Researchers in the field of optoelectronics have taken major steps towards building whole devices from phase-changing chalcogenides.
These materials promise to bridge the gap between glasses such as fibre optics and semiconductors such as silicon — potentially resulting in faster data streaming and more efficient solar cells, among many other applications.
‘With chalcogenides we can form the material into fibres, thin films, microspheres, nanophotonics — anything that you can make glass in to, but they also have the electronic properties of semiconductors, so it’s almost a marriage of the two worlds,’ said Prof Dan Hewak, of Southampton University, who leads a team aiming at building new devices.
Chalcogenides, which are based on sulphur, selenium or tellurium, have been used as thin films for niche applications such as rewritable optical discs and non-volatile memory devices for a number of decades now.
But to realise their full potential as semiconductors, as well as optical materials, they must be doped to control certain properties of the material through a process called ion implantation, which the team has recently demonstrated. Immediate applications would likely be in the field of telecommunications, Hewak explained.
‘The world is criss-crossed with optical fibres made from silica glass — a relatively inert, passive material that just moves light from one place to another — but by making our optical fibres from these chalcogenides, we have a much more active material that could change properties easily.
‘It would mean faster connections, because the switching speeds are much faster, as well as less bottlenecks, because you don’t need repeaters and amplifiers,’ he said.
Other devices that may benefit from chalcogenides include LEDs, photodiodes, photovoltaic cells, optical amplifiers, switches, logic gates and memory cells.
Indeed, some newer photovoltaic cells, claiming greater efficiencies, are starting to use chalcogenides in the p-type electrode (with an oxide for the n-type), although Hewak says even greater efficiencies could be achieved if the whole structure were made from chalcogenides.
‘The electronics industry is very conservative and to introduce a new material it has to be multifunctional and there has to be a pretty good reason to replace what’s currently in the fab lines.
‘They’re not going to just change the materials and the way they process them for a few small applications — we need to have widespread applications for chalcogenides [in order for them] to be introduced by companies such as Intel and STMicroelectronics.’
Hewak’s team is collaborating with researchers from Cambridge and Surrey universities and the project has just received £1.48m from the EPSRC.