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Through thick and thin: our work with chalcogenide materials, thin films and devices
Professor Daniel W.Hewak
Interest in chalcogenide materials has, over the last decade, increased significantly as glasses, crystals and alloys find new life in a wide range of modern devices. Many of these applications require chalcogenide films, from nanometer to millimeter thicknesses, to exploit the functionality of this material family; however there are other geometries, notably optical fibre, microspheres, nanoparticles and nanowires which are of great interest. Our own research in this field has concentrated on amorphous chalcogenides formed with new compositions based on gallium and/or germanium sulphides. Through modification of this relatively unknown family of chalcogenides, new compositions with new and desirable properties were synthesized. These glass forming groups offer an alternative to the better known arsenic- or selenium- or tellurium- based glasses, providing lower toxicity, higher melting temperatures as well as the ability to be modified with a wide range of dopants including rare earths, transition and precious metals.
In this talk we discuss our work with chalcogenide materials and how it has progressed and evolved since the early 1990s. Our initial research activities focused on optical fibre for telecommunications applications, which lead to new methods for purifying and synthesizing chalcogenide glasses and insight into glass formation and crystallization. As time went by, interest expanded to mid-infared applications and longer wavelengths at which conventional optical materials do not transmit. Through rare earth doping, we identified twenty-one fluorescent transitions with peak emission wavelengths longer than 2 microns, seven of which have not been reported in a glass before. This work has paved the way for the first chalcogenide glass lasers, demonstrated in both bulk and optical fibre form.
By the late 1990's work expanded to thin film devices and a variety of techniques were adapted to achieve our desired thick and thin chalcogenide films. We currently exploit several deposition methods; chemical vapor deposition, inverted hot dip spin coating, sputtering, evaporation and pulsed laser deposition are now routinely used. These techniques allow the deposition of films ranging in thickness from several nanometers to hundreds of microns. The initial driving force behind our thin film work has been the realization of planar optical waveguides for optical integrated circuits. This now encompassed thinner films for phase change memory devices, an application where our efforts once again return to new material discovery.
Finally, our more recent activities in new geometries is described, in particular the first demonstration of chalcogenide glass microspheres. Micro-resonators have attracted considerable attention as a potential geometry for photonic devices with application including multiplexing, memory and switching.
The exploitation of chalcogenide materials has evolved over the last two or three decades from a simple infrared transmitting bulk glass into a multifunctional optoelectronic material for the future. We hope that with this talk you will see our own small role in this evolution and share in our excitement for these materials in the future.
6th International Workshop on Nanophotonics Taiwan 10 Mar (2008)
Copyright University of Southampton 2006