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Séminaire général de l’INSP

Exploration of intrinsic properties of wide-band-gap materials - Naoki Ohashi - Vendredi 26 juin à 16 h 30

INSP - 4 place Jussieu - 75252 PARIS Cedex 05 - Barre 22-23 - 3e étage, salle 317

Naoki Ohashi - National Institute for Materials Science (NIMS), Tsukuba, Japan


We can find a lot of electronic devices utilizing wide-band-gap materials (WBGMs). For instance, blue LED has been achieved by development of nitride semiconductors, and many mobile electronic devices have been developed by miniaturization of not only silicon LSIs but also passive electronic components made from oxides. Although technology for fabrication of those devices has been developed, we have not answered some fundamental questions on physics and chemistry in WBGMs. For instance, we are not very sure if the observed conductivity in nominally undoped WBGMs is caused by their intrinsic/native defects or extrinsic unintentional impurities there.

Now, my group is paying attention to hydrogen impurity in WBGMs. As quantitative analysis of hydrogen impurity in WBGMs is very tough, many scientists and engineers have shut their eyes to hydrogen impurity in WBGMs. However, it seems that hydrogen impurity plays a lot of roles in solid state materials. In this seminar, activity of our group on defects and hydrogen impurities in oxides, such as ZnO, SnO2 and SrTiO3, will be introduced. In particular, some results obtained by mass spectrometry on isotope enriched samples and interpretation of the observation utilizing DFT calculations will be presented.

Another remained question in WBGMs systems is structure and properties of surfaces and interfaces. As many WBGMs are used in functional ceramics, grain boundaries in ceramics have been extensively investigated. However, even the mechanisms behind the functions of commercially available ceramics are unclear. To solve those remained questions, preparation of simplified oxide interfaces for modeling and analysis of their essential properties have been conducted in our group. At this seminar, some results utilizing hard-x-ray XPES on oxide interfaces will be presented.


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