Sensing systems for mid-infrared wavelengths (2 to 5 μm) have important applications in biomedical, atmospheric and process gas monitoring systems. For lack of a suitable substrate, the full potential of GaSb-based materials, which are particularly suitable for operating in these wavelengths, are not completely realized. Hence, metamorphic growth technology, that allows the growth of semiconductor epilayers of arbitrary composition on any substrate, has been explored for antimony materials in this research. This makes the growth of device layers, containing arbitrary composition of GaSb-based materials, possible on commercially available 6"-GaAs substrates, and thereby reducing fabrication cost. Metamorphic growth of In(0.15)Ga(0.85)Sb was achieved using gas-source molecular beam epitaxy by growing compositionally graded ln(x)Ga(1-x)Sb buffer layers on a GaSb substrate. The effects of growth temperature on the quality of the metamorphic buffer layers along with the etching issues (both wet and dry) of GaSb-based materials were studied. Homo-junction n-i-p and p-i-n diodes were fabricated on In(0.15)Ga(0.85)Sb metamorphic layers. The dark current and its temperature dependence were measured and the extraction of area and perimeter components of dark current was done. The modeling of the components of dark current suggests that the diode currents were dominated by surface leakage. Surface passivation by silicon nitride and polyimide were investigated and our findings suggest that the former resulted in a better passivated surface. Responsivity measurements show that In(0.18)Ga(0.82)Sb diodes, metamorphically grown on GaSb substrates, have a cut-off wavelength of 2270 nm. Finally, hole (β) and previously unreported electron (α) ionization coefficients, at room temperature and 90° C, were extracted from these structures. The results show that α>β for ln(0.10)Ga(0.90)Sb for both temperatures. These photodetectors can be implemented m practical receiver systems for mid-infrared applications, such as atmospheric CO2 and methane detection at 2.0 μm. The possibility of growing antimony-based device layers on larger substrates, paves the way for future optoelectronic receiver systems operating at longer wavelengths, where both the photodetector and the amplifier can be integrated in the same module. / Thesis / Doctor of Philosophy (PhD)

This thesis presents the development of integrated silicon photonic devices. These devices are compatible with the present and near future CMOS technology. High-khorizontal grating couplers and waveguides are proposed. This work consists of simulations and device design, as well as the layout for the fabrication process, device fabrication, process development, characterization instrument development and electro-optical characterizations. The work demonstrates an alternative solution to costly silicon-on-insulator photonics. The proposed solution uses bulk silicon wafers and thin film deposited waveguides. Back-end deposited horizontal slot grating couplers and waveguides are realized by multi-layers of amorphous silicon and high-k materials. The achievements of this work include: A theoretical study of fully etched slot grating couplers with Al2O3, HfO2 and AIN, an optical study of the high-k films with spectroscopic ellipsometry, an experimental demonstration of fully etched SiO2 single slot grating couplers and double slot Al2O3 grating couplers, a practical demonstration of horizontal double slot high-k waveguides, partially etched Al2O3 single slot grating couplers, a study of a scheme for integration of the double slot Al2O3  waveguides with selectively grown germanium PIN photodetectors, realization of test chips for the integrated germanium photodetectors, and study of integration with graphene photodetectors through embedding the graphene into a high-k slot layer. From an application point of view, these high-k slot waveguides add more functionality to the current silicon photonics. The presented devices can be used for low cost photonics applications. Also alternative optical materials can be used in the context of this photonics platform. With the robust design, the grating couplers result in improved yield and a more cost effective solution is realized for integration of the waveguides with the germanium and graphene photodetectors. / <p>QC 20141114</p>

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No description available.

Fourier Transform Infrared spectroscopy is used as a diagnostic tool in biological and physical sciences by characterizing the samples based on infrared light-matter interaction. In the case of biological samples, Activation of Jurkat T-cells in culture following treatment with anti-CD3 (Cluster of Differentiation 3) antibody is detectable by interrogating the treated T-cells using the Attenuated Total Reflection - Fourier Transform Infrared (ATR-FTIR) Spectroscopy technique. Cell activation was detected within 75 minutes after the cells encountered specific immunoglobulin molecules. Spectral markers noted following ligation of the CD3 receptor with anti CD3 antibody provides proof-of-concept that ATR-FTIR spectroscopy is a sensitive measure of molecular events subsequent to cells interacting with anti-CD3 Immunoglobulin G (IgG). ATR-FTIR spectroscopy is also used to screen for Colitis in chronic (Interleukin 10 knockout) and acute (Dextran Sodium Sulphate-induced) models. Arthritis (Collagen Antibody Induced Arthritis) and metabolic syndrome (Toll like receptor 5 knockout) models are also tested as controls. The marker identified as mannose uniquely screens and distinguishes the colitic from the non-colitic samples and the controls. The reference or the baseline spectrum could be the pooled and averaged spectra of non-colitic samples or the subject’s previous sample spectrum. The circular dichroism of titanium-doped silver chiral nanorod arrays grown using the glancing angle deposition (GLAD) method is investigated in the visible and near infrared ranges using transmission ellipsometry and spectroscopy. The characteristics of these circular polarization effects are strongly influenced by the morphology of the deposited arrays. Studies of optical phonon modes in nearly defect-free GaN nanowires embedded with intrinsic InGaN quantum dots by using oblique angle transmission infrared spectroscopy is described here. These phonon modes are dependent on the nanowire fill-factor, doping densities of the nanowires and the presence of InGaN dots. These factors can be applied for potential phonon based photodetectors whose spectral responses can be tailored by varying a combination of these three parameters. The optical anisotropy along the growth (c-) axis of the GaN nanowire contributes to the polarization agility of such potential photodetectors.

Semiconductor nanowires acts as an emerging class of materials with great potential for applications in future electronic devices. Small size, large surface to volume ratio and high carrier mobility of nanowires make them potentially useful for electronic applications with high integration density. In this thesis, the focus was on the growth of high quality ZnO nanowires, fabrication of field effect transistors and UV- photodetectros based on them. Intrinsic nanowire parameters such as carrier concentration, field effect mobility and resistivity were measured by configuring nanowires as field effect transistors. The main contribution of this thesis is the development of a high gain UV photodetector. A single ZnO nanowire functioning as a UV photodetector showed promising results with an extremely high spectral responsivity of 120 kA/W at wavelength of 370 nm. This corresponds to high photoconductive gain of 2150. To the best of our knowledge, this is the highest responsivity and gain reported so far, the previous values being responsivity=40 kA/W and gain=450. The enhanced photoconductive behavior is attributed to the presence of surface states that acts as hole traps which increase the life time of photogenerated electrons raising the photocurrent. This work provides the evidence of such solid states and preliminary results to modify the surface of ZnO nanowire is also produced.

[pt] As tecnologias envolvendo detectores de infravermelho são consideradas de emprego dual, ou seja, podem ser empregadas tanto no meio civil quanto no militar. No meio civil, tais detectores podem ser utilizados como meio auxiliar na formulação de diagnósticos médicos, em inspeções de rotina nas indústrias, no controle de pragas da agricultura etc.. E no meio militar os equipamentos envolvendo detectores de infravermelho (visão noturna) são comumente empregados em situações táticas, com o objetivo de se obter uma situação de vantagem sobre o inimigo. Esta dissertação teve por objetivo avaliar de forma sistemática o desempenho de detectores de infravermelho baseados na heteroestrutura de poços quânticos múltiplos de InGaAs/InAlAs ao se variar a densidade do elemento dopante (silício) no poço. Em um reator do tipo MOVPE foi realizado o crescimento epitaxial das heteroestruturas que foram caracterizadas de acordo com as técnicas de difração de raios X, efeito Hall, fotoluminescência e absorção. Em seguida, elas foram processadas, tomando forma de dispositivo. A partir da caracterização do dispositivo final, com base nas principais figuras de mérito de um fotodetector (corrente de escuro, fotocorrente, responsividade e detectividade), foi possível obter conclusões importantes a respeito da influência da dopagem em poços quânticos no desempenho de fotodetectores do tipo QWIPs (Quantum Well Infrared Photodetectors). / [en] Infrared detectors are considered of dual employment technologies, ie they can be employed both in the civilian and military environment. With respect to the civilian environment, such detectors can be used, among other applications, as an auxiliary device in the formulation of medical diagnoses, on the routine inspection in industries, in pests control in agriculture and so on. Military applications involving infrared detectors (night vision) are commonly tactical situations, when they are employed in order to get an advantage over the enemy. The main motivation of the present work is the systematical evaluation of the performance of infrared detectors based on the multiple quantum wells heterostructure of InGaAs /InAlAs, varying the density of the doping element (silicon) into the well. The epitaxial growth of the heterostructures was performed in a MOVPE reactor. Afterwards, they were characterized in accordance with X-ray diffraction, Hall effect, photoluminescence and absorption techniques. Finally, they were processed, achieving a devices form. Based on the characterization of the final device, that took into consideration the key figures of merit of a photodetector (dark current, photocurrent, responsivity and detectivity), it was possible to obtain important conclusions about the quantum well doping effects on the QWIPs (Quantum Well Infrared Photodetectors) performance.

[pt] Pontos quânticos (PQs) auto-organizáveis de InAs sobre InP, InGaAs, InGaAlAs utilizando-se substratos de InP foram crescidos pela deposição química de metal-orgânicos (MOCVD) e foram investigadas para fotodetectores. Para PQs de InAs crescidos sobre diferentes substratos de InP, têm-se que a presença de discordâncias é responsável pelo aumento na densidade planar dos PQs. O espectro de fotoluminescência (FL) das estruturas de InP/InxGa1-xAs/InAs/InP, com diferentes composições da camada ternária. Medidas com microscopia de força atômica (AFM) mostraram que os PQs mais altos são obtidos quando os mesmos são crescidos sobre uma camada de InxGa1-xAs com um descasamento de 1000ppm, e a altura decresce com o descasamento a partir deste valor. O espectro de FL dos PQs mostrou uma banda assimétrica, a qual envolve transições entre os níveis de energia dos PQs e pode ser decomposta em dois picos. Pico de energia mais alta desta banda foi observado para a amostra com PQs crescidos sobre uma camada de InxGa1-xAs casada e o pico foi deslocado para energias mais baixas para amostras tensionadas. Estruturas diferentes de PQ de InAs crescidas sobre uma camada de InGaAlAs casada com InP foram investigadas. Picos de fotocorrente extremamente estreitos foram observados, demonstrando um excelente potencial para sintonização estreita de comprimentos de onda. Foram desenvolvidas estruturas para detectar radiação superior à 10μm. Medidas de absorção mostrando uma dependência com a polarização mostraram eu as estruturas tem um confinamento total e são apropriadas para detecção sintonizável de radiação por incidência normal. / [en] Self-assembled InAs quantum dots (QD) over an InP, InGaAs, InGaAlAs on InP substrates were grown by metal-organic chemical vapor deposition (MOCVD) and were investigated for quantum dot infrared photodetectors. For InAs QD over an InP buffer on different InP substrates. The results indicate that the presence of dislocations were responsible for the increase in the QD density. Photoluminescence (PL) spectra of InP/InxGa1-xAs/InAs/InP dot-in-a-well structures, with different compositions of the ternary layer. Measurements with atomic force microscopy showed that the largest QD height is obtained when the InAs QDs are grown on the InxGa1-xAs layer with a mismatch of 1000ppm, and the height decreases as the mismatch departs from this value. PL spectra of the QDs showed an asymmetric band, which involves transitions between dot energy levels and can be deconvoluted into two peaks. The highest energy PL peak of this band was observed for the sample with the QDs grown on top of the lattice-matched InxGa1-xAs and it shifted to lower energies for strained samples as the degree of mismatch increased. Different InAs quantum dot structures grown on InGaAlAs lattice matched to InP. Extremely narrow photocurrent peaks were observed, demonstrating great potential for fine wavelenght selection. Structures which can detect radiation beyond 10ìm were developed. Polarization dependence measurements showed that the structures have a zero- dimensional character and are suitable for detection of normal incidence light.

Solar cells and photodetectors rely on similar physical principles based on the interaction of light and matter. Both types of optoelectronic devices are indispensable in a wide range of technological applications, from large-scale renewable power conversion to everyday consumer items. In this thesis, the use of facile solution-processable semiconductors in solar cells and light sensors is studied with a focus on antimony sulfide (Sb₂S₃) and antimony sulfoiodide (SbSI). The improvement of the photovoltaic performance in Sb₂S₃ sensitized solar cells upon the controlled partial oxidation of the absorber layer is investigated. A reduction in charge carrier recombination is the reason for the improved efficiency, caused by the oxidation process. Further, a new chemical bath deposition method for antimony sulfide is developed. Carried out at room temperature, this technique eliminates the necessity of cooling equipment during the deposition process. The antimony sulfide from this method decreases the density of trap states compared to the conventional deposition. Power-conversion efficiencies of up to η=5.1% are achieved in antimony sulfide sensitised solar cells using the new room temperature deposition method. Finally, antimony sulfide is used as a precursor to form films of antimony sulfoiodide (SbSI) micro-crystals in a facile physical vapour process. These films are then used to fabricate photodetectors. With PMMA as an insulating spacer layer, the devices are built in a sandwich-type architecture. Optoelectronic characterisation shows that these devices have the shortest response and recovery times reported for SbSI photodetectors to date.

Neste trabalho desenvolvemos rotinas computacionais em Python para o cálculo de propriedades dinâmicas (espectros de fotocorrente e absorção) de heteroestruturas semicondutoras baseadas em Dinâmica Quântica. Em uma primeira etapa do desenvolvimento do projeto, a formulação baseada na evolução temporal das soluções da equação de Schrödinger dependente do tempo foi aplicada a sistemas com soluções analíticas conhecidas ou com resultados já reportados na literatura. Devido à excelente concordância entre nossos dados e aqueles já conhecidos, em uma etapa seguinte, foram calculadas as energias de transição observadas em espectros de fotoluminescência para poços quânticos de InGaAs/GaAs, crescidos por MBE, levando-se em conta os efeitos de tensão e segregação de átomos de índio. Na continuidade do projeto, especial atenção foi dada ao desenvolvimento de estratégias para calcular os espectros de absorção e fotocorrente para dispositivos do Estado Sólido. O conjunto de resultados apresentados neste trabalho demonstra que a metodologia desenvolvida é precisa e pode ser utilizada com baixo custo computacional para o modelamento de heteroestruturas semicondutoras mais complexas, que servem de base para o desenvolvimento de dispositivos optoeletrônicos. / In this work we developed computational routines in Python for the calculation of the dynamic properties (spectrum of photocurrent and absorption) of semiconductor heterostructures based on Quantum Dynamics Theory. In a first stage of the development of the project the formulation based on the time evolution of the solutions of the time dependent Schrödinger equation was applied to systems with known analytical solutions or results already reported in the literature. Due to the excellent agreement between our data and those already known, in the next stage the transition energies observed in photoluminescence spectra for InGaAs/GaAs quantum wells, grown by MBE, were calculated taking into account the effects of stress and segregation of indium atoms. In the continuity of the project, special attention was given to the development of strategies to calculate absorption and photocurrent spectra for solid state devices. The set of results presented in this work demonstrates that the methodology developed is accurate and can be used with low computational cost for the modeling of more complex semiconductor heterostructures, which are used for the development of optoelectronic devices.