Polariton lasing and Bose-Einstein condensation in an electrically pumped system

We propose to demonstrate the first electrically injected polariton laser. The physics underlying the operation of the laser, and the factors which lead to its optimum performance will be determined. The polariton laser is a new device concept which holds the promise of very low threshold coherent light emission, at the same time as corresponding to non-equilibrium Bose-Einstein condensation (BEC) in a solid state system. The strong coupling between excitons and photons in semiconductor microcavities leads to the formation of novel quasi-particles, exciton-polaritons. Such polaritons exhibit characteristic bosonic properties such as macroscopic occupation of individual quantum states and BEC in a system with long temporal and spatial coherence. Due to the photonic component of the polaritons, the macroscopically occupied polariton state emits coherent light, and forms the basis of a new type of light source, the polariton laser, in which coherent light is emitted without the need for population inversion. Until very recently nearly all work in this field has been carried out under conditions of optical excitation. From the device perspective, new impetus has been given by our recent observation of light emission from polariton states under electrical injection, followed very soon after by two other groups. This proposal aims to capitalise on our recent achievements and overall expertise in the field, to realise an important world first, the first electrically injected polariton laser, as required for real world applications of these novel devices.

Our proposal has major potential for short, medium and long term impact. In the timescale of the programme the outcomes are likely to be of particular significance to researchers in the field, as summarised in the section on Academic Beneficiaries. The effectiveness of the dissemination to these beneficiaries will benefit strongly from our highly effective publication record in major journals, frequent invited and contributed talks at conferences, and past, present and future membership of several European collaborations in the polariton field. Further details are given in the Academic Beneficiaries section. In the longer term, the research is likely to be of very considerable significance in two applications directions. Firstly once its feasibility in GaAs-based structures is established in our programme, the basic ideas will be ready to be transferred to the more challenging GaN-materials system which has the material properties required for operation at room temperature. Such devices will operate in the blue and ultraviolet spectral regions. Main application areas are likely to be as low threshold light sources for data storage and printing applications where potential markets are huge in the $B range for e.g. next generation blu-ray etc. Based on past technological records, it is likely to take 5-15 years from first demonstration to real world exploitation. It is important that the feasibility of polariton laser action that we aim to demonstrate will play a critical role in providing the basis for transfer of the technology to wide band gap materials. Much of the basic technology for GaN vertical cavity emitters was put in place during the Framework 6 EU programme Stimscat which we coordinated. This programme included several of the major European laboratories engaged in GaN materials technology, including notably Sharp Laboratories of Europe. This programme established close links with workers at Sharp; these interactions will continue throughout the duration of the present project, as indicated in the letter from Sharp. We will keep Sharp well informed of progress we make, by holding annual meetings with them to update them on progress, and forwarding copies of publications to them. The associated industrial partners of the FP7 Training Network Clermont4, who include Sharp and also HORIBA, Hitachi Cambridge Laboratory, Finmecchanica, LUXTALTEK will provide further dissemination routes to industry through the annual meetings of all partners. The achievement of the world's first polariton laser has potential to generate significant publicity, and hence to be brought to the attention of a wide spectrum of industries. Following publication, the results will be advertised through trade magazines in the field, and the university of Sheffield press office, as well as dissemination routes through publication in high quality journals. The second area of application is in the area quantum information technology where the electrically injected polariton condensates have potential to be exploited as micron-scale alternatives to atomic condensates for quantum computation schemes. These topics are likely to be of main interest to academic groups for the foreseeable future. More details are thus given in the Academic Beneficiaries section.