In recent years, Silicon Photonics has emerged as a promising technology for cost-effective fabrication of photonic components and integrated circuits, the application of which is recently expanding in technological fields beyond tele- and data-communications, such as sensing and biophotonics. Compact, energy-efficient laser sources with precise wavelength control are crucial for the aforementioned applications. However, practical, efficient, electrically-pumped lasers on Silicon or other group IV elements are still absent, owing to the indirect bandgap of those materials. Consequently, the integration of III-V compounds on Silicon currently appears to be the most viable route to the realization of such lasers. In this thesis, I present and explore the potential of an External Cavity (EC) hybrid III-V/Silicon laser design, comprising a III-V-based Reflective Semiconductor Optical Amplifier (RSOA) and a Silicon reflector chip, based on a two-dimensional Photonic Crystal (PhC) cavity vertically coupled to a low-refractive-index dielectric waveguide. The vertically coupled system functions as a wavelength-selective reflector, determining the lasing wavelength. Based on this architecture mW-level continuous-wave (CW) lasing at room temperature was shown both in a fiber-based long cavity scheme and die-based short cavity scheme, with SMSR of > 25 dB and > 40 dB, respectively. Furthermore, by electrically modulating the refractive index of the PhC cavity in the reflector chip, tuning of the emitted wavelength was achieved in the die-based short cavity EC laser configuration. In this way, I demonstrated the suitability of the examined EC configuration for direct frequency modulation. The proposed scheme eliminates the need for wavelength matching between the laser source and a resonant modulator, and reveals the potential of employing low-power-consumption resonant modulation in practical Silicon Photonics applications.

IQE (Europe) Ltd. manufactures group III/V compound semiconductor material structures, using the Metal Organic Vapour Phase Epitaxy process. The manufactured ranges of semi-conducting materials are relative to discrete or multi-compound use of Gallium Arsenide or Indium Phosphide [III/V]. For MOVPE to compete in large-scale markets, the manufacturing process requires transformation into a reliable, repeatable production process. This need is identified within the process scrap percentage of the process when benchmarked against the more mature Si-CVD process. With this wide-ranging product base and different material systems, flexible processes and systems are essential. The negative impact however, of this demanded flexibility is a complex system, resulting in instability. Minor fluctuations in time, flow, pressure, temperature, or composition in the manufacturing process, will lead to characteristic differences in the produced material [product], when comparing the prescribed run to the actual run. The product profile changes very rapidly, correspondingly the failure profile of the process is equally as dynamic, it is essential therefore that the analysis and projected activities and actions can be identified and consolidated in a timely manner. This project evaluates the process used by IQEE to manufacture III/V compound semi-conducting material structures and uses the business performance to identify the process drivers. One year's [1997] business and process information is used for a single iteration of the improvement cycle. These drivers are then utilised as operators and offer the critical weaknesses in the process related to performance blockages. Some of the techniques utilised in the process evaluation and cause derivation; are original contributions specifically derived for use with a multi-platform complex process with multiple cause and effect operators. A double reporting FMEA contributes a differing rank for like machines running differing products, offering a machine specific failure profile. A novel composite of P-diagram and process flow techniques enables determination of activity influences confirming the key failure mechanism as previously identified by the business risk analysis. This project concludes by nominating the key failure mechanism accounting for 41% of the approximate 50% scrap figure identified again within the business risk analysis. The effects attributed to this failure mechanism are 2- dimensionally analysed utilising an original double operating FMEA, plotting effect to effect for the individual causes, offering a prioritised list of failure categories. The highest priority failure mode is addressed by an equipment design exercise, resulting in an overall 10% sales potential recontribution.

Made available in DSpace on 2016-06-02T20:15:24Z (GMT). No. of bitstreams: 1 4172.pdf: 7642766 bytes, checksum: 9dacbeac3b1c3b074d74029cfe1395d6 (MD5) Previous issue date: 2012-02-16 / Financiadora de Estudos e Projetos / The present work aims the study of electronic, elastic and structural properties of a whole class of nanoscopic semiconductors systems, which include quasi-two-dimensional, one-dimensional and zero-dimensional confined systems. Within two-dimensional systems, the effects caused by strain and temperature on the electronic structure of AlGaAs=GaAs multiple quantum wells oriented along [001] and [113] crystallographic directions were studied. The energy difference between light- and heavy-hole states as a function of temperature, for both crystallographic directions, was obtained from photoluminescence spectra. Using k _ p calculations, it was possible to phenomenologically explain experimental data and to show that electronic structure of quantum wells grown along [113] direction presents higher sensitivity to temperature variation. A second task in quasi-two-dimensional systems was the study of the magnetic response of neutral excitons in AlGaAs=GaAs simple quantum wells grown along [110] crystallographic direction. The Zeeman splitting and the degree of circular polarization (DCP) for the sample was extracted from circularly polarized photoluminescence spectra. Using k _ p calculations, it was possible to show that the valence band presents a high hybridization of spin states in this kind of system. To simulate the relative occupation of hybridized states, a dynamic model for spin relaxation combined with electronic structure calculations was performed. Based on theoretical results, the experimental data of the Zeeman splitting and DCP were satisfactorily and phenomenologically explained. As the last task in quasi-two-dimensional systems, the effect of in-plane magnetic field in a AlGaAs=GaAs double quantum well system was studied. As the main result, the envelope functions required for an efficient k _ p calculation in this kind of system was constructed. Concerning one-dimensional confined systems, structural properties of a twin-plane superlattice in InP nanowires were studied. The system was simulated along [111] crystallographic direction by molecular dynamics. The latter provided, besides nanowire atomic structure, stress tensor elements and elastic constants at T = 0 K. Giving the molecular dynamics results, it was possible to theoretically calculate strain tensor components and the potential profiles at the valence and conduction energy bands. The calculations showed how the strain potential profiles modulate the electronic band structure of the nanowire, generating a one-dimensional superlattice. Finally, within zero-dimensional confined systems, dynamic effects detected in the time-resolved emission from InAs quantum dots ensembles were studied. To explain the experimental behavior of the time decay as a function of quantum dots emission energy, the electron-phonon interaction, considering Fröhlich Hamiltonian model, and a carrier dynamics, that takes in account nonlinear effects such as carrier imbalance, were included in theoretically calculations. The theoretical results show that, when the system behaves like an ensemble, collective effects predominate, and different relaxation processes stand out in the system, distinguishing it from that one of isolated quantum dots. By means of theoretical calculations it was possible to satisfactorily explain the experimental data. / Este trabalho visa o estudo das propriedades eletrônicas, elásticas e estruturais de toda uma classe de sistemas semicondutores denominada de nanoscópica, a qual abrange sistemas quase bidimensionais, unidimensionais e zero-dimensionais. Nos sistemas quase bidimensionais se investigou os efeitos que o strain e a temperatura provocam na estrutura eletrônica de poços quânticos múltiplos de AlGaAs=GaAs orientados ao longo das direções cristalográficas [001] e [113]. A partir de espectros de fotoluminescência se obteve a dependência da diferença de energia entre os estados de buraco pesado e buraco leve em função da temperatura para as duas direções cristalográficas. Calculando a estrutura de bandas via método k _ p foi possível explicar fenomenologicamente os dados experimentais, e mostrar que a estrutura eletrônica do poço crescido ao longo da direção [113] é mais sensível aos efeitos da temperatura. Estudou-se também a resposta magnética de éxcitons neutros em poços quânticos simples de AlGaAs=GaAs orientados ao longo da direção cristalográfica [110]. Por meio da fotoluminescência com luz circularmente polarizada se obteve experimentalmente o desdobramento Zeeman e o grau de polarização circular (DCP). O cálculo da estrutura de bandas via k _ p mostrou que neste sistema a banda de valência se mostra altamente sensível à hibridização dos estados de spin. Para simular a ocupação relativa destes estados hibridizados combinou-se um modelo dinâmico de taxas de relaxação de spins com cálculos de estrutura eletrônica. A partir dos resultados teóricos foi possível explicar de forma satisfatória o comportamento experimental tanto do desdobramento Zeeman quanto do DCP. Ainda nos sistema bidimensionais estudou-se também o efeito da aplicação do campo magnético perpendicular à direção de quantização na estrutura eletrônica de poços quânticos duplos acoplados de AlGaAs=GaAs. Como principal resultado se obteve a função envelope, necessária para um cálculo eficiente da estrutura eletrônica via k_p neste tipo de sistema. No estudo voltado para sistemas unidimensionais foram investigadas as propriedades estruturais de uma super-rede twinning em um nanofio de InP. O sistema foi simulado ao longo da direção [111] por dinâmica molecular, que forneceu, além da estrutura atômica do nanofio, os elementos do tensor de stress e as constantes elásticas a 0 K. A partir destes resultados obteve-se teoricamente os elementos do tensor de strain e o perfil de potencial gerado pelo campo de strain. Os cálculos mostraram que estes potenciais geram uma modulação na estrutura de bandas do nanofio, criando um perfil de potencial do tipo gerado por uma super-rede unidimensional. Por fim, em sistemas zero-dimensionais se estudou os efeitos dinâmicos detectados a partir da emissão resolvida no tempo de um ensemble de pontos quânticos de InAs. Para explicar o comportamento experimental do tempo de decaimento óptico, em função da energia de emissão do sistema, foram feitos cálculos teóricos do tempo de decaimento levando-se em conta a interação elétron-fônon, por meio do Hamiltoniano de Fröhlich, e uma dinâmica de portadores, a qual inclui efeitos não lineares como o desbalanço de cargas. Os resultados mostraram que quando o sistema se apresenta como um ensemble os efeitos coletivos predominam, fazendo com que o sistema apresente propriedades diferenciadas com relação a um sistema de pontos quânticos isolados. Por meio dos cálculos teóricos foi possível explicar de maneira satisfatória os resultados experimentais.

Cette thèse porte sur l'étude des propriétés dynamiques et non linéaires des dans les semi-conducteurs Ill-V et leur utilisation pour le traitement optique dans les réseaux de télécommunication haut débit. Elle est décomposée en deux axes majeurs. Le premier est lié à l'utilisation couplée des transitions inter-bandes (18) et inter-sousbandes (188). Les différences entre ces deux types de transitions, en termes de dynamique et de sensibilité à la polarisation, font des composants 18/188 de bons candidats pour la réalisation de fonctions de traitement avancées. Dans cette optique nous avons réalisé et caractérisé un nouveau composant à puits quantiques lnGaAs/AIAs8b sur substrat lnP insérés dans une jonction pn. Les premiers résultats obtenus indiquent un comportement de diode mais révèlent que la zone de charge espace est décalée lié à un probable dopage effectif non intentionnel de I'AIAs8b. La mesure du photocourant en fonction de la polarisation électrique révèle un transport via un effet Poole-Frenkel et montre l'efficacité des barrières de potentiel AIAs8b. Ces résultats nous permettent d'envisager aussi bien des applications purement optiques (modulation de phase ou d'intensité croisées ...) qu'optoélectroniques (photo détection à deux photons). Le deuxième axe consiste à l'étude et la réalisation d'un montage permettant une caractérisation poussée de la dynamique phase/amplitude et de la réponse non linéaire de tels composants. L'approche choisie est celle d'une mesure pompe sonde employant un circuit optique analogue à un interféromètre de 8agnac offrant à la fois une grand stabilité mécanique pour une précision de mesure élevée et la possibilité d'utiliser la polarimétrie afin d'extraire les variations de gain et d'indice pour une étude plus complète des propriétés du matériau. L'utilisation d'une source laser sub-picoseconde nous permet de résoudre les phénomènes aux temps courts. Une première démonstration de la mesure de variation phase-amplitude sur un absorbeur simple (multipuits lnGaAs/lnP) autour de 1.5microns est présentée. / This PhD thesis presents the study of some dynamics and nonlinear properties of III-V semiconductors and their use for optical processing in high-speed telecommunication networks. lt is decomposed into two major axes. The first is related to the coupled use of inter-band (18) and inter-subband (IS8) transitions. The differences between these two types of transitions, in terms of dynamics and sensitivity to polarization, make 18 I IS8 components good candidates for advanced processing functions. In this context, we have realized and characterized a new device based on lnGaAs I AIAsSb quantum wells on lnP substrate inserted in a pn junction. The first results obtained indicate a behaviour of diode but reveal that the space charge region is shifted. This is linked to a probable unintentional doping of AIAsSb. The measurement of the photocurrent according to the electrical polarization reveals a transport via a PooleFrenkel effect and shows the effectiveness of the AIAsSb potential barriers. These results allow us to consider both purely optical applications (phase modulation or cross intensity ... ) and optoelectronic applications (photo-detection with two photons). The second axis consists in the study and the realization of an advanced characterization tool to measure the phase/amplitude dynamics and the non-linear responses of such components. We have used a pump-probe measurement set-up employing an optical configuration similar to a Sagnac interferometer. lt offers both a great mechanical stability for high measurement accuracy and the possibility of using polarimetric properties in order to extract variations of the optical index (gain and refractive index) for a more complete study of the properties of the material. The use of a sub-picosecond laser source allows us to solve phenomena at short times. A first demonstration of the phaseamplitude variation measurement on a single absorber (lnGaAs / lnP multiwells) around 1.5microns is presented.

The Square Kilometre Array (SKA) is known to be the most powerful radio telescope of its type. In support of its high observational power, it is estimated that thousands of antenna unit equipped with millions of LNA (low noise amplifier) will be deployed over a large area (radius>3000km). The stringent requirements for high performance and low cost LNA design bring about many challenges in terms of material growth, device fabrication and low noise circuit designs. For the past decade, the Manchester group has been wholeheartedly committed to the research and development of high performance, low cost Monolithic Microwave Integrated Circuit (MMIC) LNA with high breakdown (15V) and low noise characteristics (1.2dB to 1.5dB) for the SKA mid-frequency application (0.4GHz to 1.4GHz). The on-going optimisation of current design is hindered by the restriction of standard i-line 1µm gate lithography. The primary focus of this work is on the design and fabrication of new, submicron gate InGaAs/InAlAs/InP pHEMTs for high frequency applications and future SKA high frequency bands. The study starts with the design and fabrication of InGaAs-InAlAs pHEMT sub-100nm gate structure using E-Beam lithography. To address the problems of short channel effect and parasitic components, devices with 128nm T-gate structure, and with optimised device geometries and enhanced material growth, having fT of 162GHz and fmax of 183GHz are demonstrated, outlining the importance of device scaling for high speed operation. In addition, a gate-sinking technique using Pd/Ti/Au metallisation scheme was investigated to meet the requirement for single voltage supply in circuit design. Device with Pd-buried gate exhibits enhanced DC and RF characteristics and showed no degradation over 5 hours’ annealing at 230˚C. The implementation of this highly thermal stable Pd Schottky gate is key to improving the device’s long-term reliability at high-temperature operation. To solve the problem of low productivity in E-Beam lithography, a simple, low cost, technique termed soft reflow was introduced by utilising the principle of solvent vaporisation in a closed chamber. It provides a hybrid solution for the fabrication of submicron device using low cost i-line lithography. The integration of this new soft reflow process with the Pd-gate sinking technique has enabled the large-scale fabrication of 250nm T-gate pHEMTs, with excellent fT of 108GHz and a fmax of 119GHz and with device yields exceeding 80%. This novel soft reflow technique provides a high yield, fast throughput, solution for the fabrication of submicron gate pHEMT and other ultra-high frequency nanoscale devices.

This doctorate thesis focuses on investigating the parameter space involved in numerically modeling the bandgap engineering of a GaInP/InGaAs/Ge lattice matched multi-junction solar cell (MJSC) using InAs/InGaAs quantum dots (QDs) in the middle sub-cell. The simulation environment – TCAD Sentaurus – solves the semiconductor equations using finite element and finite difference methods throughout well-defined meshes in the device to simulate the optoelectronic behavior first for single junction solar cells and subsequently for MJSCs with and without quantum dots under concentrated illumination of up to 1000 suns’ equivalent intensity. The MJSC device models include appropriate quantum tunneling effects arising in the tunnel junctions which serve as transparent sub-cell interconnects. These tunneling models are calibrated to measurements of AlGaAs/GaAs and AlGaAs/AlGaAs tunnel junctions reaching tunneling peak current densities above 1000 A/cm^2. Self-assembled InAs/GaAs quantum dots (QDs) are treated as an effective medium through a description of appropriate generation and recombination processes. The former includes analytical expressions for the absorption coefficient that amalgamates the contributions from the quantum dot, the InAs wetting layer (WL) and the bulk states. The latter includes radiative and non-radiative lifetimes with carrier capture and escape considerations from the confinement potentials of the QDs. The simulated external quantum efficiency was calibrated to a commercial device from Cyrium Technologies Inc., and required 130 layers of the QD effective medium to match the contribution from the QD ground state. The current – voltage simulations under standard testing conditions (1 kW/cm^2, T=298 K) demonstrated an efficiency of 29.1%, an absolute drop of 1.5% over a control structure. Although a 5% relative increase in photocurrent was observed, a 5% relative drop in open circuit voltage and an absolute drop of 3.4% in fill factor resulted from integrating lower bandgap nanostructures with shorter minority carrier lifetimes. However, these results are considered a worst case scenario since maximum capture and minimum escape rates are assumed for the effective medium model. Decreasing the band offsets demonstrated an absolute boost in efficiency of 0.5% over a control structure, thus outlining the potential benefits of using nanostructures in bandgap engineering MJSCs.

abstract: III-V-bismide semiconductor alloys are a class of materials with applications in the mid and long wave infrared spectrum. The quaternary alloy InAsSbBi is attractive because it can be grown lattice-matched to commercially available GaSb substrates, and the adjustment of the Bi and Sb mole fractions enables both lattice constant and bandgap to be tuned independently. This dissertation provides a comprehensive study of the surface morphology and the structural and chemical properties of InAsSbBi alloys grown by molecular beam epitaxy. 210 nm thick InAsSbBi layers grown at temperatures from 280 °C to 430 °C on (100) on-axis, (100) offcut 1° to (011), and (100) offcut 4° to (111)A GaSb substrates are investigated using Rutherford back scattering, X-ray diffraction, transmission electron microscopy, Nomarski optical microscopy, atomic force microscopy, and photoluminescence spectroscopy. The results indicate that the layers are coherently strained and contain dilute Bi mole fractions. Large surface droplets with diameters and densities on the order of 3 µm and 106 cm-2 are observed when the growth is performed with As overpressures around 1%. Preferential orientation of the droplets occurs along the [011 ̅] step edges offcut (100) 1° to (011) substrate. The surface droplets are not observed when the As overpressure is increased to 4%. Small crystalline droplets with diameters and densities on the order of 70 nm and 1010 cm-2 are observed between the large droplets for the growth at 430°C. Analysis of one of the small droplets indicates a misoriented zinc blende structure composed of In, Sb, and Bi, with a 6.543 ± 0.038 Å lattice constant. Lateral variation in the Bi mole fraction is observed in InAsSbBi grown at high temperature (400 °C, 420 °C) on (100) on-axis and (100) offcut 4° to (111)A substrates, but is not observed for growth at 280 °C or on (100) substrates that are offcut 1° to (011). Improved crystal and optical quality is observed in the high temperature grown InAsSbBi and CuPtB type atomic ordering on the {111}B planes is observed in the low temperature grown InAsSbBi. Strain induced tilt is observed in coherently strained InAsSbBi grown on offcut substrates. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2020

Manganese (Mn) doped III-V dilute ferromagnetic semiconductors (DFSs) are a candidate materials for semiconductor spintronics due to their intrinsic ferromagnetism mediated by holes. In this thesis, Mn doped III-V dilute ferromagnetic semiconductors (DFSs), including (Ga,Mn)As, (In,Mn)As, (Ga,Mn)P, and (In,Ga,Mn)As have been successfully prepared by ion implantation and pulsed laser melting. All (In,Ga,Mn)As films are confirmed to be well recrystallized and ferromagnetic while their Curie temperatures depend on the Ga concentration. (Ga,Mn)As and (Ga,Mn)P have an inplane easy axis, while an out-of-plane easy axis for (In,Mn)As is observed. However, all of them do not present strong in-plane uniaxial anisotropy between [110] and [110] directions, which always occurs in low temperature molecular beam epitaxy (LT-MBE) grown (Ga,Mn)As samples. The reason is ascribed to the fact that the ultra-fastrecrystallization induced by pulsed laser melting weakens the formation of Mn-Mn dimers along the [100] direction which occurs in LT-MBE grown (Ga,Mn)As. Then selected samples were co-doped with Zn or irradiated with He ions. The Zn co-doping leads to the increase of conductivity of (Ga,Mn)P, however both the Curie temperature and magnetization decrease, which is probably due to the suppression of active Mn substitution by Zn co-doping. By using Rutherford Backscattering Spectroscopy and Particle-Induced X-ray Emission, the substitutional Mn atoms in (Ga,Mn)As are observed to shift to interstitial sites, while more Zn atoms occupy Ga sites. This is consistent with first-principles calculations, showing that the formation energy of substitutional Zn and interstitial Mn is 0.7 eV lower than that of interstitial Zn and substitutional Mn. For ion irradiated (Ga,Mn)As, (In,Mn)As and (Ga,Mn)P, both Curie temperature and magnetization decrease due to the hole compensation. However, the compensation effect is the strongest in (In,Mn)As and the least in (Ga,Mn)P. This is due to the different energy level of the produced defect relative to the band edges in different semiconductors. The results in the thesis point to an important issue: the difference in the band alignment and the hole binding energy of Mn dopants in different III-Mn-V dilute ferromagnetic semiconductors have strong influence on their magnetic properties and should be taken into account in the material design.

We present a comprehensive investigation of the low-¯eld hole mobility in strained Ge and III-V (GaAs, GaSb, InSb and In1¡xGaxAs) p-channel inversion layers with both SiO2 and high-· insulators. The valence (sub)band structure of Ge and III-V channels, relaxed and under strain (tensile and compressive) is calculated using an effcient self-consistent method based on the six-band k ¢ p perturbation theory. The hole mobility is then computed using the Kubo-Greenwood formalism accounting for non-polar hole-phonon scattering (acoustic and optical), surface roughness scatter- ing, polar phonon scattering (III-Vs only), alloy scattering (alloys only) and remote phonon scattering, accounting for multi-subband dielectric screening. As expected, we find that Ge and III-V semiconductors exhibit a mobility significantly larger than the \universal" Si mobility. This is true for MOS systems with either SiO2 or high-k insulators, although the latter ones are found to degrade the hole mobility compared to SiO2 due to scattering with interfacial optical phonons. In addition, III-Vs are more sensitive to the interfacial optical phonons than Ge due to the existence of the substrate polar phonons. Strain { especially biaxial tensile stress for Ge and biaxial compressive stress for III-Vs (except for GaAs) { is found to have a significant beneficial effect with both SiO2 and HfO2. Among strained p-channels, we find a large enhancement (up to a factor of 10 with respect to Si) of the mobility in the case of uniaxial compressive stress added on a Ge p-channel similarly to the well-known case of Si. InSb exhibits the largest mobility enhancement. In0:7Ga0:3As also exhibits an increased hole mobility compared to Si, although the enhancement is not as large. Finally, our theoretical results are favorably compared with available experimental data for a relaxed Ge p-channel with a HfO2 insulator.

No description available.