No description available.

Este trabalho teve como objetivo principal a fabricação de fotodetetores do tipo Metal-Semicondutor-Metal (MSM) com corrente de escuro da ordem de 1 nA, responsividade da ordem de 0,1 A/W e razão fotocorrente/corrente de escuro de pelo menos 10. Estes valores asseguram que os fotodetetores obtidos tenham sensibilidade suficiente para serem utilizados em sensores ópticos integrados. Todos os materiais utilizados na construção dos fotodetetores MSM são compatíveis com processos convencionais de fabricação em microeletrônica, facilitando a integração com outros dispositivos em estado sólido. O semicondutor utilizado nos fotodetetores foi o silício, na forma monocristalina ou policristalina. Como material de eletrodo, foi utilizado o alumínio, o titânio ou o níquel. No processo de fabricação básico, foram utilizados apenas três etapas: deposição do filme metálico, fotolitografia e corrosão, confirmando a simplicidade de fabricação desse fotodetetor. Através da construção de dispositivos com diferentes geometrias e diferentes combinações dos materiais citados acima, foi possível verificar a influência que a estrutura cristalina do semicondutor, tipo de dopagem do semicondutor, geometria e material de eletrodo tem sobre o desempenho e o comportamento dos MSMs. O comprimento de onda de 632,8 nm foi utilizado na caracterização dos dispositivos, devido a sua disponibilidade e o desenvolvimento de guias ópticos utilizando esse comprimento de onda em trabalhos anteriores do nosso grupo de pesquisa. Os melhores resultados obtidos foram com as amostras de Si monocristalino tipo-p com eletrodos de titânio. Na amostra sinterizada à 250°C foi obtido um valor da corrente de escuro de 4,8 nA e, na amostra de referência, foi obtido um valor de responsividade de 0,28 A/W. / The goal of this work was the fabrication of Metal-Semiconductor-Metal (MSM) photodetectors with the following characteristics: dark current of about 1 nA, responsivity of about 0.1 A/W and dark/photocurrent ratio of at least 10. These values ensure that the photodetectors have enough sensitivity to be used in integrated optic sensors. All materials used in the fabrication of the MSM are compatible with conventional microelectronic manufacture process, so that the photodetectors can be more easily integrated with other solid-state devices. The semiconductor used in the photodetectors was silicon, in single crystal and polycrystalline form. As material of electrodes, aluminum, titanium or nickel had been used. The basic fabrication process consists of only three steps: metal film deposition, photolithography and etching, which confirm the simplicity of the fabrication of this device. Building MSMs with different geometries and making combinations with the materials cited above, gave the possibility to verify the influence that crystalline structure of the semiconductor, doping type of the semiconductor, geometry and electrode material have on the behavior of the photodetectors. The wavelength of 632.8 nm was used in the characterization of the devices, due to its availability and the development of optic waveguides using this wavelength in previous works of our research group. The best results were obtained with the samples fabricated using single crystal Si p-type with titanium electrodes. The sample annealed at 250°C had dark current value of 4.8 nA and, the reference sample had responsivity of 0.28 A/W.

Este trabalho teve como objetivo principal a fabricação de fotodetetores do tipo Metal-Semicondutor-Metal (MSM) com corrente de escuro da ordem de 1 nA, responsividade da ordem de 0,1 A/W e razão fotocorrente/corrente de escuro de pelo menos 10. Estes valores asseguram que os fotodetetores obtidos tenham sensibilidade suficiente para serem utilizados em sensores ópticos integrados. Todos os materiais utilizados na construção dos fotodetetores MSM são compatíveis com processos convencionais de fabricação em microeletrônica, facilitando a integração com outros dispositivos em estado sólido. O semicondutor utilizado nos fotodetetores foi o silício, na forma monocristalina ou policristalina. Como material de eletrodo, foi utilizado o alumínio, o titânio ou o níquel. No processo de fabricação básico, foram utilizados apenas três etapas: deposição do filme metálico, fotolitografia e corrosão, confirmando a simplicidade de fabricação desse fotodetetor. Através da construção de dispositivos com diferentes geometrias e diferentes combinações dos materiais citados acima, foi possível verificar a influência que a estrutura cristalina do semicondutor, tipo de dopagem do semicondutor, geometria e material de eletrodo tem sobre o desempenho e o comportamento dos MSMs. O comprimento de onda de 632,8 nm foi utilizado na caracterização dos dispositivos, devido a sua disponibilidade e o desenvolvimento de guias ópticos utilizando esse comprimento de onda em trabalhos anteriores do nosso grupo de pesquisa. Os melhores resultados obtidos foram com as amostras de Si monocristalino tipo-p com eletrodos de titânio. Na amostra sinterizada à 250°C foi obtido um valor da corrente de escuro de 4,8 nA e, na amostra de referência, foi obtido um valor de responsividade de 0,28 A/W. / The goal of this work was the fabrication of Metal-Semiconductor-Metal (MSM) photodetectors with the following characteristics: dark current of about 1 nA, responsivity of about 0.1 A/W and dark/photocurrent ratio of at least 10. These values ensure that the photodetectors have enough sensitivity to be used in integrated optic sensors. All materials used in the fabrication of the MSM are compatible with conventional microelectronic manufacture process, so that the photodetectors can be more easily integrated with other solid-state devices. The semiconductor used in the photodetectors was silicon, in single crystal and polycrystalline form. As material of electrodes, aluminum, titanium or nickel had been used. The basic fabrication process consists of only three steps: metal film deposition, photolithography and etching, which confirm the simplicity of the fabrication of this device. Building MSMs with different geometries and making combinations with the materials cited above, gave the possibility to verify the influence that crystalline structure of the semiconductor, doping type of the semiconductor, geometry and electrode material have on the behavior of the photodetectors. The wavelength of 632.8 nm was used in the characterization of the devices, due to its availability and the development of optic waveguides using this wavelength in previous works of our research group. The best results were obtained with the samples fabricated using single crystal Si p-type with titanium electrodes. The sample annealed at 250°C had dark current value of 4.8 nA and, the reference sample had responsivity of 0.28 A/W.

No description available.

A monolithically integrated broadly tunable MQW laser that utilizes a combined impurity-free vacancy disordering (IFVD) of quantum wells and optical beam steering techniques is proposed and investigated experimentally. The device consists of a beam-steering section and an optical amplifier section fabricated on a GaAs/AlGaAs quantum well (QW) p-i-n heterostructure. The beam steering section forms a reconfigurable optical waveguide that can be moved laterally by applying separately controlled electrical currents to two parallel contact stripes. The active core of the gain section is divided in into selectively intermixed regions. The selective intermixing of the QW in the gain section results in neighboring regions with different optical bandgaps. The wavelength tuning is accomplished by steering the amplified optical beam through the selected region where it experiences a peak in the gain spectrum determined by the degree of intermixing of the QW. The laser wavelength tunes to the peak in the gain spectrum of that region. The IFVD technique relies on a silica (SiO2) capped rapid thermal annealing and it has been found that the degree of intermixing of the QW with the barrier material is dependent on the thickness of the SiO2 film. The QW sample is first encapsulated with a 400nm thick SiO2 film grown by plasma enhanced chemical vapor deposition (PECVD). In the gain section, the SiO2 film is selectively etched using multiple photolithographic and reactive ion etching steps whereas the SiO2 film is left intact in all the remaining areas including the beam-steering section. The selective area quantum well intermixing is then induced by a single rapid thermal annealing step at 975°C for a 20s duration to realize a structure with quantum well that has different bandgaps in the key regions. Optical characterizations of the intermixed regions have shown a blue shift of peak of the electroluminescence emission of 5nm, 16nm and 33nm for the uncapped, 100nm and 200nm iv respectively when compared to the as grown sample. The integrated laser exhibited a wavelength tuning range of 17nm (799nm to 816nm). Based on the same principle of QW selective intermixing, we have also designed and fabricated a monolithically integrated multi-wavelength light emitting diode (LED). The LED emits multiple wavelength optical beams from one compact easy to fabricate QW structure. Each wavelength has an independent optical power control, allowing the LED to emit one or more wavelengths at once. The material for the LED is the same AlGaAs/GaAs QW p-i-n heterostructure described above. The device is divided into selectively intermixed regions on a single QW structure using IFVD technique to create localized intermixed regions. Two different designs have been implemented to realize either an LED with multiple output beams of different wavelengths or an LED with a single output beam that has dual wavelength operation capabilities. Experimental results of the multiple output beams LED have demonstrated electrically controlled optical emission of 800nm, 789nm and 772nm. The single output LED has experimentally been shown to produce wavelength emission of 800nm and/or 772nm depending on electrical activation of the two aligned intermixed regions.

The behaviour of electrons in nanostructures such as quantum wells is of interest for the design of new electronic and electro-optic devices, and also for exploration of basic many-body physics. This thesis develops and tests improved methods for describing such electronic behaviour. The system used for this work was the parabolic quantum well (PQW), an important special system which has recently attracted much experimental and theoretical attention. We firstly report self-consistent nonlinear groundstate solutions of the Poisson equation together with the Thomas-Fermi (TF) hydrostatic equations. In contrast to most previous solutions, all the electron density profiles were inhomogeneous and continuous. We also added a von Weizsacker term with and without the exchange/exchange-correlation to the above treatment, using a novel numerical approach allowing for wider electron gases than previously possible. We also report for the first time the effects of spatially varying effective mass and dielectric function in theories of this type. To investigate infrared response of these systems, we apply new hydrodynamic theories recently proposed by Dobson. By using this type of theory, we simultaneously satisfy the Harmonic Potential Theorem (extended generalized Kohn theorem) and obtain the correct 2D plasmon dispersion, as well as obtaining the correct spacing of standing plasmons. Other inhomogeneous hydrodynamic theories do not achieve this. We also showed analytically an exact solution for a plasmon mode at the Kohn frequency in addition to one found in the Harmonic Potential Theorem. An open hydrodynamic theory was then developed based on this type of mode. Numerical application of Kohn Frequency Theorem theory was shown and the results were compared with other existing hydrodynamic theories.

Fluorescence lifetime determination and allied studies find application in spectroscopy in general and fiber optic biosensors in particular. Instruments and sensors cited in literature however use open loop, intensity based techniques with sophisticated detectors and components. We propose phase sensitive signal processing schemes to estimate the fluorescence lifetime using simple detectors and components, without compromising on accuracy. The performance of the schemes proposed is analysed and contrasted from a communications (signals and systems) point of view. The resolution and sensitivity limits imposed in processing the signal, by systematic errors and additive noise, are derived for the schemes suggested. It is found that systematic errors impose a phase resolution limit of about 2°. We then study the suitability of different detectors and channels for application in phase sensitive fluorescence biosensors we analyse the effect of systematic limitations as well as additive noise, in the detection/transmission process, from the point of view of the components used. Certain fundamental limits of operation in terms of excitation intensities are derived for different detector-channel combinations, with a view to obtain a given resolution. A photodiode used with a fiber bundle is found to be sufficient for accurate phase read outs with 10"4 radians resolution. A PMT used in conjunction with a multimode fiber serves as a very good device for microsensing applications Lastly, the biosensor for oxygen sensing, the ruthenium complex, is studied for standardisation of the sensor. We examine the quenching of fluorescence, the repeatability and reusability of the sensor, the stability of the instrument and such.