Applications are invited for a post-doctoral researcher in condensed matter
theory to join a major programme funded by Science Foundation Ireland to 
investigate the fundamental properties of future photonic materials and devices. 
As part of that project, we have developed tight-binding and envelope 
function models which lead understanding of the electronic and 
optoelectronic properties of extreme semiconductor alloys such as 
GaNxAs1-x. GaNAs is an example of a novel class of semiconductor alloy 
where substitutional N atoms introduce an exceptional reduction in energy 
gap and many unusual band structure features. The current post aims to 
develop a wider understanding of the electronic structure of extreme alloys,
and also to investigate the consequences of the novel electronic properties
for a range of applications, including low-noise avalanche photodiodes, 
terahertz electronics and long wavelength semiconductor lasers.

The main focus of this position is centred on extreme semiconductor alloys
such as GaInNAs, both to understand their novel electronic structure and 
also to identify how the electronic structure can be engineered for 
applications. 

The project will focus on two research topics:

The incorporation of N is one of the most promising routes to achieve 1.5 m
quantum dot emission on a GaAs substrate. However it also brings additional
challenges to the growth and material uniformity. We anticipate that the 
random distribution of N atoms in a GaInNxAs1-x QD can lead to significant
inhomogeneous broadening of the QD energy levels. Each dot will typically 
contain ~105 atoms in total, implying ~103 N atoms per dot for x ~1%. Our
previous work on GaNAs has shown that even a random distribution of N 
atoms leads to inhomogeneous broadening, due to the influence of the small
number of N cluster states expected in such alloys. We shall investigate 
the influence of composition and of statistical fluctuations in cluster 
number both on the maximum emission wavelength  which can be achieved in 
GaInNAs pyramidal QDs to be grown at Tyndall, and also on the variability 
in emission wavelength between nominally identical dots. We shall undertake
 envelope function calculations including details of the N atom 
distribution to determine how N clusters affect the state symmetry and 
matrix elements in individual QDs, and to what extent the N clusters lead
to a reduction in matrix elements and breakdown of k-selection rules. We 
are uniquely placed with our models for dilute nitride alloys and for QD 
band structure to contribute both to the development of GaInNAs QD growth
and also to place clear requirements on that growth and the engineering of
inhomogeneous broadening both for single photon sources and for laser and
optical amplifier applications. This will strongly support the overall 
establishment of a leading growth capability in Tyndall.

The band structure models we have developed for dilute nitride alloys are 
of relevance also to understand a range of other extreme alloys, including
GaBiAs and II-VI materials such as ZnOS and ZnOSe. Initial calculations
and measurements show that the behaviour of GaBiAs is similar to that of 
GaNAs, with a similar band-gap bowing, but the band-gap bowing being due to
Bi resonant levels in the valence  band, rather than N states in the 
conduction band. We now wish to extend these calculations, to develop a
more general model of extreme alloys, including a detailed understanding
of the unusual alloy system GaBiAs and of its potential benefits relative
e.g. to GaInNAs for low-noise avalanche photodiodes, terahertz electronics
and long wavelength semiconductor lasers. The general understanding 
dveloped will be tested against experimental measurements carried out 
by collaboratots and in the literature, and will be of relevance to the
wider description of extreme semiconductor alloys, including wide-gap 
materials such as ZnOS and ZnOSe which are of increasing interest due to 
their novel growth modes, large exciton binding energy, and general 
potential as UV sources, detectors and protective coatings. 

The successful candidate should already have a PhD in physics or a related
discipline, with a strong research record in computational modelling. 
Applications must include:
1. Full CV, including list of publications; 
2. Rsearch statement, outlining research achievements, interests and plans; 
3. Copies of two recent published papers.

Informal enquiries regarding the position can be made to Professor Eoin O' 
Reilly (Tel. +353 (0)21 490 4413, email: eoin.oreilly:tyndall.ie.

Further details: www.tyndall.ie/ptg

Please submit a CV to careers:tyndall.ie, quoting the reference number.