Analyse de la structure locale et propriétés optiques de semiconducteurs nitrures pour le développement des diodes électroluminescentes efficaces au-delà du vert.

Abstract : InGaN/GaN quantum wells show the highest known emission efficiency in UV-blue and the current challenge is to push to longer wavelengths. This would be possible by increasing the indium composition but the challenge becomes how to handle the resulting strains. This work has combined transmission electron microscopy and Xray diffraction in order to determine the relaxation rates, the local chemical composition and defects formation in these systems. The results show that there are no composition fluctuations in these InGaN layers where the indium content was around 20%. Therefore, the differences in emission may be explained by the changes in quantum wells thicknesses and/or the presence of defects. Indeed, several types of defects have been observed and characterized, such as pinholes or planar defect domains. For InGaN/GaN quantum wells with strain compensating AlGaN layers, Xray diffraction showed that, when the AlGaN layer thickness increases, keeping constant the spacing between InGaN layers (around 16-17 nm), the quantum wellsare totally strained in and out the growth plan. Using transmission electron microscopy, it is shown that the relaxation occurs through the formation of domains as well as a type dislocations. The dislocations propagate from the quantum well tothe surface and the density of the defects increases with the thickness of the AlGaN layers.
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Nicolas Chery. Analyse de la structure locale et propriétés optiques de semiconducteurs nitrures pour le développement des diodes électroluminescentes efficaces au-delà du vert.. Physique [physics]. Normandie Université, 2018. Français. ⟨NNT : 2018NORMC265⟩. ⟨tel-02156758⟩

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