16 cm-2) of cadmium and telluriumcan be implanted without forming amorphous lattice disorder by heating the gallium arsenide during implantation to relatively low temperatures (~ 200°C) at which no appreciable dissociation of the gallium arsenide or broadening of the implanted profiles by diffusion occurs. Atom site location measurements have shown that a large fraction of a tellurium dose implanted at 180°C is located on or near lattice sites but that in the case of cadmium the fraction depends on the implanted dose. Channelled backscatter measurements have shown that there is residual disorder or lattice strain in gallium arsenide implanted at elevated temperatures. The extent of this disorder has been shown to depend on the implanted dose and implantation temperature. The channeling effect has been used to measure annealing of the disorder. It has been concluded from this work that for high dose implantations of cadmium and tellurium, it is more advantageous to implant at 180°C than at room temperature. To achieve efficient doping, however, it could be necessary to anneal the residual lattice disorder. Pyrolitieally deposited silicon dioxide is not a suitable encapsulation for this purpose.

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At this work the principle aim is to create new low cost hardware test circuitry that can emulate the behavior of solar cells under different insolation and temperature conditions. Another goal is to propose a new MPPT algorithm that could accurate and reliable estimate the maximum power operating point. The transcendental equation describing a solar cell IV characteristic contains current on both sides in a function of the form I = f (V, I). In this work, a current-independent voltage expression is derived for the maximum power point as a function of a new variable which is mathematically well defined. Validation is performed on four different photovoltaic modules. The best case scenario has shown a divergence in Pmpp of 0.08% while the worst 0.84%. The new method is examined for sensitivity, up to %5± on values of five fitting parameters (Rs, Rsh, n, Io, Iph), with Iph to have the higher impact effect (up to 5% error). Two topologies, of VBE multiplier, have been proposed that can reliably emulate solar cell operation. Analysis shows that both circuits have the potential to deliver good quality characteristic IV curves with small RMSE (10-3). The second improved VBE multiplier has the ability to operate over wider range of illumination and temperature conditions. Through this model it was possible to build a low cost (£230) fully functional prototype digital controlled emulator solar system “DiceSol”. A MPPT device has implemented based on a powerful mathematical modeling tool. The proposed method “Goose Waddle (GW)” was employed on a boost DC/DC converter configuration. Excellent static and dynamic performances were exhibited. At all cases considered convergence is higher than 98.53% while convergence time is on average 220 msec.

Finite Elements Method simulations of Total Ionizing Dose in two state-of-the-art transistor nodes are presented: The 45 nm Partially-Depleted Silicon-on-Insulator MOSFET and the 22 nm bulk FinFET. A systematic method has been developed to study charge trapping in field isolation oxides using the simulation software Sentaurus device. The method is based on solving transport equations for carriers in the oxide. Aspects of simulation of interface trap formation through de-passivation from ionic hydrogen are discussed. This includes transport of hydrogen species in the device and state transitions. Calibration of the trapping model is performed using experimental results on Buried OXide irradiated capacitors of 400 nm SiO2. The extracted parameters are then used in the two FET technologies examined. In both cases, increased radiation hardness of the devices, tested using the bulk traps method, up to total doses of 600 KRad(SiO2) in the case of the PDSOI and 1 MRad(SiO2) in the case of the FinFET is shown. In the 45nm node, Random Dopant Fluctuations (RDFs) using the Sano and the Impedance Field Method are examined in combination with charge introduced in the field oxide regions. RDFs are shown to have a significant effect in the sub-threshold characteristics of the irradiated devices during the weak inversion of the parasitic transistor induced in the device. Their effect is negligible, however, when the parasitic channel is fully formed.

This thesis describes new characterization techniques that can be used to investigate nematic liquid crystal (LC) materials and systems, and experimental studies of new hybrid LC devices. The characterization techniques include an all-optical method for determining nematic viscosities, a multi-spectrum analysis (VTF) of the electro-optic response of an LC device subject to an AC field, and a measurement of two-beam coupling (TBC) in photorefractive LC systems subject to an AC field. The time response measurement is the first experimental study of fast director oscillations seen when a modulated field is applied to a cell, and it has been shown that Erickson-Leslie theory can be used to determine the rotational viscosity by fitting to these oscillations. The VTF has been used to show that the conductivity of the LC E7 is 2 x that of TL205, and can explain the origin of higher beam coupling in E7 photorefractive devices. The AC driven TBC and its analysis has proved that a non-ohmic photoconductor will lead to two distinct beam coupling regimes in frequency space, and has shown that optimum beam coupling efficiency can be obtained by tuning the AC frequency. The range of new hybrid LC devices investigated here include cells using an LC doped with multiferroic nanoparticles, and photorefractive cells that use a new electrode material (PEDOT) to reduce injection barriers in standard photorefractive devices, a photorefractive polymer (JTDA16) as an aligning layer, and a photoaligning layer (PAAD) to enhance the modulation depth of induced photorefractive gratings. The multiferroic nanoparticle study showed that a magneto-optic response could be observed at low fields (< 500 Gauss), and that the sol-gel process for growing nanoparticles is not appropriate for creating ferroelectric layers with thicknesses below ~ 15 nm. The new materials for photorefractive cells have shown promising results, with observed diffraction efficiencies up to 13 x higher than a benchmark cell using polyvinyl carbazole as a photoconductor.

The motivation behind this research is to bring cheap, low-cost and clean energy technologies to the society. Colossal use of fossil fuel has created noticeable pollution problems contributing to climate change and health hazards. Silicon based solar cells have dominated the market but it is cost is high due to the manufacturing process. Therefore, the way forward is to develop thin films solar cells using low-cost attractive materials, grown by cheaper, scalable and manufacturable techniques. The aim and objectives of this work is to develop low-cost, high efficiency solar cell using electrodeposition (ED) technique. The material layers include CdS and ZnTe as the window materials, while the absorber material is CdTe. Fabricating a suitable devices for solar energy conversion (i.e. glass/conducting glass/window material/absorber material/metal) structure. Traditional way of fabricating this structure is to grow window material (CdS) using chemical bath deposition (CBD) and absorber material (CdTe) using electrodeposition. However, CBD is a batch process and therefore creates large volumes of Cd-containing waste solutions each time adding high cost in manufacturing process. This research programme is therefore on development of an "All ED-solar cells" structure. Material studies were carried out using photoelectrochemical (PEC) studies, UV-Vis spectrophotometry, X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Furthermore, the electrical characterisation of fully fabricated devices was performed using current-voltage (I-V) and capacitance-voltage (C-V) measurements. This research programme has demonstrated that CdS and ZnTe window materials can be electrodeposited and used in thin film solar cell devices. The CdS electrolytic bath can be used for a period of 7 months without discarding it like in the CBD process which usually has life-time of 2-3 days. Further work should be carried out to increase the life-time of this bath, so that there can be used continuously minimising waste solution production in a manufacturing line. An efficiencies showing up to 7% was achieved for complete devices. However, the consistency and reproducibility remains un-resolved due to production of efficiencies between (2 - 7)% efficient devices varying from batch to batch. One of the reasons has been identified as the growth of CdS nano-rods with spacing between them. This is the first observation of CdS nano-rods and could open up many applications in nano-devices area. In order to improve the consistency of the solar cell efficiency, CdS layers should be grown with nano-rods aligned perpendicular to the glass surface and with tight packing without gaps, or with uniform coverage of CdS over the conducting glass surface. The possibility of growth of CdTe absorber layers with n- and p-type electrical conduction using change of stoichiometry was confirmed using the results presented in this thesis. This is a key finding, important to form multi-layer solar cell structures in the future.

The thin film transistor (TFT) is one of the most important fundamental building blocks in modern electronic devices. Examples of TFT applications are in integrated circuits (ICs), amplifiers, addressing of flat panel displays, and also as chemical sensors, e.g. as ion- selective field effect transistors (ISFETs). Although the most common semiconductor materials used in thin film transistors (TFTs) is silicon (Si), the versatility of TFTs allows other semiconductors to be used instead of Si-based materials. Recent research effort has been directed towards alternative TFT semiconductors, for example solution-processable semiconductors that enable new manufacturing options. Since the 1990s, soluble semiconducting polymers have been intensely researched for TFT applications. The possibility to engineer their transport (HOMO/LUMO) levels via chemical synthesis, their low temperature processing from solution, and their mechanical flexibility offers the potential for economical device production, as well as large-area and flexible applications. In the last view years, the interest as promising materials for the next generation of TFTs has shifted towards oxide based semiconductors such as ZnO due to their high performance and relative stability to ambient conditions. The potential of ZnO was boosted by the discovery that it can derived by pyrolysis of an organic precursor that is soluble in polar organic solvents (e.g. alcohols, ketones) thus enabling solution processing of ZnO TFTs and other devices. In addition, it has been demonstrated that both organic thin films and ZnO films can be gated by a field effect with very low threshold using deionized (DI) water as an electrolytic gate medium, leading to the ‘water- gated thin film transistors’ (WGTFTs). This discovery marks the beginning of a new method for the sensing of waterborne analytes, which differs from the classic ISFET in one significant point: Here, the aqueous sample under test is an active portion of the transducer. A number of works have since been undertaken using this discovery as a novel sensor concept for detecting waterborne analytes. Such sensors rely in the integration of analyte- specific sensitisers into the TFT architecture. For the selective sensing of ions, one of the most prominent families of water- insoluble ion sensitisers (‘ionophores’) are the calixarenes, a family of organic macrocycles. Calixarenes can be designed to selectively to complex specific cations, anions and neutral molecules.

Development of light-emitting diode technology is driven mainly by the need for efficient solid-state lighting, but it is also creating opportunities for new applications such as visible light communications (VLC). Here, the solid-state visible light sources are used to transmit data with the added requirement of a short excited-state lifetime so that sources can be modulated at high speed. This research focuses on hybrid optical sources for visible light communications with an emphasis on novel formats of colour-converters for multi-wavelength photoluminescence as well as white-light generation. Such converters include red and green colloidal quantum dots, the organic semiconductor BBEHPV andII-VI / III-V epitaxial structures. Solution-processable and environmentally stable polymeric films based on red and green colloidal quantum dots are demonstrated. Modulation bandwidth up to 24 MHz, photoluminescence quantum yields up to 61% and peak emission tunability across the visible spectrum makes these materials interesting as colour-converters for VLC. Free-space data transmission was demonstrated in this case with data rates up to 400 Mbit/s and 500 Mbit/s using 2-PAM modulation scheme for green and red quantum dots, respectively. Hybrid sources consisting of 450nm InGaN LEDs with capillary-bonded micron-thick ZnCdSe/ZnCdMgSe multi-quantum-well colour-converting membranes with peak emission at 540 nm are reported. After processing, the membrane was capillary bonded onto the sapphire side of the μLED resulting in a maximum converted average power of 37 μW. The -3dB optical modulation bandwidth of the bare LED, hybrid device and II-VI were 79 MHz, 51 MHz and 145 MHz, respectively. Visible light communication using both InGaN LEDs and a InGaN laser diode, down-converted by a red-emitting AlInGaP multi-quantum-well nanomembrane are also reported. Similarly to the previous devices, the AlInGaP nanomembrane was bonded onto the μLED array. For the down-converted laser diode approach, the nanomembrane can be sandwiched between a sapphire lens and optionally onto a distributed feedback reflector. The down-converter structure is remotely excited by the laser diode. Data transmission up to 870 Mb/s using M-PAM andOFDM modulation schemes is demonstrated for the μLED integrated nanomembrane. ODFM transmission at 1.2Gb/s is achieved for the laser diode pumped sample.

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