Research

My research in Exeter is about the doping of semiconductors (in particular GaN) with rare earth (in particular Erbium (Er)).

Rare earth are very interesting for doping semi-conductors because of their f electron shell that have a really special behavior. The f shell is very contacted in rare earth and is shielded by the valence electrons. Then, the electronic transitions that are possible in between the f-shell are very weakly dependant of the surrounding of the rare earth. It the rare earth electronic transition can be exited they will induce the emission of light at a given wave length that is do not dependant of the surrounding. The depending of the excitation it is possible to produce infra-red light or visible light of different colors. In particular Er shows transition in the infra-red at 1.52 mm that corresponds to the minimum of adsorption of optic fiber, that is very suitable for opto-electronics.

Further more the use of rare earth could also be a way to produce light with indirect semi-conductors (like Si) that cannot produce efficiently light. Then, part of my research is focused on understanding the structures than can give this light production in Si.

Structure of Erbium defect in Si

Er co-doped with oxygen has shown some huge increase of the light emission at room temperature. Unfortunately, the interaction and structure that Er and O form in Si are still not very well known but nevertheless are fundamental to understand how to get an efficient light emitter.

Er-O structure in Si

Structure of Rare Eaths in GaN

The doping of hight gap semiconductor GaN with rare earth is a way to produce efficient visible light emitter in particular around the blue color that would be valuable both to produce laser for high density information storage or simply to create array diodes for flat sceens. Nevertheless, the behavior of rare earth inside GaN is not very well known. The understanding of the local Er structure that can give rise to an efficient light emission is fundamental.

Rare Eaths defects interaction in GaN

Early calculation have shown that Rare Earths (RE) alone in GaN are electriacally inactive. We are then investigating the RE-defects complex in GaN that can induce efficient energy transfert to the RE and then gives a good light production yield. It finally should be possible to define the proper condition of growth and impurities from first principle calculations.

Er in GaN

You can find here the last talk I gave at the E-MRS Strasbourg (2003) for more detailed informations

The Exter physics theory group.

Contact: Jean-Sebastien Filhol (filhol@excc.ex.ac.uk)

Last revised: 25/08/2003