Advanced materials for organic and hybrid polariton structures and devices

The absorption and emission of light is fundamental to both optoelectronics and biological processes. This process usually takes place in discreet jumps, in which an excited state electron emits a photon as it returns to its ground state, or a photon is absorbed to create an excited state electron. Our growing ability to manipulate light and matter however now allows a different possibility, in which the photon and exciton are 'mixed' together, forming a type of state called a cavity-polariton. Rather than being of simple academic interest, cavity polaritons are a fascinating test-bed for fundamental physics and can have potential applications in ultra-low threshold lasers, on-chip communications elements and new types of quantum-mechanical simulator devices.

Polaritons can be created in an optical structure in which a semiconductor is placed between two highly reflective mirrors. This structure traps photons into a series of discreet optical modes. Within the so-called 'strong-coupling regime' the photons trapped in the cavity can couple with the excited states of a semiconductor within the cavity and form the cavity-polaritons. In this project, the student will develop strong-coupled optical cavities that contain a range of semiconductor thin films and assess their relative lasing threshold following optical excitation. A wide range of materials will be explored, including organic semiconductor dyes and 2-dimensional perovskites, with the objective being the fabrication of polariton lasers that operate at very low thresholds.

The student will be tasked with growth and fabrication of the relevant structures (including deposition of inorganic and organic materials by thermal evaporation, e-beam evaporation and spin-coating). The student will also undertake synthesis of new 2D perovskite materials and will explore means to enhance their light-emission efficiency. The student will also take a very active role in performing optical characterization of all structures fabricated using a range of laser-based spectroscopies.

Our objective is to develop a new photonic platform that will be used as the basis of new low-threshold (low energy) laser devices. Together with colleagues in Southampton, we will explore the use of such devices as physical media that can be used to perform optically-driven calculations. Such systems offer the potential to be able to solve very large computational problems at high speed in a way that could not be achieved by a 'classical' computer. The Impact of such work will be in the realization of new photonic devices that are used in high-speed computation and information processing. There is also relevance for the development of emitting display technologies having enhanced efficiency, or - more speculatively - a means to change molecular pathways in chemical reactions. This may have importance in the development of a new type of 'light-driven' catalysis media.

The project maps onto EPSRC Information and communication technologies ('Optoelectronic devices and circuits, Photonic materials, Quantum optics and information).

The project will be performed together with colleagues at the Universities of Southampton and St. Andrews as part of the EPSRC-funded 'Hybrid Polaritonics' Programme Grant.