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We report on the structural and electrical properties of epitaxial SmN thin films grown by molecular beam epitaxy. The effect of the growth temperature and nitrogen precursor, either pure molecular N2 or NH3 was investigated. The structural quality of SmN was assessed by X-ray diffraction and the epitaxial growth character is observed over the entire range of growth temperatures, from 300°C to 800°C, with both nitrogen precursors. The highest quality films are produced at a growth temperature of about 430°C by using N2 as a nitrogen precursor. Hall Effect and resistivity measurements establish that SmN films are heavily n-type doped semiconductors, suggesting the presence of nitrogen vacancies, a recurring phenomenon in rare earth nitride compounds.
GdN/SmN based superlattices have been grown by molecular beam epitaxy. In-situ reflection high energy electron diffraction was used to evaluate the evolution of the epitaxial growth and the structural properties were assessed by ex-situ X-ray diffraction. Hall Effect and resistivity measurements as a function of the temperature establish that the superlattices are heavily n-type doped semiconductors and the electrical conduction resides in both REN layers, SmN and GdN.
We present an overview of our work concerning the fabrication of GaN-based microcavities grown on silicon substrates dedicated to the observation of the strong light-matter coupling regime. In the view of recent promising results in the field, prospects regarding the improvement of heterostructures in order to observe room temperature polariton lasing from a GaN-based microcavity grown on a silicon substrate will be discussed.
During the last ten years, we have developed an efficient growth process of nitrides on silicon substrates by molecular beam epitaxy. In collaboration with partners AlGaN/GaN HEMTs on Si having promising performances have been fabricated. Focusing on the growth aspect and underlying some of the key issues, we present in this paper an overview of our contribution in the field of AlGaN/GaN HEMTs on Si substrates.
We have studied the influence of a deuterium diffusion on the electrical characteristics of the 2D gas present in AlGaN/GaN heterostructures. The deuterium diffusion is performed by exposing the structures to a rf remote deuterium plasma. We find that both the sheet carrier concentration and the electron mobility decrease and that these effects are partly reversible under thermal annealing. These results suggest that deuterium behave as acceptors in the 2D gas region. The negatively charged deuterium act as additional scattering centers for electrons.
Language tools that help people with their writing are now usually
included in today's word
processors. Although these various tools provide increasing support to
native speakers of a
language, they are much less useful to non-native speakers who are
writing in their second
language (e.g. French speakers writing in English). Real errors may
go undetected and
potential errors or non-errors that are flagged by the system may
be taken to be genuine errors
by the non-native speaker. In this paper, we present the prototype of
an English writing tool
which is aimed at helping speakers of French write in English. We first
discuss the kind of
problems non-native speakers have when writing in a second language. We
then explain how
we collected a corpus of errors which we used to build a typology of
errors needed in the
various stages of the project. This is followed by an overview of the
prototype which contains
a number of writing aids (dictionaries, on-line grammar helps, verb
conjugator, etc.) and two
checking tools: a problem word highlighter which lists all the
potentially difficult words that
cannot be dealt with correctly by the system (false friends, confusions,
and a grammar
checker which detects and corrects morphological and syntactic errors.
describe in detail
the automata formalism we use to extract linguistic information, test
and detect and correct errors. Finally, we present a first evaluation of
the correction capacity
of our grammar checker as compared to that of commercially available systems.
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