A variety of benefits motivate the development of epitaxial metals, among which include the ability to design fully integrated layer structures where metallic films and nanostructures can be embedded into the cores of optoelectronic devices. Applications include high-performance tunnel-junctions, epitaxial transparent Ohmic contacts, photomixer material, and thermoelectrics. Additionally, the integration of metallic nanostructures and films into optoelectronic devices has shown potential for improving device performance and functionality through sub-wavelength confinement of plasmonic modes and enhancement of light/matter interactions. The rare-earth monopnictide (RE-V) material system can be integrated epitaxially with conventional zincblende III-V substrates under normal growth conditions, resulting in high-quality, thermodynamically stable interfaces. The RE-V semimetals span a range of optical, electrical, and structural properties, making them ideal for integration into III-V-based optoelectronic devices and applications. In this dissertation, high-quality epitaxial LuAs, LaAs and La(x)Lu(1-x)As films and nanostructures were grown and characterized for their structural, electrical, optical, and plasmonic properties. Through a sweep of alloy film compositions of the RE-V alloy material La(x)Lu(1-x)As, the ability to produce tunable epitaxial metals was demonstrated, with a range of peak transmission spectra from near- to mid-infrared wavelengths, plasmonic response in the mid-infrared, moderate resistivity, and lattice-matching potential to many relevant III-V substrates. Additionally, there is a great deal of interest in developing techniques to produce optoelectronic devices that are not restricted by substrate lattice constant. Many epitaxial approaches have been tried, with moderate success; however, growing low defect-density heteroepitaxial materials with differing crystal structures and highly-mismatched lattice parameters is extremely challenging, and such structures suffer from poor thermal properties and reliability issues. A general approach is needed for thin metamorphic buffer layers with minimal threading dislocations that simultaneously have low thermal resistance for effective heat-sinking and device reliability. An investigation was conducted into the use of RE-V nanostructure superlattices towards the reduction of dislocation density in highly-mismatched III-V systems. / text

Orientador: Maria José Santos Pompeu Brasil / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física "Gleb Wataghin" / Made available in DSpace on 2018-08-17T05:37:13Z (GMT). No. of bitstreams: 1 GonzalezBalanta_MiguelAngel_M.pdf: 3522641 bytes, checksum: 4f38baba120bb574a54a03d7c1ebc335 (MD5) Previous issue date: 2010 / Resumo: Nesta dissertação investigamos os efeitos dos íons de Mn na dinâmica do spin de elétron em poços quânticos de InGaAs/GaAs. Os poços têm um gás de buracos gerado por dopagens em suas barreiras, sendo uma dopagem tipo delta de Mn numa das barreiras e uma dopagem tipo delta de C, na outra. A densidade de buracos foi determinada mediante medidas de transporte e são consistentes com as densidades obtidas das energias de Stokeshift. Utilizamos diversas técnicas ópticas, como a fotoluminescência no modo contínuo (PL-CW) e resolvida no tempo (PL-RT), a fotoluminescência de excitação (PLE-CW), e o efeito Hanle óptico, sempre usando luz circularmente polarizada para excitação e analisando a polarização circular da luz emitida. Comparamos os tempos de vida ( ? ) e de relaxação do spin ( ? s) dos elétrons obtidos através destas técnicas e discutimos as diferenças intrínsecas destes métodos e o significado físico dos parâmetros fornecidos por eles. Analisamos também o efeito da presença dos íons de Mn, que são íons magnéticos, sobre os tempos vida e de spin dos elétrons em uma série de amostras com diferentes quantidades de Mn incluindo a amostra de referencia sem Mn. Os resultados encontrados revelam um limite para a concentração de Mn, para a qual ambos, ? e ? s, apresentam uma queda abruta. Surpreendentemente, esta queda não afeita o grau de polarização CW, pois a razão ?/? s que determina este parâmetro permanece basicamente constante para todas as amostras / Abstract: We have studied the effect of Mn ions on the spin-relaxation of electrons in a InGaAs/GaAs quantum well (QW). The QW has a two-dimensional hole-gas generated by doping the barriers, whereas one of the barriers has a Mn-planar layer and the other one, a C planarlayer. The hole densities were determined by Shubnikov-de-Haas oscillations and are consistent with the Stokes-shift energies obtained by optical measurements. We have performed continuouswave photoluminescence measurements (CW-PL), excitation photoluminescence (CW-PLE), timeresolved (TR-PL), and Hanle effect with circularly polarized excitation and detection. We compare the lifetime ( ? ) and the spin relaxation time ( ? s) obtained using those techniques and we discuss the differences between the various techniques and the physical meaning of those parameters. We also analyze the effect of Mn ions on ? s and ? for the series of samples with different Mn concentrations, including a reference sample with no Mn doping. The results revealed a threshold of Mn concentration at which both, and ? s, show a strong and abrupt fall. Surprisingly, this fall does not affect the CW effective polarization degree, since the ratio s that determines this parameter remains basically constant for all samples / Mestrado / Física da Matéria Condensada / Mestre em Física

High quality and accurate computational data was obtained through first principle quantum mechanical calculations originated from density functional theory without the inclusion of empirical data (ab initio). The support of the computing facility NGS allows us to carry out our research involving large scale atomistic simulations. The data we recently obtained clearly shows piezoelectricity in GaAs and InAs are proved to be non linear in relation to a general strain.The high order fitting equation obtained through the parameterization procedure allowed us to directly evaluate higher order piezoelectric coefficients. By comparing with other linear and non linear models and also experimental data, we reached the conclusion that the validity of our model is correct in the limitation of small shear strain, particularly in case of (111) grown semiconductors. Such limitation however is not restricted under pseudomorphic growth in (001) direction where typically shear strain is small.We further validate our model through elasticity theory to demonstrate the sign of the polarization is found to be opposite to bulk values for an InAs semiconductor layer grown in the (001) direction of growth and subject to 6-7% of lattice mismatch. This is additionally supported with experimental evidence (optical absorption spectra).Furthermore our model provides a direct way in evaluating the polarization for any crystal structure described on the atomic level. This is mainly beneficial to researchers who use molecular dynamics and empirical methods for predicting bandstructure.The fundamental performance for semiconductor devices can be improved through the use of the small polarization created from strain and is likely to bring advantages in future photovoltaics devices.

No description available.

The research carried out here employed analytical and imaging transmission electron microscopy and scanning transmission electron microscopy to gain a good understanding of local structure and composition of semiconductor nanocrystals and quantum dots for electronics and optoelectronics applications. One of the world's most advanced analytical scanning transmission electron microscopes in the field, the Daresbury SuperSTEM, was used to scrutinise the structure and composition of the samples. Three nanostructure systems are investigated in this thesis: 1. Structures consisting of Ge-nanocrystals (NCs) in alumina. Here HRTEM suggests relaxed and twinned smaller NCs grown annealed at lower temperature compared to elongated non-faulty bigger NCs annealed at higher temperature. HRTEM also suggests a polycrystalline structure of the matrix. 2. With regards to the InAs/GaAs quantum dots (QD) the study aims in particular at elucidating QD formation by investigating samples grown with and without growth interrupt (GI). Diffraction contrast TEM shows formation of buried dots in the sample prepared with GI whereas for the sample without GI the immediate growth of GaAs after InAs inhibits diffusion and segregation of In adotoms, and no footprint of buried dots has been observed. HRTEM and HAADF show coherent QDs in the sample with GI and abrupt InAs/GaAs interfaces in the sample without GI. In executing energy electron loss spectroscopy (EELS) and geometric phase analysis (GPA) the distribution of In in InGaAs/GaAs QDs has been obtained in samples grown in the critical thickness regime for quantum dot formation. The highest In percentage achieved in the dots grown with a nominal fraction of 100% was ~70%. EELS shows variations in the In concentration within the QD structure and wetting layer 3. In the case of Er-doped Si-NCs in silica this research tries to provide an understanding of structure, composition and position of excess Si and Er in the silica matrix of materials prepared under different growth conditions and to correlate this information with the PL emission, all with the aim to find preparation routes for optimum optical efficiency for applications of this materials system in silicon photonics. High spatial correlation between Si-NCs, Er and O in the Er and Si co-implanted sample with strong indication of an Er-oxide/Si core-shell structure had been found. The lack of an Er-oxide plasmon indicates, however, that the shell structure and its interface with the SiNCs is highly defective and a likely cause for non-radiative recombination. The sample with similar excess Er and Si concentrations but prepared in a two-stage implantation and annealing process shows a 10 times improvement in the optical emission. Here no spatial correlation between Er and Si-NCs was found in core loss EELS. EELS and HAADF evidenced more highly, near-atomically dispersed Er in the matrix with no formation of a core-shell structure as compared to the co-implanted sample. No footprint of Er-silicide plasmon was observed by low loss valence band EELS investigation in the co-implanted sample.

The fundamental components for processing all-optically represented data, namely optical switches and logic gates are investigated. Improved techniques for fabricating nonlinear Fabry-Perot etalons containing GaAs have brought a proliferation of GaAs optical bistable devices. These devices show significant improvements in speed, power requirements, operating temperature and thermal stability. Experiments verify predictions that one can operate a single nonlinear etalon as optical logic gates or two such etalons as a flip-flop. Optimization of the logic gates is then discussed from a systems approach.

Cette thèse s’inscrit dans le cadre d’une cotutelle internationale entre l’institut FEMTO-ST à Besançon en France et l’université de Sherbrooke au Canada. Elle porte sur l’élaboration d’un biocapteur, potentiellement à bas coût, pour la détection de pathogènes dans les secteurs de l’agroalimentaire, de l’environnement et de la biosécurité. Le modèle biologique visé est la bactérie Escherichia coli, dont les souches pathogènes sont responsables, chaque année et partout dans le monde, de plusieurs crises sanitaires liées à une mauvaise gestion des produits de consommation ou des installations de conditionnement ou de traitements de ces produits. L’utilisation de biocapteurs pour une détection rapide, sensible et sélective d’organismes pathogènes répond ainsi aux inquiétudes quant aux risques d’infection pour la population. La structure du capteur consiste en une fine membrane en arséniure de gallium (GaAs) vibrant sur des modes de cisaillement d’épaisseur générés par champ électrique latéral via les propriétés piézoélectriques du matériau. Nous montrons dans ce travail que le biocapteur offre également des possibilités de microfabrication, de biofonctionnalisation et de régénération intéressantes pour la conception d’un dispositif à bas coût. Le transducteur a été réalisé via des technologies de microfabrication utilisées en salle blanche avec une mise en parallèle des méthodes d’usinage par voie chimique et par plasma, l’objectif étant d’obtenir des membranes minces, planes et avec un état de surface de haute qualité. Une interface fluidique a été mise au point de façon à approvisionner de manière homogène le capteur en fluide. Par ailleurs, nos études se sont portées sur la fonctionnalisation biochimique de l’interface de bioreconnaissance sur l’arséniure de gallium et sa caractérisation fine par les techniques de spectroscopie infrarouge à transformée de Fourier (FTIR). Les résultats de cette étude ont permis de progresser sur la compréhension fondamentale du phénomène d’auto-assemblage de molécules sur GaAs. Un effort particulier a été mis en œuvre pour développer des biointerfaces de haute densité offrant une immobilisation optimale des immunorécepteurs biologiques. Parmi les différentes méthodes de régénération de la biointerface, le procédé de photo-oxydation UV en milieu liquide a démontré un fort potentiel pour des applications de capteurs réutilisables. Enfin, le transducteur a été caractérisé électriquement sous différents environnements. L’impact sur la réponse du résonateur des paramètres électriques, mécaniques et thermiques de ces milieux a été évalué afin de simuler le comportement du dispositif en condition réelle. / Abstract : This PhD thesis was realized in the context of a cotutelle program between FEMTO-ST institute in France and the University of Sherbrooke in Canada. The thesis addresses the development of a potentially low cost sensor dedicated for detection of pathogens in food industry processing, environment and biosafety sectors. Such a sensor could serve detection of Escherichia coli bacteria whose pathogenic strains are the source of foodborne illnesses encountered worldwide every year. Hence, biosensor devices are needed for a rapid, sensitive and selective detection of pathogens to avert, as soon as possible, any sources of contamination and prevent outbreak risks. The design of the sensor consists of a resonant membrane fabricated in gallium arsenide (GaAs) crystal that operates at shear modes of bulk acoustic waves generated by lateral field excitation. In addition to the attractive piezoelectric properties, as shown in this work, fabrication of a GaAs-based biosensor benefits from a well-developed technology of microfabrication of GaAs, as well as biofunctionalization and the possibility of regeneration that should result in cost savings of used devices. The transducer element was fabricated by using typical clean room microfabrication techniques. Plasma and wet etching were investigated and compared for achieving thin membranes with high quality surface morphology. At the same time, we designed and fabricated fluidic elements that allowed the construction of a flow cell chamber integrated in the sensor. Extensive research was carried out with a Fourier transform infrared spectroscopy (FTIR) diagnostic tool to determine optimum conditions for biofunctionalization of the GaAs surface. This activity allowed to advance the fundamental knowledge of self-assembly formation and, consequently, fabrication of high density biointerfaces for efficient immobilization of selected bioreceptors. Among different biochip regeneration methods, it has been demonstrated that liquid UV photooxidation (liquid-UVPO) has a great potential to deliver attractive surfaces for re-usable biochips. Finally, operation of the transducer device was evaluated in air environment and in various liquid media, simulating real conditions for detection.

A compact optical terahertz (THz) source was demonstrated based on an efficient high-repetition-rate doubly resonant optical parametric oscillator (OPO) around 2 mu m with two type-II phase-matched KTP crystals in the walk-off compensated configuration. The KTP OPO was intracavity pumped by an acousto-optical (AO) Q-switched Nd:YVO4 laser and emitted two tunable wavelengths near degeneracy. The tuning range extended continuously from 2.068 mu m to 2.191 mu m with a maximum output power of 3.29 W at 24 kHz, corresponding to an optical-optical conversion efficiency (from 808 nm to 2 mu m) of 20.69%. The stable pulsed dual-wavelength operation provided an ideal pump source for generating terahertz wave of micro-watt level by the difference frequency generation (DFG) method. A 7.84-mm-long periodically inverted quasi-phase-matched (QPM) GaAs crystal with 6 periods was used to generate a terahertz wave, the maximum voltage of 180 mV at 1.244 THz was acquired by a 4.2-K Si bolometer, corresponding to average output power of 0.6 mu W and DFG conversion efficiency of 4.32x10(-7). The acceptance bandwidth was found to be larger than 0.35 THz (FWHM). As to the 15-mm-long GaSe crystal used in the type-II collinear DFG, a tunable THz source ranging from 0.503 THz to 3.63 THz with the maximum output voltage of 268 mV at 1.65 THz had been achieved, and the corresponding average output power and DFG conversion efficiency were 0.9 mu W and 5.86x10(-7) respectively. This provides a potential practical palm-top tunable THz sources for portable applications.

Call number: LD2668 .T4 1986 Y36 / Master of Science / Physics

Doctor of Philosophy / Department of Chemical Engineering / James H. Edgar / The exceptional radiation resistance, high melting point, and wide energy bandgap (3.2 eV) of icosahedral boron arsenide, B[subscript]12As[subscript]2, make it an attractive candidate for applications in radiation intense environments, for example, in radioisotope batteries. These devices have potential lifetimes of decades rather than days or weeks that are typical of conventional chemical power cells. Solid state neutron detectors are another potential application of this semiconductor, as the boron-10 isotope has a high thermal neutron capture cross-section, orders of magnitude higher than most elements. To produce high quality crystalline B[subscript]12As[subscript]2 for these applications, this research focused on the epitaxy and electrical properties of B[subscript]12As[subscript]2 thin films. The major findings include the following. Twin-free heteroepitaxial B[subscript]12As[subscript]2 layers were obtained on m-plane 15R-SiC and c-plane 4H-SiC inclined 4° and 7° off-axis in the [1-100] direction. These substrates exposed asymmetric step-terrace surface structures that force B[subscript]12As[subscript]2 layers to adopt a single orientation, thus, twins were eliminated. Consequently, the crystal quality was greatly improved over films on on-axis c-plane 6H-SiC, yielding a maximum hole mobility of 80 cm[superscript]2V[superscript]-1s[superscript]-1, nearly 100 times higher than previously reported values. B[subscript]12As[subscript]2 epilayers grown at 1300°C had the lowest defect densities, smallest residual strains, highest mobility and highest deposition rate. Excess AsH[subscript]3 concentration was advantageous to prevent the loss of arsenic from the epilayer. Undoped B[subscript]12As[subscript]2 exhibited a variable-range-hopping conduction, indicating it was a highly disordered system. All films were p-type with a room temperature hole concentration on the order of 10[superscript]12~10[superscript]15cm[superscript]-3. The thermal activation energy of acceptors varied from 0.15 eV to 0.33 eV. The Hall mobility was dominated by impurity scattering at low temperatures and by polar phonon scattering at high temperatures. H, C, O and Si were the major impurities present in the undoped B[subscript]12As[subscript]2 films with concentrations on the order of 10[superscript]18~10[superscript]19 cm[superscript]-3. Si doping and annealing decreased the resistivity by up to two orders of magnitude. The density of localized states was small in the undoped B[subscript]12As[subscript]2 as the intrinsic acceptor levels (IALs) were compensated by the boron interstitials. However, in Si-doped B[subscript]12As[subscript]2, Si may prevent the interstitial boron atoms from compensating the IALs, yielding a decreased density of localized states. The Hall mobility of B[subscript]12As[subscript]2 epilayer was significantly reduced with increasing silicon concentration.