No description available.

Thesis (M.S. in Physics)--Naval Postgraduate School, Sept. 2004. / Thesis advisor(s): Nancy M. Haegel. Includes bibliographical references (p. 45). Also available online.

Thesis (Ph. D.)--University of Hong Kong, 1998. / Includes bibliographical references (leaves 186-187).

Thesis (Ph. D.)--Drexel University, 2006. / Includes abstract and vita. Includes bibliographical references (leaves 157-168).

Thesis (Ph. D.)--Drexel University, 2006. / Includes abstract and vita. Includes bibliographical references (leaves 175-185).

Thesis (Ph. D.)--University of Hong Kong, 2007. / Also available online.

abstract: The long wavelength infrared region (LWIR) and mid wavelength infrared region (MWIR) are of great interest as detection in this region offers a wide range of real time applications. Optoelectronic devices operating in the LWIR and MWIR region offer potential applications such as; optical gas sensing, free-space optical communications, infrared counter-measures, biomedical and thermal imaging etc. HgCdTe is a prominent narrow bandgap material that operates in the LWIR region. The focus of this research work is to simulate and analyze the characteristics of a Hg1-xCdxTe photodetector. To achieve this, the tool `OPTODET' has been developed, where various device parameters can be varied and the resultant output can be analyzed. By the study of output characteristics in response to various changes in device parameters will allow users to understand the considerations that must be made in order to reach the optimum working point of an infrared detector. The tool which has been developed is a 1-D drift diffusion based simulator which solves the 1-D Poisson equation to determine potentials and utilizes the results of the 1-D electron and hole continuity equations to determine current. Parameters such as absorption co-efficient, quantum efficiency, dark current, noise, Transit time and detectivity can be simulated. All major recombination mechanisms such as SRH, Radiative and Auger recombination have been considered. Effects of band to band tunnelling have also been considered to correctly model the dark current characteristics. / Dissertation/Thesis / M.S. Electrical Engineering 2011

In the last few years research has identified Photonic Crystals (PhCs) as promising material that exhibits strong capability of controlling light propagation in a manner not previously possible with conventional optical devices. PhCs, otherwise known as Photonic Bandgap (PBG) material, have one or more frequency bands in which no electromagnetic wave is allowed to propagate inside the PhC. Creating defects into such a periodic structure makes it possible to manipulate the flow of selected light waves within the PhC devices outperforming conventional optical devices. As the fabrication of PhC devices needs a high degree of precision, we have to rely on accurate numerical modelling to characterise these devices. There are several numerical modelling techniques proposed in literature for the purpose of simulating optical devices. Such techniques include the Finite Difference Time Domain (FDTD), the Finite Volume Time Domain (FVTD), and the Multi-Resolution Time Domain (MRTD), and the Finite Element (FE) method among many others. Such numerical techniques vary in their advantages, disadvantages, and trade-offs. Generally, with lower complexity comes lower accuracy, while higher accuracy demands more complexity and resources. The Complex Envelope Alternating Direction Implicit Finite Difference Time Domain (CE-ADI-FDTD) method was further developed and used throughout this thesis as the main numerical modelling technique. The truncating layers used to surround the computational domain were Uniaxial Perfectly Matched Layers (UPML). This thesis also presents a new and robust kind of the UPML by presenting an accurate physical model of discretisation error. iv This thesis has focused on enhancing and developing the performance of PhC devices in order to improve their output. An improved and new design of PhC based Multiplexer/Demultiplexer (MUX/DEMUX) devices is presented. This is achieved using careful geometrical design of microcavities with respect to the coupling length of the propagating wave. The nature of the design means that a microcavity embedded between two waveguides selects a particular wavelength to couple from one waveguide into the adjacent waveguide showing high selectivity. Also, the Terahertz (THz) frequency gap, which suffers from a lack of switching devices, has been thoroughly investigated for the purpose of designing and simulating potential PhC based switching devices that operate in the THz region. The THz PhC based switching devices presented in this thesis are newly designed to function according to the variation of the resonant frequency of a ring resonator embedded between two parallel waveguides. The holes of the structures are filled with polyaniline electrorheological fluids that cause the refractive index of the holes to vary with applied external electric field. Significant improvements on the power efficiency and wavelength directionality have been achieved by introducing defects into the system.

New technologies will require more and more compliant materials capable of conforming to curved surfaces, i.e., able to stretch and mechanically resist body motions for wearable and on-skin applications. In this regard, this work discusses strategies to induce stretchability in materials. We focused our attention on improving the elasticity of transparent conducting electrodes (TCE) based on PEDOT:PSS and semiconductors (active layer) for organic solar cells. Firstly, the introduction of DMSO and Zonyl as additives into PEDOT:PSS was shown to produce highly transparent conducting electrodes (FoM > 35) with low Young’s modulus and high carrier density. We investigated the relationship between the transport properties of PEDOT:PSS and the morphology and microstructure of its films. The combination of the two additives enhances the fibrillary nature and the aggregations of both PEDOT and PSS components of the films. Secondly, stretchable TCEs based on PEDOT:PSS were fabricated using an innovative approach that combines an interpenetrated polymer network-based on polyethylene oxide and Zonyl. The presence of three-dimensional matrix provided high electrical conductivity, elasticity, and mechanical recoverability. The potential of this electrode was demonstrated with indium-tin-oxide (ITO)-free solar cells with a power conversion efficiency similar to ITO. Finally, the research was completed by integrating a cross-linker or an elastomer into the active layer to enhance its stretchability while maintaining excellent photovoltaic performance. In particular, SEBS elastomer exhibited a tailored elasticity with various fullerene and non-fullerene blends: P3HT:PC61BM, PCE10:PC71BM and PCE13:IT-4F. This versatile approach highlights the ease of manufacturing and scalability achieved by the solution casting processes along with a high compatibility of acceptor and donor blends.

Wide and direct bandgap semiconductors (WBSs) are promising materials for many deep UV (DUV) applications. However, several challenges presently hinder the enhancement of DUV optoelectronics, such as low crystal quality, as well as complex and costly fabrication and growth processes that prevent production of high-performance devices, especially for large-scale applications. As a part of the study reported in this dissertation, I demonstrate several novel WBS-based devices with improved or novel functionalities, for the first time. The first part of work reported in this dissertation is designated for the novel, highly ordered and well-defined hexagonal ZnO nanotube (NT) arrays that were obtained without a catalyst. These arrays were grown on a p-GaN template using pulsed laser deposition (PLD), resulting in a highly bright and cost-effective UV light emitting diode (LED). In the second part, Gd-doped ZnO NRs grown on cost-effective metal substrate by PLD are presented and it is demonstrated that these can be functionalized by CH3NH3PbI3 perovskite to extend the functionality of ZnO photodetector from the ultraviolet to the infrared region (λ > 1000 nm), for the first time. The work reported in the third part demonstrates that the PLD method adopted in the present study can be extended to other high-quality metal oxide nanostructures. For this purpose, uniform p-type CuO pyramids were grown by PLD on Si substrate without a metal catalyst. Moreover, laser ablation method was advanced from vacuum based (PLD) to liquid based (femtosecond-laser ablation in liquid − FLAL) method to synthesize high-quality ZnO quantum dots (QDs). Adoption of this novel strategy allows producing high-performance self-powered DUV photodetectors based on p-CuO pyramids/n-ZnO QDs heterojunction device. In the last part, this research field is further advanced by exploring the functionality of other metal oxides synthesized by FLAL to fabricate a high-performance self-powered DUV photodetector. Such photodetector was fabricated using p-MnO QDs that were synthesized by FLAL and functionalized by high-quality mechanically exfoliated n-β-Ga2O3 nanoflakes as an active heterojunction layer grown on SiO2, confirming its superior response. All fabrication strategies, including use of heterojunction structures (mainly p−n junction), adopted in this work overcome the aforementioned issues related to the currently available WBS devices.