Application de la technique des oscillations d'intensité de diffraction électronique en incidence rasante à la croissance des semi-conducteurs III-V par épitaxie par jets moléculaires

Reflection high energy electron diffraction (RHEED) oscillations recorded during molecular beam epitaxy (MBE) allows the determination in real time of some of the main growth parameters of III-V semiconductors such as growth rate, element III fluxes impinging at the surface and sticking coefficients of the elements III. Illustrations of this technique are given for GaAs, AlAs, Al(x)Ga(1-x)As and Al(1-x)In(x)As epitaxial growth onto GaAs substrates. The growth interface roughness for these different materials is investigated versus growth parameters. We also report for the first time the observation of RHEED oscillations phenomenon during the growth of Ga(1-x)In(x)As and Al(1-x)In(x)As lattice matched on InP substrates.L'enregistrement des oscillations d'intensité de diffraction des électrons en incidence rasante (RHEED) en cours de croissance épitaxiale par jets moléculaires (EJM), permet la détermination en temps réel de certains paramètres essentiels de la croissance tels que vitesse, composition d'alliage, intensité des flux d'éléments III incidents à la surface et coefficients de collage des éléments III. Nous donnons des exemples de l'utilisation de cette technique obtenus dans le cas de la croissance de GaAs, AlAs, Al(x)Ga(1-x)As et Al(1-x )In (x )As sur substrats GaAs. Nous discutons des états de rugosité de l'interface de croissance observés pour ces différents matériaux et de leurs évolutions en fonction des paramètres de croissance. D'autre part, nous reportons l'observation pour la première fois du phénomène des oscillations de RHEED pendant la croissance Ga(1-x)In(x)As et Al(1-x )In(x)As en accord de maille sur substrat InP

Epitaxial YBa2Cu3O7-8/SrTiO3 heterostructures grown by pulsed laser deposition for voltage agile microwave filter applications

The performance of tunable microwave devices based on heteroepitaxial YBa2Cu3Ox/SrTiO3 films on (001) LaAlO3 substrate has been evaluated. It has been ascertained that 'out-of-plane' SrTiO3 lattice parameter is the relevant factor in determining both the agility and dielectric loss of the SrTiO3 layers. After high temperature annealing (1100 °C, 1 atm O2), only SrTiO3 layers deposited under low oxygen pressure (∼ 10-5 Torr) show an appreciable reduction of the dielectric losses whilst maintaining high agility. Annealed samples exhibit voltage independent losses of ∼ 5.10-3 simultaneously with 55% dielectric agility at 6 GHz and 77K

KINETIC ANALYSIS OF THE CATALYTIC DECOMPOSITION OF HYDRAZINE

The bond-order conservation method was used to study the catalytic decomposition of N2H4. Variation in the activation energy, E, of the most relevant steps was calculated as a function of the enthalpy of adsorption of N, QN, between 0 and 1250 kJmol-1. Results suggest that below QN = 520 kJmol-1 the catalytic decomposition of N2H4 produces mostly N2 and H2. Above QN = 520 kJmol-1, NH3 and N2 are the main products. Near QN = 520 kJmol-1 N2, H2 and NH3 are obtained, in agreement with experimental results on different metals