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The characterization of 2,3,6,7,10,11-hexabromotriphenylene, Br6TP, is presented toward its potential use as an n-type organic semiconductor and metal-free room temperature phosphor. The crystal structure shows both anisotropic two-dimensional BrBr interactions and inter-layer ?-stacking interactions. Photophysical characteristics were evaluated using solid-state photoluminescence and diffuse reflectance spectroscopies, revealing significantly red-shifted excitations in the visible region for the yellow solid material (compared to ultraviolet absorption bands for the colorless dilute solutions). Correlation of spectral, electrochemical, and computational data suggest the presence of an n-type semiconducting behavior due to the electron-poor aromatic ring. The material shows excellent thermal stability as demonstrated by thermogravimetric analysis and infrared spectra of a thin film deposited by thermal evaporation. The potential for Br6TP and its analogues toward use in several types of photonic and electronic devices is discussed.

This report describes the development of a computer model for the design of a laser seeker optical system. A laser seeker is a device that detects pulsed laser energy. The computer model is configured to design the seeker optics based on the following performance criteria: Sensitivity to laser energy, which can be related to target acquisition range; optical field of view; and seeker optics cross section area. The design is defined by four variables and a set of fixed parameters, and is configured using computer optimization with both a direct search and a random search being used. A superior design is selected from comparison of many sets of variables based on the value of an objective function made up of some of all of the performance criteria listed above and additional penalty factors applied for design constraint violations. The computer model contains design blocks for the detector, the preamplifier, and the optical elements of the seeker. There is also a computer ray trace routine to evaluate optical performance. The model was run with roar different objective functions, and the resulting seeker designs were analyzed. A detail listing of the computer program is contained in Appendix B.

Graphene has emerged as an appealing material for a variety of optoelectronic applications due to its unique electrical and optical characteristics. In this thesis, I will present recent advances in integrating graphene and graphene-boron nitride (BN) heterostructures with confined optical architectures, e.g. planar photonic crystal (PPC) nanocavities and silicon channel waveguides, to make this otherwise weakly absorbing material optically opaque. Based on these integrations, I will further demonstrate the resulting chip-integrated optoelectronic devices for optical interconnects. After transferring a layer of graphene onto PPC nanocavities, spectral selectivity at the resonance frequency and orders-of-magnitude enhancement of optical coupling with graphene have been observed in infrared spectrum. By applying electrostatic potential to graphene, electro-optic modulation of the cavity reflection is possible with contrast in excess of 10 dB. And furthermore, a novel and complex modulator device structure based on the cavity-coupled and BN-encapsulated dual-layer graphene capacitor is demonstrated to operate at a speed of 1.2 GHz. On the other hand, an enhanced broad-spectrum light-graphene interaction coupled with silicon channel waveguides is also demonstrated with ∼0.1 dB/μm transmission attenuation due to graphene absorption. A waveguide-integrated graphene photodetector is fabricated and shown 0.1 A/W photoresponsivity and 20 GHz operation speed. An improved version of a similar photodetector using graphene-BN heterostructure exhibits 0.36 A/W photoresponsivity and 42 GHz response speed. The integration of graphene and graphene-BN heterostructures with nanophotonic architectures promises a new generation of compact, energy-efficient, high-speed optoelectronic device concepts for on-chip optical communications that are not yet feasible or very difficult to realize using traditional bulk semiconductors.

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

by Hiu-suen Choy. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves [124]-131). / Acknowledgements / Abstract / Chapter Chapter 1 --- Introduction --- p.1-1 / Chapter Chapter 2 --- Basic Theory for MSM Photodetectors --- p.2-1 / Chapter 2.1 --- Schottky-Mott Theory for Ideal metal-Semiconductor Contact --- p.2-1 / Chapter 2.2 --- Modifications to Schottky-Mott Theory for Practical Metal Semiconductor Contact --- p.2-4 / Chapter 2.3 --- Energy Band of Metal-semiconductor-metal (MSM) Structures --- p.2-6 / Chapter 2.4 --- Dark Current Voltage Characteristics for MSM Structure --- p.2-12 / Chapter 2.5 --- Capacitance for Interdigitated MSM Photodetectors --- p.2-16 / Chapter 2.6 --- Basic mechanism of the MSM Photodetector --- p.2-19 / Chapter 2.7 --- DC Responsity and Quantum Efficiency of the Interdigitated MSM Photodetector --- p.2-20 / Chapter 2.8 --- Speed Performance of the Interdigitated MSM Photodetector --- p.2-21 / Chapter Chapter 3 --- Device Fabrication and Packaging --- p.3-1 / Chapter 3.1 --- Metallization Pattern --- p.3-1 / Chapter 3.2 --- Device Fabrication --- p.3-7 / Chapter 3.3 --- Device Packaging --- p.3-8 / Chapter Chapter 4 --- Experimental Description --- p.4-1 / Chapter 4.1 --- Experimental Procedures --- p.4-1 / Chapter 4.2 --- Equipment Description --- p.4-3 / Chapter Chapter 5 --- 1.3μm In0.53Ga0.47As Metal-Semiconductor-Metal Photodetector Grown by Low-Pressure MOCVD Using Tertiarybutylarsine --- p.5-1 / Chapter 5.1 --- General Description --- p.5-1 / Chapter 5.2 --- Structure of the Photodetector --- p.5-2 / Chapter 5.3 --- Experimental Results --- p.5-6 / Chapter 5.4 --- Data Analysis and Discussion --- p.5-14 / Chapter 5.5 --- Summary --- p.5-24 / Chapter Chapter 6 --- The Performance of 0.85μm Semi-Insulated GaAs MSM Photodetector with Different Interdigitated Spacings --- p.6-1 / Chapter 6.1 --- General Description --- p.6-1 / Chapter 6.2 --- Experimental Results --- p.6-2 / Chapter 6.3 --- Data Analysis and Discussion --- p.6-17 / Chapter 6.4 --- Summary --- p.6-27 / Chapter Chapter 7 --- Optical Control of Polarity in Short Electrical Pulses Generated from Coplanar Waveguide MSM Photodetectors --- p.7-1 / Chapter 7.1 --- General Description --- p.7-1 / Chapter 7.2 --- "Structure, Fabrication and Experimental Set-up" --- p.7-1 / Chapter 7.3 --- Experimental Results --- p.7-4 / Chapter 7.4 --- Data Analysis and Discussion --- p.7-11 / Chapter 7.5 --- Applications --- p.7-18 / Chapter Chapter 8 --- Conclusion --- p.8-1 / References / Publications

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Arthur Douglas Fisher. / Ph.D.

Semiconductor devices based on III-V materials have been the focus of intense research due to their superior electron mobility and favorable energy direct bandgap which are applicable in infrared wavelength range optoelectronics and high speed electronic systems. The thesis presented here consists of two thrusts; the first focusing on infrared applications, and the second focusing on InP-based heterojunction bipolar transistors (HBTs). In the first thrust, we investigate type-II InAs/GaSb superlattice IR detector devices and the effect of substrate orientation on InSb and InAs nanostructure morphology. In the second thrust, we study InP-based high frequency HBTs. A low resistance InAs ohmic contact is demonstrated, and we presented along with a study of the crystalline qualities in GaAs0.5Sb0.5 films grown on tilted- axis InP substrates. Chapter 2 presents fabrication and characterization of two type-II superlattice structures with 15 monolayer (ML) InAs/12ML GaSb and 17ML InAs/7ML GaSb grown on GaSb (100) substrates by solid-source molecular beam epitaxy (MBE). The X-ray diffraction (XRD) measurements of both the 15ML InAs/12ML GaSb and 17MLInAs/7ML GaSb superlattices indicated excellent material and interface qualities. The cutoff wavelengths of 15ML InAs/12ML GaSb and 17ML InAs/7ML GaSb superlattices photodetectors were measured to be 6.6μm and 10.2μm, respectively. These different spectral ranges were achieved by growing alternating layers of varying thicknesses which allowed for bandgap engineering of the superlattices of InAs and GaSb. Lastly, a mid-IR type-II superlattice photodiode was demonstrated at 80K with a cutoff wavelength at 6.6µm. The device exhibited a near background limited performance (BLIP) detectivity at 80K and higher temperature operation up to 280K. In Chapter 3, we show that the (411) orientation, though not a naturally occurring surface, is a favorable orientation to develop a buffer layer into a super flat surface at a certain high growth temperature. The (411) surface is a combination of localized (311) and (511) surfaces but at a high growth temperature, adatoms can obtain enough energy to overcome the energy barrier between these localized (311) and (511) surfaces and form a uniform (411) surface with potential minima. This results in a super flat surface which is promising for high-density nanostructure growth. In this work, this is the first time that the highest InSb and InAs nanostructures density can be achieved on the (411) surface which is in comparison with the (100), (311), and (511) surfaces. Chapter 4 of this thesis addresses the use of an InAs layer as a low-resistance ohmic contact to InP-based heterostructure devices. Selective area crystal growth of InAs on a dielectric (Benzocyclobutene, BCB polymer) covered InP (100) substrate and direct growth of InAs on InP substrate were performed by MBE. Heavy doping of InAs using Te was carried out to determine the lowest sheet resistance. Based on scanning electron microscope (SEM) and XRD measurements, increasing substrate temperature from 210 ℃ to 350 ℃, led to an improvement in crystallinity from a polycrystalline layer to a single crystal layer with a corresponding improvement of surface morphology. Moreover, a narrow X-ray diffraction peak indicated full-relaxation of the inherent 3.3% lattice-mismatch in InAs/InP layers. Furthermore, around 290 ℃ a tradeoff was reached between crystallinity and optimized dopant incorporation of Te into InAs for the lowest sheet resistance. Lastly, Chapter 5 discusses the effect of substrate tilting on the material properties of MBE grown GaAsSb alloys closely lattice-matched to an InP substrate. InP(100) substrates tilted 0°off-(on-axis), 2°off-, 3°off-, and 4°off-axis were used for MBE growth; then the material qualities of GaAsSb epitaxial layers were compared using various techniques, including high resolution XRD, photoluminescence (PL) and transmission-line measurements (TLM). Substrate tilting improved the crystalline quality of the GaAsSb alloys, as shown by a narrower XRD linewidth and enhanced optical quality as evidenced by a strong PL peak. The results of TLM show that the lowest sheet resistance was achieved at a 2° off-axis tilt.

Nearly 50 million people are afflicted with epilepsy, worldwide. These patients suffer from unprovoked seizures, where neurons in the cerebral cortex under go uncontrolled, hypersynchronous firing of neurons. 30\% of patients with epilepsy do not respond to drug treatments. For these patients, surgical treatment involving the removal or disconnection of brain matter is one of the only alternatives. Such surgical treatments often rely on long-term monitoring of neuronal activity in the brain using subdurally implanted surface electrodes to locate the epileptic focus, but these clinical methods for mapping neuronal activity suffer from low spatial resolutions and poor noise, which can limit the success of surgical treatments where an error of even 1 mm can be critical. The work described here involves the development of an implantable system for performing optical recordings of intrinsic signal (ORIS) on the surface of the brain. By taking advantage of the unique absorption spectrum of hemoglobin, cerebral blood volume (CBV) can be measured via reflectivity changes in the brain at at specific wavelengths of light. Due to the metabolic demands of the brain, the exaggerated neuronal activity and spiking associated with epileptic seizures can be detected indirectly through changes in CBV. While high resolution ORIS measurements have been recorded using externally mounted CCD sensors, this work presents some of the first developments in producing a fully implantable ORIS sensor. Progress in the development of an implantable ORIS sensor described here includes: an implantable organic light emitting diode (OLED) and organic photodetector (OPD) integrated on a highly flexible parylene-c substrate, an implantable sensor using a microLED array embedded on a flexible polyimide substrate, and the application of quantum dots to microLEDs for optical down-conversion. Successful in vivo detection of seizures is achieved with high signal-to-noise using these methods. Additionally, spatial localization of seizure activity is performed using the microLED array. These developments represent crucial first steps in the development of a full 2D neuronal mapping system using implantable ORIS devices.

1. Gain modulation induced by the injected optical signals in Semiconductor Optical Amplifier (SOA) is the basis of the whole work in this thesis. For a good understanding of the gain dynamics in SOA, we studied the propagation of lightwave and the carrier density dynamics in SOAs. Detailed theory and simulation results about the gain modulation characteristics induced by the injected signals into the SOA are presented. The simulation results have a good guidance for the experiments in this thesis. / 2. The theory of the actively mode-locked ring laser is studied. Following the theoretical discussion about the actively mode-locked ring laser, the experimental study about a novel actively mode-locked ring laser based on cross-gain-modulation in a SOA, which is employed as both the gain medium and mode-locking element, is proposed and demonstrated. Stable uniform pulse trains with pulse-widths about 24ps at 5GHz repetition frequency are obtained. The wavelength of the mode-locked optical pulses can be continuously tuned from 1533nm to 1565nm. In the whole tuning range, the pulse-width and bandwidth of the output pulses are respectively within 22-26ps and 0.7-0.8nm. / 3. Generation and wavelength switching of picosecond pulses by optically modulating a SOA in a ring laser with eight cascaded fiber Bragg gratings playing the role of the wavelength selecting element is proposed and demonstrated. Stable amplitude equalized pulse trains with a pulsewidth about 43ps at 2.5GHz have been obtained by injecting optical control signals into the laser. When we change the modulation frequency of the injected optical signals from 2.5 GHz to 10 GHz, wavelength switchable optical pulses at 10 GHz have also been obtained through optimizing the experimental parameters such as the SOA driving current and the power of the injection optical signals. Wavelength switching among eight wavelengths is achieved by merely tuning an intra-cavity optical delay line. The theoretical analysis of multi-wavelength operation using the proposed ring cavity has also been presented. / 4. In the actively mode-locked ring laser based on 1.55mum SOA, there exist changes of both gain and refractive index since the wavelengths of the control signal and the data signal are in the same gain spectral region. The gain change is sometimes unwanted because it may result in the amplitude fluctuations of the mode locked pulses and pattern effects. We proposed an all-optical FM actively mode-locked ring laser scheme based on a 1.3mum SOA as a gain-transparent phase modulation only element. The principle of the phase modulation in 1.3mum SOA has been discussed. / 5. Optical clock recovery, which extracts a continuous train of pulses or clock from the modulated data, is an essential technology to realize all optical signal processing such as all optical regeneration repeater and all optical de multiplexing. We experimentally studied all optical clock recovery at 10GHz with switchable wavelengths using the proposed mode-locked ring laser. Very stable clock signals corresponding to the bit rate of the injection data have been obtained by injecting 10Gbit/s 231-1 PRBS data signals into the laser cavity. The side-mode-suppression ratio of the recovery clock signals is better than 28dB. The clock recovery scheme can still function well when the wavelength, polarization state and the density of zeros of the injected data signals are changed. / 6. Finally, we discussed the noises in all optical networks and all optical methods of noise reduction. All optical noise reduction methods are reviewed. We also discussed the feasibility of all optical noise reduction method using the proposed ring laser scheme. / With the advances in Dense Wavelength Division Multiplexing (DWDM) and Optical Time Division Multiplexing (OTDM) technologies and their ever-widening applications, optical transport networks will eventually evolve into all optical networks based on DWDM and OTDM or their combination. However, the adoption of optical technologies has a significant impact on network transmission performance because there will be many optical amplifiers, wavelength division multiplexing devices and optical cross connects which may bring optical noises and time jitters to the all optical networks. Hence many key technologies including the generation of ultrashort optical pulses and all optical signal regeneration are needed in order to realize all optical transport networks. This dissertation mainly describes the generation of optical pulses and all optical clock recovery for all optical signal regeneration. Several theoretical and experimental research results have been obtained as follows. / He Jian. / "April 2006." / Adviser: K. T. Chan. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6610. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.