¡uGaAs VCSEL Contact Process and Feature Analysis ¡vIn this article, we talk about the process of metalization on sample of epied GaAs VCSEL structure. We deposit Au/Ge-Au on n-GaAs substrate for n-type contact ¡Fand Au/Be-Au on p-DBR for p-type contact by thermal evaporation. To lower threshold current, and increase laser output power, ohmic contact is a necessary condition. Furthermore a lot of analysis is done for injection current-EL spectrum; VCSEL structure-EL spectrum; output aperture-laser output power. And check the laser mode with gain Spectrum ¡Bresonant cavity mode ¡B spontaneous emission of active layer. Throughout the analysis mention above, we hope to find a reasonable and reliable way of VCSEL structure design, so that we can reduce the heat effect to vertical cavity surface emitting laser.

Abstract A method using CFD-based computer simulations as a virtual reactor was proposed for cost-effective CVD reactor design. The virtual reactor was developed by combining the chemical reactor mechanism and rate constants obtained from kinetic studies using a small-scale, with the momentum, mass and heat transport processes simulated using a CFD code. The effect of the flow structure on the film thickness uniformity is demonstrated for the growth of GaAs from a Ga(CH3)3 -AsH3- H2 mixture. We present a modeling study of the growth of gallium arsenide layers deposited onto a high-temperature susceptor in a cylindrical metalorganic chemical vapor deposition reactor. We analyzed the deposition process with a two-dimensional model that is axisymmetric about the vertical axis. We attempted to control the extent of the consecutive reaction by modifying the flow pattern. For the output of side walls, because the gas velocity increase near the wafer edge, the residence time was lower in the central part of the wafer than near the edge. Therefore, it can be controlled by locating the outlet such that residence time above the entire wafer is uniform. And the study finds that decreasing the hole size lowered the film uniformity. This occurred because relative to the velocity at the center of the wafer, the velocity near the wafer edge increased with decreasing hole size. This result confirms that the control of the boundary layer thickness is very important for the film thickness uniformity. We also find that decreasing the shower-to-wafer distance increased velocity near the wafer and therefore increased the growth rate. The present study indicates that we can design a MOCVD reactor and optimize the operating conditions efficiently using a computer simulation with other¡¦s experiments.

The need of the everyday user to transfer large amounts of data is driving the need for larger data transfer capacity. Optical communication networks can satisfy this need. To be economically viable, optical transceivers must be integrated onto chips at low cost, using relatively cheap semiconductor processes. The optical preamplifier (transimpedance amplifier) receives optical information and converts it to a useful electrical form. It must operate at high speed, contribute little distortion to the input signal, and add little electrical noise to the incoming signal. This thesis investigates the design techniques in the literature, and proposes new architectures. Two high performance preamplifiers are designed, one using GaAs HEMTs, and the other using GaAs HBTs, each with different circuit techniques. The HEMT preamplifier has a transimpedance gain of 1.4 kΩ, the highest in the literature for 10 Gb/s operation, along with a low input referred noise current of about 15 pA/Hz1/2 at a bandwidth of 6.3 GHz. The HBT preamplifier also has a transimpedance gain of 1.5 kΩ, with a low input referred noise current of about 7 pA/Hz1/2. Both have clear, open eye-diagrams with a 10 Gb/s bit stream input, and are suitable for integration on a chip. The HEMT preamplifier was implemented as a common-gate, common-source amplifier cascade with a darlington output driver for a 50 Ω load. The HBT preamplifier was implemented as common-emitter darlington amplifier with shunt peaking, and a simple emitter degenerated output driver for a 50 Ω load. Both implementations exceeded the bandwidth, transimpedance gain and noise performance typically expected of the transistor technologies used. It is shown that the transimpedance limit can be circumvented by the use of novel architectures and shunt peaking.

In this study, the characteristics of atomic layer deposited TiO2 films on Gallium Arsenide substrate were investigated. The physical and chemical properties were measured and surveyed. And an Al/ALD-TiO2/GaAs MOS structure was used for the electrical characterizations. For the electrical property improvements, we investigated the atomic layer deposited TiO2 films by the (NH4)2Sx treatments for GaAs substrate. The leakage currents and the hysteresis loop flatband voltage shift can be improved for ALD-TiO2 films on S-GaAs. Furthermore, in order to resist the leakage current from the grain boundary of the polycrystalline TiO2 films, amorphous-like structure of TiO2 thinner films are investigated. The combination of sulfur passivation and amorphous-like structure thinner films is sufficient to improve the electrical properties effectively.

Due to the high electron mobility compared with Si, III-V compound semiconductors (GaAs) has been applied widely for high-speed devices. The titanium oxide (TiO2) has not only has high dielectric constant but has well lattice match with GaAs substrate. Therefore, the high-k material TiO2 was chosen to be the gate oxide in this study. The major problem of III-V compound semiconductors is known to have poor native oxide on it and leading to the Fermi level pinning at the interface between oxide and semiconductor. The C-V stretch-out phenomenon can be observed and the leakage current is high. The surface passivation of GaAs with (NH4)2Sx treatment (S-GaAs) can prevent it from oxidizing after cleaning and improve the interface properties. In order to passivate the grain boundary of polycrystalline ALD-TiO2 film and the interface state, the fluorine from liquid-phase- deposited SiO2 solution can achieve the goal effectively. In addition, the post-metallization annealing (PMA) is another efficiency way to improve the ALD-TiO2 film quality. The mechanism of PMA process is the reaction between the aluminum contact and hydroxyl groups existed on TiO2 film surface. Then the active hydrogen is produced to diffuse through the oxide and passivate the oxide traps.

No description available.

Double crystal x-ray topography using a synchrotron radiation source has been used to measure the lattice distortions present in 50mm diameter samples of (001) semi-insulating LEG gallium arsenide. Lattice strains and tilts have been mapped in In-doped and undoped samples as well as annealed and unannealed samples taken from the seed and tail ends of boules. The properties of the x-ray source which are necessary for these measurements are discussed and it is concluded that a synchrotron source is the only practical choice. Lattice strains of 90ppm and tilts greater than 100 arc seconds were measured in In-doped material both of which appear to be due to a combination of In concentration variations and the inhomogeneous dislocation distribution. Undoped samples were found to be more uniform with lattice strains of typically +20ppm towards the samples edges where the dislocation density is largest. The lattice tilt distribution in seed and undoped samples invariably exhibited a four-fold symmetry which was enhanced by the presence of lineage features lying along the <110> directions. Tail end samples were generally less uniform in lattice strain and showed a lower symmetry in their lattice tilts. These results are discussed in the light of current ideas concerning the origin of variations in lattice strain and EL2 concentration. An x-ray diffraction method involving integrated intensity measurements of the quasi-forbidden 200 reflection, which is highly stoichiometry sensitive, is investigated. The results, however, show no conclusive stoichiometry variations but do highlight important experimental conditions which must be satisfied if such measurements are to be meaningful. The images of dislocations in double crystal x-ray topographs are investigated and compared with theoretical simulations in order to assess the effects of point defect environment on the dislocation strain field. The results suggest that the EL2-dislocation interaction is not significantly strain driven.

Rapid Thermal Annealing has been used to study the electrical activation of a range of donor and acceptor species in ion-implanted GaAs. By varying the time and temperature of the post implant anneal, it was found that the activation processes for most implants can be characterised in terms of two distinct regions. The first of these occurs at short annealing times, where the electrical activity is seen to follow a time-dependent behaviour. At longer annealing times, however, a time-independent saturation value is reached, this value being dependent on the annealing temperature. By analysing the data from Be, Mg, S and Se implants in GaAs, a comprehensive model has been evolved for the time and temperature dependence of the sheet electrical properties. Application of this model to each of the ions studied suggests that the activation processes may be dominated by the extent to which ions form impurity-vacancy complexes. An analysis of the time-dependent regime also shows that, at short annealing times, the mobile species is more likely to be the substrate atoms (or vacancies) rather than the implanted impurities. In the time-dependent region, the values of diffusion energy were found to be between 2.3 to 3.0 eV for all ions, these values corresponding to a diffusion of Ga or As vacancies (or atoms). In the saturation region, activation energies of 0.3 to 0.4 eV and 1.0 to 1.2 eV were obtained for the activation processes of interstitial or complexed impurities respectively.

Dispositivos fotovoltaicos híbridos baseados em polímeros conjugados e semicondutores inorgânicos estão sendo utilizados nos últimos anos para a produção de células de energia solar com baixo custo. Para que haja uma alta eficiência é necessária dissociação eficiente de éxcitons, por isso é importante conhecer os níveis de energias dos componentes do dispositivo fotovoltaico. O presente estudos mostra que o sistema híbrido formado por nanofios cilíndricos preparados com heteroestrutura radial de camadas alternadas de GaAs/AlGaAs/GaAs recobertas com polímero conjugado poli-fenileno vinileno (PPV) forma uma opção alternativa para a fabricação de dispositivos fotovoltaicos. Os nanofios foram fabricados por Epitaxia por Feixe Molecular (MBE). Tanto potencial interno radial e modulação energética axial produzem a separação eficiente de elétrons e buracos fotoexcitados, que gera emissões de natureza e origem distintas e singulares nos nanofios: emissões envolvendo a impurezas aceitadoras no centro do núcleo de GaAs, bem como éxcitons indiretos presos a interface WZ e BZ e a interface da barreira estreita de AlGaAs na casca do nanofio. Medidas do decaimento temporal da emissão mostram uma forte dependência tempo de vida com o comprimento de onda, o que está associado com o afunilamento e distribuição energética destes estados emissivos. Medidas da emissão com a temperatura dão forte evidencia experimental de que a energia de ligação das impurezas tem uma forte dependência na direção radial. Este sistema híbrido funciona como coletor eficaz de luz tanto no visível quanto no infravermelho próximo. O trabalho demonstra também por espectroscopia resolvida no tempo que éxcitons são dissociados nas interfaces formadas por filmes ultrafinos de polímeros conjugados e nanofios e que esse material à base de arseneto de gálio (GaAs) atua como um forte receptor e separador de elétrons (alta afinidade eletrônica). / Hybrid photovoltaic devices based on conjugated polymers and inorganic semiconductors are being used in recent years to the production of solar cells at low cost. So there is a high efficiency is required efficient exciton dissociation, so it´s important to know the levels of energy of the components of the photovoltaic device. The present studies show that the hybrid system formed by cylindrical radial heterostructure nanowires prepared from alternating layers of GaAs / AlGaAs / GaAs covered with the conjugated polymer poly-phenylene vinylene (PPV) forms an alternative option for the manufacture of photovoltaic devices. Nanowires were manufactured by Molecular Beam Epitaxy (MBE). Both radial and axial inner potential energy modulation produce the efficient separation of electrons and photoexcited holes, which generates distinct and unique nature and source emissions in nanowires: emissions involving the acceptor impurities in the center core of GaAs and indirect excitons attached to the interface WZ and BZ and narrow barrier interface of AlGaAs on the shell of the nanowire. Measures the time decay of the issue show a strong dependence lifetime with the wavelength, which is associated with the bottleneck and energy distribution of emissive states. Emission measurements with temperature provide strong experimental evidence that the impurity binding energy has a strong dependence on the radial direction. This hybrid system works as an efficient collector of light both in the visible and near infrared. The work also shows for time resolved spectroscopy that excitons are dissociated at the interfaces formed by ultrathin conjugated polymers and films and nanowires that this material based on gallium arsenide (GaAs) acts as a strong receiver and electrons separator (high electron affinity ).

This thesis reports the development of a model to explain the electrical properties of Si implanted GaAs. The results show that most of the implanted silicon atoms occupy lattice sites and are electrically active. The net carrier concentration is determined by the relative concentration of silicon atoms on gallium and arsenic lattice sites respectively. The activation mechanism is shown to involve the breaking up of complex defects in the form of substitutional silicon with vacancies. The energy required for this process is about 1 to 1.5 eV. A lower value of activation energy (about 0.5 eV) has also been measured and is suggested to be associated with the site switching of silicon from arsenic to gallium sites, when a gallium vacancy diffuses close to a silicon on an arsenic site. This process has diffusion energy of about 2.5 to 3.0 eV. The activation energy obtained from sheet carrier concentration measurements corresponds to a combination of the two activation mechanisms. Which of these mechanisms is observed in an experiment depends on various parameters, such as the implantation conditions, the quality of the encapsulant and the annealing conditions. The model can explain the variations in activation energy (0.5 to 1.5 eV) reported in the literature.