A successful EU funded research training network, co-ordinated by Prof. Kevin
O’Donnell, recently reached its end with the final meeting hosted at Strathclyde
University and Ross Priory. The RENiBEl network incorporated seven university
laboratories and directed the research efforts of over 50 scientists on the
fundamental materials issues underlying prospective Rare Earth-doped GaNbased light emitting devices. The number of e-mails in Kevin’s RENiBEl mailbox
reached more than 3400 items, with more visible evidence of success coming in
a series of high quality publications and conference presentations.
For example, a series of papers describing innovative work based on the use of
very-wide gap semiconductors in conjunction with the more conventional gallium
nitride (GaN) have had significant impact. We first demonstrated that covering
the GaN host material with thin aluminium nitride (AlN) cap layers had dual
benefits of allowing more than an order of magnitude increase in luminescence
intensity as well as greatly reducing damage induced during ion-implantation [1].
The brighter samples developed in this way allowed us to identify, for the first
time, additional fine structure in the luminescent spectra from Europium (Eu) ions
in GaN and confirm the existence of multiple luminescent sites for Eu [2]. This
work proved to be very relevant in explaining the behaviour of red GaN:Eu lasers
developed at Cincinatti. A more wdiely ranging invited presentation on the topic
of site multiplicity of rare earth ions in III-nitrides at the MRS Fall meeting in
Boston led to an Outstanding Paper Ribbon Award [3]. Failure mechanisms in
the AlN-caps during annealed at ultra high-temperature were investigated and
gave indications of how to improve their functionality [4].
The work has developed to investigate the use of the little-studied Aluminium
Indium Nitride alloy (grown at the Institute of Photonics for related joint projects
with Physics, including two new EU-funded projects) as a wide-gap host for
luminescent Rare-Earth ions. Throughout the project the work has involved close
interaction with theorists, including Ben Hourahine (now of this Department) [e.g.
5] and extensive use of facilities such as the Daresbury synchrotron and the
Department’s electron microscopes.
The strong and productive relationships cemented during the project have made
it very natural for continuing close collaboration of some of the groups involved
and further research opportunities are plentiful. Already on the horizon is
“Renibel – The Book” and who knows, next could be The Movie.
1. K. Lorenz, U. Wahl, E. Alves, S. Dalmasso, R.W. Martin, K.P. O'Donnell, S.
Ruffenach and O. Briot, Appl. Phys. Lett. 85, 2712 (2004)
2. K. Wang, R.W. Martin, K.P. O'Donnell, V. Katchkanov, E. Nogales, K. Lorenz,
E. Alves, S. Ruffenach, O. Briot, Appl. Phys. Lett. 87, 112107 (2005)
3. K.P.O’Donnell, V. Katchkanov, K. Wang, R.W. Martin, P.R. Edwards, B.
Hourahine, E. Nogales, J.F.W. Mosselmans, B. De Vries, and the RENiBEl
Consortium, MRS Symp. Proc. 831, E9.6 (2005)
4. E. Nogales, R.W. Martin, K.P. O´Donnell, K. Lorenz, E. Alves, S. Ruffenach
and O. Briot, Appl. Phys. Lett., 88, 031902 (2006)
5. S. Petit, R. Jones, M. J. Shaw, P. R. Briddon, B. Hourahine, T, Frauenheim.
Phys. Rev. B 72, 073205 (2005)