Periodic dielectric structures, which are called photonic crystals or photonic lattices, have attracted many interests in recent years. The existence of band gaps, which prohibits the propagation of electromagnetic waves in any direction, provides an opportunity to confine and control the propagation of electromagnetic waves. This study aims at the influence of photonic band gaps which are brought by the errors because of the procedures of manufacturing. It is simulated that the crystal structures of 2-D square, triangular and honeycomb lattice, and the dielectric rods of circular and square whose size and form are little different from original design system. Consequently, it is found that the band gaps of 2-D photonic square lattice composed of cylinders, and triangular lattice composed of cylinders or square rods are different from original design system.

Photonic crystals (PC) are periodic structures that dictate the behavior of electromagnetic radiation and can be one-dimensional, two-dimensional or three-dimensional (3D). A 3DPC was modeled and fabricated based on a three-layer design resulting in a face centered cubic structure. Different simulation methods were used to show the existence of a complete 3D bandgap, and were verified experimentally by obtaining transmission measurements in several directions. A prototype of the structure was fabricated using ECCOSTOCK HiK high dielectric sheets (dielectric of 12) and machined using a computer and numerical controlled mill. Experiments to test this structure were performed in an anechoic chamber making use of a network analyzer, a pair of horn antennas, collimating lenses, and a track for alignment. Free-space Thru-Reflect-Line measurements were taken between 10GHz and 15GHz to obtain the transmission through the prototype. Finally, a defect layer was added to the structure at different locations and localized modes observed.

Photonic crystals (PC) are periodic structures that dictate the behavior of electromagnetic radiation and can be one-dimensional, two-dimensional or three-dimensional (3D). A 3DPC was modeled and fabricated based on a three-layer design resulting in a face centered cubic structure. Different simulation methods were used to show the existence of a complete 3D bandgap, and were verified experimentally by obtaining transmission measurements in several directions. A prototype of the structure was fabricated using ECCOSTOCK HiK high dielectric sheets (dielectric of 12) and machined using a computer and numerical controlled mill. Experiments to test this structure were performed in an anechoic chamber making use of a network analyzer, a pair of horn antennas, collimating lenses, and a track for alignment. Free-space Thru-Reflect-Line measurements were taken between 10GHz and 15GHz to obtain the transmission through the prototype. Finally, a defect layer was added to the structure at different locations and localized modes observed.

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<p>An important part in the design of analog integrated circuits is to create reference voltages and currents with well defined values. To accomplish this on-chip, so called bandgap reference circuits are commonly used. A typical application for reference voltages is in analog-to-digital conversion, where the input voltage is compared to several reference levels in order to determine the corresponding digital value. The emphasis in this thesis work lies on theoretical understanding of the performance limitations as well as the design of a bandgap reference circuit, BGR.</p><p>In this project, a comprehensive study of bandgap circuits is done in the first stage. Then investigations on parameter variations like Vdd, number of bipolars, W/L of PMOS, DC gain of Opamp, RL and CL are done for a PTAT current generator circuit. This PTAT current generator circuit is a part of the implemented BGR circuit based on [10], which is capable of producing an output reference voltage of 0.75 V when the supply voltage is 1 V. All of these circuits are implemented in a 0.35u CMOS technology.</p>

An important part in the design of analog integrated circuits is to create reference voltages and currents with well defined values. To accomplish this on-chip, so called bandgap reference circuits are commonly used. A typical application for reference voltages is in analog-to-digital conversion, where the input voltage is compared to several reference levels in order to determine the corresponding digital value. The emphasis in this thesis work lies on theoretical understanding of the performance limitations as well as the design of a bandgap reference circuit, BGR. In this project, a comprehensive study of bandgap circuits is done in the first stage. Then investigations on parameter variations like Vdd, number of bipolars, W/L of PMOS, DC gain of Opamp, RL and CL are done for a PTAT current generator circuit. This PTAT current generator circuit is a part of the implemented BGR circuit based on [10], which is capable of producing an output reference voltage of 0.75 V when the supply voltage is 1 V. All of these circuits are implemented in a 0.35u CMOS technology.

In the field of organic solar technology, there are two main problems, the stability of materials and the low power efficiency. By analyzing the power efficiency of organic solar cells, we can infer that efficiency of absorption and charge mobility are the key factors to these two problems. In this study, we focus on coupling carbazole with different low bandgap moieties. By using Suzuki Coupling, we synthesized new conjugated polymers with main chain structures of D-A sequence. It turns out that the copolymer can form a strong intramolecular charge transfer (ICT). We¡¦ve successfully synthesized two new low bandgap copolymers with D-A sequence, PCAMDT and PCAMDP. These two copolymers show us excellent thermal stabilities with decomposition temperature of 320¢Jand 355¢J,respectively.According to UV-Vis absorption spectrum, PCAMDT and PCAMDP own bandgaps at 1.85 eV and 2.22eV,respectively. Electrochemical analysis reveals that the HOMO and LUMO level of PCAMDT are found to be -5.69eV and -3.77eV,repectively, while the HOMO and LUMO level of PCAMDP are -5.87eV and -3.75eV. These properties make PCAMDT and PCAMDP advantageous materials while applied as high absorbing layers of organic solar cells.

Filling the liquid crystals (LCs) into the air holes of the photonic crystal fibers (PCFs), we can obtain the liquid-crystal photonic crystal fibers (LCPCFs). Due to the tunable optical properties of the LCs, we can fabricate tunable optical devices based on the LCPCFs. In this thesis, we investigate the photonic bandgap (PBG) properties and find out the effective modal index curves of the LCPCFs by the finite-difference frequency-domain (FDFD) method. The effects of the operation temperature and the alignment of the LCs are discussed. When the alignment of the LC is in the transverse plane of the PCF, we can observe the blue shift and the splitting of the PBGs as we increase the operation temperature. As the LC is aligned along the PCF, the red shift occurs and the splitting disappears. The shift and the splitting of the PBGs are due to the high anisotropic property of the LCs. Besides, we can rotate the alignment of the LCs by the external electric field, and the effects of the alignment on the propagation properties of the LCPCFs are larger than those of the operation temperature. In the experiment, we successfully fabricate the LCPCFs by using the vacuum method. In the measurement of the LCPCF at different operation temperatures,the red shift of the spectra can be observed with the increasing operation temperatures, which has a very good agreement with the simulation results. As we vary the alignment of the LCs with the external electric field, the transmission bands are almost the same as the voltage is less than 200V. During the range of 200V to 400V, the PBGs demonstrate obvious variations and the deep appears at 1050nm. When the external electric field is raised to 400V, the shapes of the spectra are almost the same and the red shift of the PBGs can be observed. The results of our simulation and the experiment measurement can help us to design and fabricate optical devices based on the LCPCFs.

Defect control in colloidal crystals is essential for these nanostructures to be effective as photonic bandgap (PBG) materials. We have used in-situ monitoring of the PBG of a colloidal crystal to study the structural changes during colloidal self assembly, with a focus on the formation of macroscopic defects such as cracks. These findings allow us to model the final stages of colloidal self assembly and explain the formation of growth defects in colloidal crystal. Our model suggests that cracks are intrinsic to self assembly growth methods. . However, by tuning the interaction potential between the colloids, it is possible to minimize the cracks in colloidal crystals. / Singapore-MIT Alliance (SMA)

For III-nitride wide-bandgap materials, the lack of efficient p-type wide bandgap semiconductors limits the full potential of group-III nitride-based optoelectronic devices. Conventional wide bandgap p-type materials consisting of magnesium-doped gallium nitride (GaN:Mg) and magnesium-doped aluminum gallium nitride (AlGaN:Mg) typically exhibit low hole carrier concentrations of <1018 cm-3 . Hence, I used different wide bandgap inorganic p-type materials as a promising solution, e.g., copper thiocyanate (CuSCN). CuSCN has multiple attractive properties that hold potential for applications in III-nitride materials. For example, its energy band gap is up to 3.9 e.V and its electron effective mass is higher than its hole effective mass. These two key features make CuSCN a potential wide bandgap p-type material for III-nitride systems. By exposing CuSCN to chlorine, Cl2-infused CuSCN thin film achieves a hole concentration up to 3 × 1018 cm-3 and maintains its visible-light-blind optical properties. Based on these desirable features, p CuSCN/n-GaN heterojunction ultraviolet photodetectors, as well as the p-CuSCN and n GaN interface, were fabricated to investigate the potential applications of p-CuSCN in III nitride devices. Moreover, p-CuSCN also benefits the corresponding organic solar cells; p CuSCN-based organic solar cells perform better in power conversion efficiency and stability tests under various conditions than intrinsic CuSCN-based organic solar cells. This work on p-CuSCN not only paves the way for new III-nitride semiconductor devices, but may also potentially enable the development of organic devices with better performance and longer lifetime. To explore the potential of transition metal oxides in UV photodetectors, NiO was selected to proceed with device fabrication because of its wider energy bandgap and lower hole effective mass than other transition metal oxides. Since single crystal quality is required to maintain its visible-light-blind optical property, brand-new templates were invented to grow single-crystal NiO thin films, TiN/MgO, and TiN/Si. Use of TiN thin film between NiO and the substrates provides a good back-side metal contact for NiO-based semiconductor devices. Several tools were employed to ascertain the single-crystal quality of as-grown NiO thin films on TiN/MgO and TiN/Si. I demonstrate NiO/TiN/MgO and NiO/TiN/Si bilayer structures may pave the way towards better NiO-based ultraviolet optoelectronic devices.