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In this project we will combine the CMOS imager design skills at Oxford University and the thin-film technology of Sharp Laboratories Europe with the nanofabrication and nano-optics expertise at Glasgow University to, for the first time, implement plasmon enhanced technologies for use in imaging and displays. The proposed technology can provide both wavelength and polarisation control in a single fabricated layer on the surface of otherwise standard technologies. This is a major step-forward from present day technologies that rely on multiple layers of processing to achieve less powerful effects.Optical resonances occur at the surface of metal films due to the dielectric dispersion relation. This phenomenon leads to surface plasmon resonances (SPR). Surface plasmons are non-radiative electromagnetic surface waves that cause fluctuations in the surface electron density. The simplest exploitation of this phenomenon is in thin films where the dispersion relation is close to resonance, leading to the enhancement of the electric field of a propagating light wave. Surface inhomogeneity, such as a deliberately-created periodic undulation on the metal surface, is used to improve the coupling of the light to the plasmons [1] hence increasing the enhancement. More recent work has shown how nanoparticle structures made by techniques ranging from colloidal suspensions to direct-write lithography can lead to further SPR enhancement in small structures.CMOS integrated circuits are now the dominant technology for optical imaging, including digital cameras, microscopes and a range of optical instruments. Similarly, active display technologies have become dominant, and widespread, in industrial and commercial sectors. These electronic devices combine high performance with low cost and also enable designers to implement signal processing functions on to the same substrate as the imaging sensor to reduce cost, pixel size and power consumption. However, current technologies suffer from a number of drawbacks that are limiting progress in traditional markets. Furthermore, little is being done to enable the core technology to expand its functionality, and hence use, in new and emerging markets. The aim of this project is to use the emerging field of plasmonics to study the potential for using back-end-of-line (BEOL) processing at the silicon foundry to enable both enhancement and diversification of the capabilities of electronic optical detectors, imagers and displays.

This project will study the growth and characterisation of a new optoelectronic semiconductor material, namely indium nitride (InN). Starting from the deposition of the first few atoms that make up a single atomic layer of the material, the growth will be observed using scanning tunnelling microscopy (STM), through to the development of complete monolayers, and all the way to the growth of thin films (i.e. several microns thick). This material is important technologically because up until late 2002, it was thought that InN had a band-gap energy of 1.9 eV. However, in 2002, high quality InN thin films were grown for the first time and this material was found to have a band-gap energy of 0.7 eV (i.e. in the infra-red). This discovery has meant that it is important to re-assess all of the fundamental properties (i.e. structural, optical and electronic properties) of this material and its alloys. The technologically important reason for this is that now, with this lower band-gap energy, InN can be combined with the wide-gap material GaN (band gap of 3.4 eV / i.e. in the ultra-violet) to form InGaN. It will therefore be possible to make a whole range of new devices, including a range of high efficiency solar cells spanning the entire solar spectrum, and high frequency devices that operate in the THz band, without having to combine several different semiconductor materials, with all the problems that go with that complex process. Because of a range of inherent properties associated with pure InN (surface electron accumulation and difficulty with p-type doping) which we have previously discovered, we will develop a range of novel alloys of this material with both gallium (Ga) and arsenic (As). We will do this by carefully examining how these materials grow (quite literally atomic layer-by-atomic layer) and what fundamental properties of the thin films improve, as a function of Ga and As content, enabling a whole range of new optical and electronic device applications.

This project will study the growth and characterisation of a new optoelectronic semiconductor material, namely indium nitride (InN). Starting from the deposition of the first few atoms that make up a single atomic layer of the material, the growth will be observed using scanning tunnelling microscopy (STM), through to the development of complete monolayers, and all the way to the growth of thin films (i.e. several microns thick). This material is important technologically because up until late 2002, it was thought that InN had a band-gap energy of 1.9 eV. However, in 2002, high quality InN thin films were grown for the first time and this material was found to have a band-gap energy of 0.7 eV (i.e. in the infra-red). This discovery has meant that it is important to re-assess all of the fundamental properties (i.e. structural, optical and electronic properties) of this material and its alloys. The technologically important reason for this is that now, with this lower band-gap energy, InN can be combined with the wide-gap material GaN (band gap of 3.4 eV / i.e. in the ultra-violet) to form InGaN. It will therefore be possible to make a whole range of new devices, including a range of high efficiency solar cells spanning the entire solar spectrum, and high frequency devices that operate in the THz band, without having to combine several different semiconductor materials, with all the problems that go with that complex process. Because of a range of inherent properties associated with pure InN (surface electron accumulation and difficulty with p-type doping) which we have previously discovered, we will develop a range of novel alloys of this material with both gallium (Ga) and arsenic (As). We will do this by carefully examining how these materials grow (quite literally atomic layer-by-atomic layer) and what fundamental properties of the thin films improve, as a function of Ga and As content, enabling a whole range of new optical and electronic device applications.

Solar panel prices are plummeting and they are becoming more widespread, but the impact they can actually make to the carbon problem is ultimately limited by their efficiency. Even if the panels could be made for almost nothing, and if we all covered our roofs with them, at their present working efficiency they could only generate a small fraction of the year-round electricity we have become used to using. This project aims to develop a radically new way of harvesting solar power that has the potential to improve this conversion efficiency by a factor of 5, and so to put solar power in a position to make a major contribution to the carbon mitigation issue. The science behind our approach stems from the fact that behind the familiar beauty of the Rainbow lies a vexing problem if you want to the power of sunlight. Solar cells work by absorbing quanta of light, so-called photons, in a way that makes the electrons inside them jump from one energy level to a higher one, like a rung in a ladder. It's these electron jumps that capture the sunlight's energy The problem with sunlight is that each colour in the rainbow is made from different energy photons. No matter what rung height you decide on, some of the lower energy photons (at the red end of the rainbow) are lost because they can't power the jump. Others (at the blue end) have more energy than the rung spacing, so only part of their energy gets captured. A detailed analysis shows that, no matter what rung size you settle on, the best, the very best you can ever do is the so-called "Shockley-Queisser" efficiency limit, of 31%, and most actual solar cells struggle to reach half of this. Our research programme sets out to smash this "Shockley-Queisser" limit. We plan to do this by using quantum mechanics to design an energy level structure into the solar cell which is analogous to a ladder with a range of uneven rung spacings. Each rung grabs a different part of the rainbow with high efficiency, and some are designed so that one photon can make an electron jump up two rungs at a time. To do this we use a revolutionary approach that exploits the sort of nano-technology that gave us the lasers that power computer printers, the internet and DVD drives. Theory indicates that efficiencies up to 89% are possible. We hope and believe that demonstrating even part of this improvement will permanently change the way we design solar cells and dramatically improve the chances of solar power being adapted on a scale that is wide enough to have a genuine positive environmental impact. This cell also develops much more voltage than present designs, which makes its electrical output easier to use. As well as determining the rung spacing, we also use the nano-technology to add an extra , and critical twist, a new idea we are calling a "Quantum Ratchet". This can be thought of as, say, a small hollow in each rung, so that if an electron makes it up that far, the likelihood is that it will stay there long enough to absorb another photon and hop up to the next rung, rather than losing its captured energy by sliding back down. At the moment we are proposing to get as far as demonstrating and optimising the concept, using comparatively expensive test cells and complex laser spectroscopy in a University lab. Even that is a major undertaking though. It will occupy a focussed team of ~ 9 scientists for 4 years, all working towards the same goal if we are to have even a chance of success, but we all believe the results will be worth it.