...) sur un même substrat. Plusieurs techniques d'intégration existent. Elles se répartissent en deux voies. La première consiste à assembler en cascade...