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In this paper, we present a systematic study of the effect of growth parameters on the structural and optical properties of InAs quantum dot (QD) grown under Stranski-Krastanov mode by molecular beam epitaxy. The dot density is significantly reduced from 1.9E10 to 0.6E10 cm-2 as the growth rate decreases from 0.075 to 0.019 ML/s, while the island size becomes larger. Correspondingly, the emission wavelength shifts to the longer side. By increasing the indium fraction in the InGaAs capping layer, the emission wavelength increases further. At indium fraction of 0.3, a ground state transition wavelength as long as 1.4 microns with the excited state transition wavelength of around 1.3 microns has been achieved in our dots. The optical properties of QDs with a ground state transition wavelength of 1.3 microns but with different growth techniques were compared. The QDs grown with higher rate and embedded by InGaAs have a higher intensity saturation level from excitation dependent photoluminescence measurements and a smaller intensity decrease from temperature dependent measurements. Finally, single mirror light emitting diodes with a QD embedded in InGaAs have been fabricated. The quantum efficiency at room temperature is 1.3%, corresponding to a radiative efficiency of 21.5%.

This thesis considers the current state of technology in three areas of novel protein production, namely: single cell protein, leaf protein and novel oilseed crops, with particular reference to oilseed rape. These three topics are chosen for study because of the potential contribution which they could make to UK food supply, and it is the quality and quantity of that contribution which is explored in this work. The assessment of the technologies is aci1ieved by a broadly based and thorough literature review to enable likely future developments to be made clear. A forecasting study is used to assess future prospects for oilseed crops such as· oilseed rape, lupin, sunflower and linseed in the United Kingdom. Energy and economic analyses are used to develop a comparative picture of the three novel processes. Finally, a model predicting the protein and energy supply of UK agriculture based on a vegan system is considered and the novel technologies are applied to it. Similarly, vegetarian and conventional systems are reviewed and the contribution of oilseeds, single cell protein and leaf protein are included in those systems. Little advantage is revealed by the use of the novel proteins in a vegan system of agriculture. When animal production is included in the model a contribution from novel proteins is seen to be of value. However, taken in turn, single cell protein is seen to have a limited future owing to its high energy and capital requirements, and the success of leaf protein is still limited by necessary further technical and process innovation. Agriculturally produced proteins are the cheapest and most acceptable in the UK, with home-grown oilseed rape providing an increasing proportion of our requirements.

The use of photonic crystals (PCs) for realistic light emitting diodes (LEDs) is discussed, given the constraints of planar semiconductor technology. A viable route for the fabrication of high-efficiency high-brightness electrically injected LEDs is presented. The starting point is a top-emitting microcavity using a single Alox Bragg mirror. The active area is surrounded by two-dimensional PCs, namely arrays of air rods etched through the top layers; injection of the electrons is achieved through the crystals. Design rules for PCs as efficient out-couplers are detailed. The building blocks are assessed experimentally, and we show that promising results are at hand.