Computers form the backbone of modern society and the digital economy. However, since 2010 CPUs have reached the maximum speed they can practically sustain - limited by the intrinsic loss in electrical wires. To overcome this limit, electrical wiring must be replaced by optical wiring, while continuing to use the mature silicon technology platform.
The Holy Grail of silicon photonics is a light source that can be easily incorporated into the standard silicon fabrication process as silicon itself is a poor light emitter due to its indirect bandgap. The currently favoured industrial solution is to mount efficient light emitters such as III-V semiconductors on silicon, but this approach is rather expensive and complicated. To succeed in mass markets, silicon photonics requires new low-cost light sources that can be easily integrated on chips.
One can easily identify the requirements of the required light emitting material: it should have a direct band-gap of around 1 eV, type-I band alignment to Si, be composed of low-cost and earth-abundant elements, and be suitable for mass production (meaning that good light emission should be retained for polycrystalline films obtained through low-cost and scalable deposition processes such as close-space sublimation). No existing material can meet all of these requirements.
Recently, sesqui‐chalcogenides (i.e. X2Y3 where X=pnictogen such as Sb, As and Bi and Y=chalcogen such as S, Se, Te) have emerged as a class of materials that can satisfy many of these requirements. Sb2Se3 for example has shown exceptional performance in solar cell applications (reaching 10% efficiency in only a few years). Sesqui‐chalcogenides are also showing great promise for other applications including thermoelectrics, phase change memories and topological insulators but their potential for on-chip light emission is so far unexplored.
In this joint theory and experimental project you will use predictive first principles materials modelling (density functional theory) to screen different sesqui‐chalcogenide compositions to identify candidate materials with the required stability and electronic properties. Thin films of these compositions will then be produced and characterised using absorption and photoluminescence measurements, as well as the refractive index and crystallinity of the thin films using ellipsometry, AFM and SEM. In the second half of this project, you will combine the optimised material with silicon devices to make light emitting diodes to test their suitability for optical communication.
3 year PhD with 3.5 years tuition fees plus stipend (£15,009 for 2019/20).
This project will be advertised until a suitable candidate is found.