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This thesis presents a novel synthesis that generalizes the Doherty power amplifier theory of operation with regard to the combiner parameters. This analysis introduces, through a new parameter "x", simple formulae that re-define the relationships between the combiner parameters for a load modulation process over wide bandwidth and efficient usage at the combiner elements.

No description available.

No description available.

n-type transparent conducting oxides (TCOs) have been studied extensively and are now commercially available. The development of p-type counterparts lags someway behind, despite the opportunity preparing such materials offers. Interest in tin oxide (SnO2) thin films and their applications has grown significantly over recent years, particularly for the preparation of p-type TCOs. However for this to be realised, limitations such as the ionisation energy of acceptor defects and the existence of compensating mechanisms must be overcome. Even though the effectiveness of acceptor doping is essential, the presence of compensating defects as the film growth environment changes is critical for stable p-type TCOs. Here a growth study of SnO2 deposited using pulsed laser deposition (PLD) reveals intrinsic acceptor defects have limited contribution to the conductivity as theoretically predicted. The conductivity remains n-type despite significant variation in the oxygen content of the growth environment and temperature - which is attributed to the large concentration of tin interstitial defects. To limit donor defect concentration, elevated temperature and oxygen pressure were set as the growth conditions with the introduction of Zn as an acceptor dopant. Here, the introduction of Zn acceptors changes the behaviour of intrinsic defects such that measured charge carrier concentrations increase by some 3-orders of magnitude compared with undoped films, suggesting the presence of compensating mechanisms. n-type behaviour persists, even after oxygen annealing, and film resistivity also increases. This is attributed to the formation more acceptor defects that act as electron compensation centres. Zn is reported to act not only as an acceptor in SnO2 but also to enhance n-type conductivity: here this behaviour is also confirmed. By studying the electrical, optical and structural properties of Zn doped SnO2, films of surprisingly low resistivity (2.9 x 10-3 Ω.cm) were formed, which exhibited preferential (200) on Zn addition. An observed decrease in bandgap was found when Zn doping was increased, from 3.6 eV in undoped films down to 3.4 eV in crystalline films and 3.2 eV in amorphous films. The work is concluded by investigating low deposition temperature where low resistivity highly transparent films are formed at temperatures as low as 100 degree celcius.

High-level synthesis (HLS) promises a significant shortening of the digital hardware design cycle by raising the abstraction level of the design entry to high-level languages such as C/C++. However, applications using dynamic, pointer-based data structures remain difficult to implement well, yet such constructs are widely used in software. Automated optimisations that leverage the memory bandwidth of dedicated hardware implementations by distributing the application data over separate on-chip memories and parallelise the implementation are often ineffective in the presence of dynamic data structures, due to the lack of an automated analysis that disambiguates pointer-based memory accesses. This thesis takes a step towards closing this gap. We explore recent advances in separation logic, a rigorous mathematical framework that enables formal reasoning about the memory access of heap-manipulating programs. We develop a static analysis that automatically splits heap-allocated data structures into provably disjoint regions. Our algorithm focuses on dynamic data structures accessed in loops and is accompanied by automated source-to-source transformations which enable loop parallelisation and physical memory partitioning by off-the-shelf HLS tools. We then extend the scope of our technique to pointer-based memory-intensive implementations that require access to an off-chip memory. The extended HLS design aid generates parallel on-chip multi-cache architectures. It uses the disjointness property of memory accesses to support non-overlapping memory regions by private caches. It also identifies regions which are shared after parallelisation and which are supported by parallel caches with a coherency mechanism and synchronisation, resulting in automatically specialised memory systems. We show up to 15x acceleration from heap partitioning, parallelisation and the insertion of the custom cache system in demonstrably practical applications.

Textile and semiconductor processes were combined to produce a flexible solar panel by depositing silicon thin film onto woven polyester. Semiconductor processes such as evaporation, Plasma Enhanced Chemical Vapour Deposition (PECVD) and RFsputtering were done under vacuum conditions. Microwave PECVD proved difficult for textile substrates as the weave was damaged using parameter settings commonly used for conventional substrates such as silicon wafers and glass. PECVD parameters such as temperature, gas flow-rate, mixture, pressure and power were adjusted to allow the textile to be processed and a good quality silicon thin film to be deposited. An extra conductive layer was introduced between the textile and metal back-contact to support the cell. The silicon film structure changed from amorphous to mixed crystal growth in an amorphous matrix, as revealed by Raman spectroscopy and light transmission. The silicon Raman spectrum often had three peaks with the middle one, a fingerprint for nanocrystal growth with a hexagonal wurtzite structure in between the amorphous and crystalline peaks. Process conditions for pure amorphous and microcrystalline structures were also established, requiring two peaks to fit the Raman spectrum. Different structures have different band-gap energies and these were determined by measuring the variation in light transmission. An amorphous structure has a band-gap energy of 1.8eV while a crystalline silicon structure has a band-gap of 1eV and a mixed nanocrystalline content has an intermediate value which depends on the crystal size. A microcrystalline structure has a band-gap of 1.6eV.

The mercury-drop electrode technique, when used to measure the current/voltage characteristics of thin films of molecular rectifiers, is a useful, if awed method of analysis. Current/voltage plots taken from a number of samples confirm previous studies taken using the scanning tunnelling microscope (STM), but indicate significant levels of penetration of the mercury into the sample or stabilising monolayer. Quartz crystal microbalance (QCM) studies of the adsorption of 7,7,8,8°- tetracyanoquinodimethane (TCNQ) onto clean gold indicate small but significant adsorption, with possible formation of a salt, via conversion of TCNQ into the radical anion. This has implications for the results of previous experiments, which indicate alternative sources for the rectification observed from donor-bridge-acceptor systems, but also suggest use of the TCNQ radical anion as a electron donor when used to replace the counterion present in a number of self-assembled systems. Previous STM- based measurements confirming this latter suggestion are supported by mercury-drop studies. The results support conclusions previously drawn by a number of authors, removing much of the ambiguity surrounding their interpretation, whilst clarifying the adsorption characteristics of thiol-based molecules that contain a terminal TCNQ group, and to some extent, TCNQ itself. It is suggested that the mercury-drop technique should never be used in isolation to quantify rectification in monolayers of molecular rectifiers, but that it is suitable for use only i confirming and checking results from more established procedures.

This thesis comprises works on novel quantum dot structures. New ways of growing III-V semiconductor quantum dots by integrating a ternary element or by growing on top of a silicon wafer are optically characterized, opening the way to more specific work on those new structures, while furthering our understanding of the epitaxy mechanisms behind them. We study InGaAs/GaAs quantum dot structures monolithically grown on a silicon substrate, without use of germanium virtual substrate nor wafer bonding technique. Optical characterization of the sample with micro photoluminescence is performed and shows very good single quantum dot emission lines. Single photon emission from the InGaAs dots is demonstrated with photon correlation experiment showing clear anti-bunching. Photonic crystal cavities are fabricated for the first time with InGaAs dots monolithically grown on silicon and exhibit very high quality factor up to 13000 with a large percentage of cavities having Q-factors over 9000. This allows observation of Purcell effect for single photon emitting QDs and strong light-matter coupling between InGaAs QDs and cavities. We also investigate unexpected emission lines on the same sample. The lines are identified as interface fluctuations in a GaAs/AlGaAs short period superlattice, making them the first Interface fluctuation quantum dots grown directly on silicon. Further optical characterization confirms the quantum dot nature of the emissions. Polarization measurements allow study of the fine structure splitting of exciton/bi-exciton pairs and the single photon emission of the dots is demonstrated. Finally in a subsequent chapter we investigate InP/GaInP quantum dots with arsenic deposited during the growth process. Magneto-optic PL of samples with different concentrations of As allows to determine how the As changes the characteristics of the dots. Schottky diodes are fabricated and tested to show good characteristics, and electric field experiments demonstrate charge control over this new kind of dots.

This thesis describes the optical spectroscopic measurements of III-V semiconductors used to investigate a number of issues related to the development of integrated quantum optical circuits. The disorder-limited propagation of photons in photonic crystal waveguides in the slow-light regime is investigated. The analysis of Fabry-Perot resonances is used to map the mode dispersion and extract the photon localisation length. Andersonlocalised modes are observed at high group indices, when the localisation lengths are shorter than the waveguide lengths, consistent with the Fabry-Perot analysis. A spin-photon interface based on two orthogonal waveguides is introduced, where the polarisation emitted by a quantum dot is mapped to a path-encoded photon. Operation is demonstrated by deducing the spin using the interference of in-plane photons. A second device directly maps right and left circular polarisations to anti-parallel waveguides, surprising for a non-chiral structure but consistent with an off-centre dot. Two dimensional photonic crystal cavities in GaInP and full control over the spontaneous emission rate of InP quantum dots is demonstrated by spectrally tuning the exciton emission energy into resonance with the fundamental cavity mode. Fourier transform spectroscopy is used to investigate the short coherence times of InP quantum dots in GaInP photonic crystal cavities. Additional technological developments are also presented including a quantum dot registration technique, electrical tuning of quantum dot emission and uniaxial strain tuning of H1 cavity modes.