Etude physique et théorique des matériaux à changement de phase pour disques optiques

Le thème de cette thèse s'inscrit dans l'étude et le développement de la technologie de l'enregistrement optique réversible par changement de phase (technologie des DVD-RAM). La compréhension des phénomènes physiques intervenant dans les processus d'écriture et d'effacement des dommées est aujourd'hui indispensable pour permettre le développement des DVD de demain. La très forte interactions entre les aspects optique, thermique, thermodynamique et cinétique des transitions de phase impliqués dans des systèmes e couches minces nous a conduit à mettre en place des modèles pour chacun de ces aspects puis à coupler ces différents phénomènes dans une simulation globale; celle-ci permettant d'analyser avec précision les mécanismes et les paramètres influençant les processus d'amorphisation et de cristallisation qui régissent respectivement les opérations d'écriture et d'effacement. Cette simulation a été construite à partir d'un support expérimental varié : dépôt de couches minces, caractérisation optique d ces couches, caractérisation structurale : microscopie électronique à transmission, diffraction des rayons X, EXAFS.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Self-Assembled UV Photodetector Made by Direct Epitaxial GaN Growth on Graphene

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Effect of doping on global and local order in crystalline GeTe

International audienceEffect of nitrogen and carbon doping on the structure of GeTe has been investigated using x-ray diffraction and extended x-ray absorption fine structure (EXAFS) spectroscopies. While Bragg diffraction which probes the global structure exhibits a clear transition upon doping from the rhombohedral phase to the cubic (rocksalt) phase, the local structure probed by EXAFS remains rhombohedrally distorted across the compositions studied. The apparent inconsistency between the results of the two techniques used is attributed to disordering upon doping and the resulting order-disorder transition that is “seen” by site-averaging diffraction as a displacive rhombohedral-to-cubic transition

Effect of Al 2 O 3 thickness and oxidant precursors on the interface composition and contamination in Al 2 O 3 /GaN structures

International audienceIn this paper, we investigate the Al 2 O 3 /GaN critical buried interface of the next generation of gallium nitride (GaN)‐based transistors using time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and hard X‐ray photoelectron spectroscopy (HAXPES). Results highlight that gallium oxidation at this interface is enhanced when increasing the Al 2 O 3 thickness from 3 up to 20 nm. Gallium oxidation is reduced when using both O 3 and H 2 O as oxidant precursors, compared with only H 2 O during the growth of Al 2 O 3 . In addition, the O 3 /H 2 O‐based Al 2 O 3 favors a reduction of contaminants such as hydrogen and carbon but enhances the presence of halides (Cl − and F − ) at this Al 2 O 3 /GaN interface

Characterization of GaN structures by a combined SIMS and HAXPES approach

International audienceAmong III-N materials, GaN shows great promise and is already used in the electronic industrybut there are still technological issues to resolve. Consequently, characterization techniquescapable of providing information at the nanometer scale are required in order to meet theindustrial demand of this market. The combined approach of hard x-ray photoelectronspectroscopy (HAXPES) and secondary ion mass spectrometry (SIMS) is an attractive methodto analyse buried interfaces

Laboratory HAXPES of GaN structures for power electronic

International audienceHigh-electron-mobility transistors (HEMTs) based on AlGaN/GaN heterostructures are being developed for high power electronic. The presence of a two-dimensional electron gas (2DEG) at the AlGaN/GaN interface enables reaching high electron mobility (>1500 cm$^2$.V-1.s-1). For safety and reliability reasons, normally-off HEMTs are requested and can be obtained by the full recess approach, based on the removal of the AlGaN layer underneath the gate. The dielectric (Al$_2$O$_3$) and metal gate are directly deposited on the etched GaN surface to create a metal-insulator-semiconductor (MIS) structure, giving rise to the so-called MIS-HEMTs. The final devices properties strongly depend on the quality of the buried Al$_2$O$_3$/GaN interface. Advanced chemical characterization of this critical interface is thus mandatory. Laboratory HAXPES has recently appeared and its use is quickly rising for optimizing technological devices [3]. It is here a promising technique to investigate a more realistic Al$_2$O$_3$/GaN interface, e. g. with a thick Al$_2$O$_3$ layer. We have developed specific protocols to investigate the impact of Al$_2$O$_3$ thickness, precursors and post-deposition anneal on the GaN surface oxidation and stoichiometry

Laboratory HAXPES of GaN structures for power electronic

International audienceHigh-electron-mobility transistors (HEMTs) based on AlGaN/GaN heterostructures are being developed for high power electronic. The presence of a two-dimensional electron gas (2DEG) at the AlGaN/GaN interface enables reaching high electron mobility (>1500 cm$^2$.V-1.s-1). For safety and reliability reasons, normally-off HEMTs are requested and can be obtained by the full recess approach, based on the removal of the AlGaN layer underneath the gate. The dielectric (Al$_2$O$_3$) and metal gate are directly deposited on the etched GaN surface to create a metal-insulator-semiconductor (MIS) structure, giving rise to the so-called MIS-HEMTs. The final devices properties strongly depend on the quality of the buried Al$_2$O$_3$/GaN interface. Advanced chemical characterization of this critical interface is thus mandatory. Laboratory HAXPES has recently appeared and its use is quickly rising for optimizing technological devices [3]. It is here a promising technique to investigate a more realistic Al$_2$O$_3$/GaN interface, e. g. with a thick Al$_2$O$_3$ layer. We have developed specific protocols to investigate the impact of Al$_2$O$_3$ thickness, precursors and post-deposition anneal on the GaN surface oxidation and stoichiometry

Structural and functional properties of Zn(Ge,Sn)N2 thin films deposited by reactive sputtering

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