Opto-electronics Research

Activity Leader:  Professor Kevin Homewood

The main research activity is the ongoing programme on efficient light emission from silicon light emitting diodes (LEDs).  The approach being followed is the application of dislocation engineering (DE) to achieve efficient silicon LEDs, using entirely ULSI compatible technology - ion implantation and standard dopants (see Figures 1 & 2.). Decoupling of the radiative recombination routes from non-radiative recombination in the bulk and at the surface, using dislocation loops as potential barriers, enables high temperature operation to be achieved.   The basic device emits at 1.16 microns at the lower wavelength end of the extended telecommunication band.  The use of optically active dopants in the active region of this device enables the emission wavelength to be tuned.  For example to the important 1.55 micron band.  

	Figure1.  A standard dislocation engineered silicon LED.  The dislocation loops shown as green discs are introduced using the standard Boron doping implant
	Figure 2.  Band diagrams of conventional and dislocation engineered (DE) silicon LEDs. In the DE devices the strain barrier introduced using a dislocation loop array prevents onward diffusion of carriers enhancing the radiative emission and providing room temperature operation.

The programme has significant EPSRC funding that is supporting two research fellows.  Two PhD students, are currently working fulltime on this project.

A second activity is in the development of solar cells based on beta iron disilicide.  This material promises efficiencies greater than 20% in a sustainable and non toxic technology.   We have made several recent, and major breakthroughs, first in the discovery of amorphous iron disilicide as a new semiconductor material and the evaluation of its optical properties and secondly in its low temperature synthesis using sputtering techniques, in collaboration with professor John Colligon’s group at the Metropolitan University of Manchester.  We believe that the amorphous form of iron disilicide, synthesised at low temperature, and therefore formed having a low energy budget, is the most promising route to efficient and cheap large area solar cells.  An example of a layer is shown in Figure 3.  Significantly, this technology would utilise environmentally friendly materials, which are fully sustainable.  The next steps are to develop a suitable doping technology for this system.

Figure 3.   Cross sectional TEM image of an amorphous iron disilicide layer deposited at room temperature.  a), b) and c)  are micro-diffraction patternstaken  from the top amorphous layer, the interface region and the silicon substrate respectively.