An efficient, practical and cost-effective means for directly converting heat into electricity is a very appealing concept. In principle, thermo-photovoltaic (TPV) cells could form the critical component of various systems for generating electricity from different types of heat sources including combustion processes, concentrated sunlight, waste process heat, and radio isotopes. This opens up a wide variety of possibilities for technology uptake and so TPV systems can be envisaged for use in applications ranging from small power supplies to replace batteries, to large scale co-generation of electricity. However, existing TPV cells are based on GaSb and are spectrally matched to heat sources at temperatures of ~1800 oC which limits their practical implementation and widespread uptake. In this project we shall build on existing UK based world class III-V semiconductor materials expertise to fabricate novel low bandgap TPV arrays on inexpensive GaAs substrates, capable of efficient electricity generation from thermal waste heat sources in the range 500-1000 0C commonly encountered in industrial processes. The project will demonstrate the next step towards fabrication of large area TPV arrays essential for the commercial viability of TPV heat recovery, and will enable their widespread implementation in a wide range of high energy consumption industries such as glass, steel and cement manufacture, oil/gas and energy generation.

An efficient, practical and cost-effective means for directly converting heat into electricity is a very appealing concept. In principle, thermo-photovoltaic (TPV) cells could form the critical component of various systems for generating electricity from different types of heat sources including combustion processes, concentrated sunlight, waste process heat, and radio isotopes. This opens up a wide variety of possibilities for technology uptake and so TPV systems can be envisaged for use in applications ranging from small power supplies to replace batteries, to large scale co-generation of electricity. However, existing TPV cells are based on GaSb and are spectrally matched to heat sources at temperatures of ~1800 oC which limits their practical implementation and widespread uptake. GaInAsSb TPV cells with bandgap 0.53 eV have exhibited excellent performance with internal quantum efficiency near 95%. But, currently these are lattice-matched on GaSb substrates making them too expensive for practical implementation except in specialist high value or space applications. TPV development on larger format GaAs substrates will enable effective technology uptake through cheaper volume manufacturing of TPV cells. Consequently, there is a need to transfer the GaInAsSb cell architecture to GaAs. In this project we shall build on existing UK based world class III-V semiconductor materials expertise to fabricate novel low bandgap InGaAsSb TPV arrays on inexpensive GaAs substrates, capable of efficient electricity generation from thermal waste heat sources in the range 500-1500 oC commonly encountered in industrial processes. These monolithic arrays will be validated on-site together with our industry partners at Pilkington and MPIUK (Tata steel). The project will demonstrate the next step towards fabrication of large area TPV arrays essential for the commercial viability of TPV heat recovery, and will enable their widespread implementation in a wide range of high energy consumption industries such as glass, steel and cement manufacture, oil/gas and energy generation.

We aim to achieve a breakthrough in the performance of "dilute nitride" semiconductor materials to enable the development of novel light sources and photodetectors which can operate in the mid-infrared spectral range. The 3-5 um wavelength range is technologically important because it is used for applications including; remote gas sensing, range-finding and night vision, bio-medical imaging for diagnosis in healthcare and sensitive detection in optical spectroscopy. However, the development of instrumentation is limited by the availability of efficient, affordable light sources and photodetectors, which is directly determined by the semiconductor materials which are currently available. By introducing small amounts (~ 1%) of N into InAs(Sb) we have shown that it is possible to access the mid-infrared using a new (dilute nitride) semiconductor and we are now seeking to engineer its band structure in order to significantly enhance the material's optical properties and increase quantum efficiency for light detection and emission. To enable the development of new photodetectors we will exploit the sensitivity of the conduction band to the resonant interaction of the N-level with the extended states of the host InAsSb crystal lattice to tailor the photoresponse and create a near ideal situation for electron acceleration and avalanche multiplication, resulting in a much larger detectable signal. To minimise the unwanted processes causing excessive noise and dark current, which compete with the avalanche multiplication and light detection in the detector, we shall arrange for the avalanche multiplication to be initiated by only one carrier type (electrons in our case). Many applications rely on the detection of very weak signals consisting of only a few photons. Conventional photodiodes have a limited sensitivity, especially if high speed detection is needed. In applications which are "photon starved", avalanche photodiodes (APDs) can provide an effective solution. However, at present effective avalanche multiplication in the mid-infrared spectral range can only be obtained by using exotic CdHgTe (CMT) semiconductor alloys. The resulting detectors require cooling, thus making CMT-based APDs prohibitively expensive for all except military applications. Simpler fabrication, low noise, low operating voltage, inexpensive manufacturing and room temperature operation, together with monopolar electron ionisation are all significant advantages of APDs based on the dilute nitride materials compared to existing technologies. Similarly, we shall enable the development of more efficient mid-infrared light sources. By adjusting the N content within InAsN(Sb) quantum wells and carefully tailoring the residual strain and carrier confinement, we shall be able to defeat competing non-radiative recombination processes whilst simultaneously enhancing the light generation efficiency. These novel quantum wells would then form the basis of the active region from where the light is generated, either within an LED or a diode laser. Currently mid-infrared LED efficiency is low at room temperature, and with the improvements which we shall deliver; we envisage that devices with significantly higher dc output power will be developed following our lead. Mid-infrared diode lasers incorporating our strained dilute nitride quantum wells are also expected to exhibit a reduced threshold current and could offer an affordable alternative to existing technology, especially in the 3-4 um spectral range. We will produce prototype photodetectors and LEDs and use these to demonstrate the above-mentioned avalanche behaviour and quantum efficiency improvements respectively. We shall validate our dilute nitride materials and structures in close collaboration with our collaborators at NPL, SELEX, CST and INSTRO to evaluate performance for use in practical applications and help ensure uptake of our technology.

The assessment of human health from analysis of blood samples is one of the most widespread medical diagnostic procedures; with thousands of patients providing samples every day in hundreds of clinics and surgeries across the UK. However, it remains a slow process because samples have to be sent to a limited number of specialist central services in health trusts, with a turn-around of days between sample acquisition and assessment delivery. It is expensive, both in terms of direct cost of the analysis and downstream costs due to deterioration of patient health as a result of the time delay in accessing results. We propose a capillary driven, microscale disposable chip instrument for non-technical users that provides the established and understood diagnostic parameters. The basic device will consist of lasers and detectors integrated around a fluid channel to facilitate counting, scattering and wavelength dependent absorption measurements. This will differentiate red blood cells from white blood cells, discriminate between the main white blood cell types - monocyte, lymphocyte, neutrophil and granulocyte - and provide cell counts of these sub groups. Stage 2 builds on the same technology platform to enhance sensitivity and add functionality by making the cell under test an active part of the laser thus maximising light / cell interaction. In stage 3 we will label cells with fluorescent dye attached to metal particles (provided by Keyes group) and increase the absorption of particular cells, by up to 6 orders of magnitude, and also access fluorescent lifetime measurements (using an approach we have patented) allowing the analysis of cell function as well as cell discrimination. We have blood analysis expertise within the project to maximise the benefits of stage 1 and co-workers focussed on cell cycle and anti-cancer research will interact and maximise the benefits of the device that goes well beyond current blood test capability. The microscale system we will develop offers a number of advantages: Micro scaling reduces the volume of blood required changing the way blood-based diagnostics are used. Immediate and quasi-continuous monitoring of the haematological state is feasible and can be used in acute situations such as surgery or child birth. This also offers, with further development, a realistic route to continuous monitoring during everyday life. Semiconductor micro fabrication provides the route to mass manufacture of low cost systems. Shifts the cost of blood testing from technician to test kit and introduces a distributed cost model (pay per kit) rather than a single, major capital investment. Allows disposable chip format and provides uniformity and repeatability, contributing to the removal of the need for specialist operator - use at point of care, e.g. developing world. We will achieve all this by exploiting the properties of a quantum dot semiconductor system that we have developed and which provides particular advantages for integration and for laser based sensing at relevant wavelengths (a major one being the sensitivity to small changes in optical loss). In addition to the significant medical benefits resulting from the ability to widely deploy, low cost and enhanced clinical functionality devices we also see a significant commercial benefit to the UK, with an identified UK manufacturing supply chain. The project brings together a wide range of complementary experience, including semiconductor device design, fabrication and characterisation, microfluidics, systems analysis and data handling, blood analysis and cytometry and biophotonics and clinical validation.

Current applications for semiconductor lasers are wide ranging and pervade every aspect of life. Indeed, in the developed world, most people already own several lasers and gain the benefit of many more. With every new technology, this proliferation is set to continue. Most importantly, the laser enables the internet age since all data transmitted around the globe is carried as flashes of laser light. As a consequence most people in the developed world have come to depend on many lasers during a typical day. The reduction in their cost of ownership is therefore of critical importance to the extension of these benefits to the developing world and also bringing new benefits to us all. The potential future applications of photonics are seemingly unlimited, with new technologies and applications continuing to emerge. The key advantage of a semiconductor laser is that if an application has sufficiently large volume, the cost of the semiconductor laser is very low. The DVD player is a good example -with the laser costing a few pence each. The semiconductor laser therefore enables new technologies, devices and processes to be commercialized. However, semiconductor lasers must be able to generate the required "flavour" of light; i.e. the correct wavelength, spectral width, power, polarization, beam shape, etc. Some of the fundamental parameters of a semiconductor laser may be controlled by the design and choice of materials, e.g. wavelength, spectral purity (line-width). However, using current technologies the polarization and beam profile are generally fixed at manufacture and may only be subsequently altered by extrinsic optical components. This introduces additional cost (increasing the environmental impact) and reduces the overall efficiency and usefulness of the device. For future engineers and scientists it would be ideal if there were complete control of the output from a semiconductor laser, providing unlimited possibilities in terms of future applications. The alteration of matter on the scale of the wavelength of light is known to allow the control of the optical properties of a material. Even the laser in something as simple as a mouse incorporates a number of such technologies. We will develop novel nano-scale semiconductor fabrication to modify light-matter interaction and engineer the control of the polarization and form of a laser beam. Our work will realise a volume manufacturable photonic crystal surface emitting laser (PCSEL) for the first time. The nano-scale photonic crystal is responsible for controlling the properties of the laser. It is simply a periodic pattern similar in size to the light itself, a natural example of this periodic patterning produces the blue colour in some butterfly wings, or the iridescence of opal. In our case, every detail of the photonic crystal will be modeled, understood and optimized to control the properties of the laser to meet a range of needs. Lasers will be designed to exhibit almost zero divergence and will also allow, for the first time, the electronic control of divergence and polarization and allow the direct creation of custom engineered beam profiles and patterns. The realization of high efficiency, area scalable high power lasers with ideal beam profiles will contribute to reduced energy consumption in the manufacture of laser devices, and in their cost of ownership. The technologies developed will allow the ultimate in design control of future optical sources, hopefully limiting laser applications only to the imagination. Once successful, such devices will displace existing lasers in established commercial photonics and enable many more emerging application areas. This will be made possible by introducing both new functionality to laser devices and reducing the cost of existing products. We will develop this technology alongside physical understanding and device engineering, liaising closely with world-leaders in the volume manufacturer of such devices.