Designs for deep ultraviolet (DUV) edge emitting laser diodes (LDs) based on the wurtzite III-nitride (III-N) material system are presented. A combination of proprietary and commercial advanced semiconductor LD simulation software is used to study the operation of III-N based DUV LDs theoretically. Critical factors limiting device performance are identified based on an extensive literature survey. A comprehensive design parameter space is investigated thoroughly with the help of advanced scripting capabilities. Several design strategies are proposed to eliminate the critical problems completely or partially. A DUV LD design is proposed based exclusively on AlInN active layers grown epitaxially on bulk AlN substrates because AlInN offers a promising alternative to AlGaN for the realization of LDs and LEDs operating in the DUV regime. The proposed AlInN-based design also features a tapered electron blocking layer (EBL) instead of a homogeneous one. Tapered EBLs redistribute the interfacial polarization charge volumetrically throughout the entire EBL thickness via compositional grading, and eliminate the parasitic inversion layer charge. AlGaN based DUV LD designs are explored also because at present, it may be difficult to grow AlInN epitaxially with superior crystalline quality. Polarization charge matching is proposed to improve electron and hole wavefunction overlap within the active region. Although the strategy of polarization charge matching has already been proposed in the literature to enhance performance of visible wavelength LEDs and LDs, the proposed design presents the first demonstration that polarization charge matching is also feasible for DUV LDs operating at sub-300 nm wavelengths. A lateral current injection (LCI) LD design is proposed featuring polarization-charge-matched barriers and regrown Ohmic contacts to avoid a group of issues related to the highly inefficient p-type doping of wide bandgap III-N materials in vertical injection designs. The proposed design partially decouples the problem of electrical injection from that of optical confinement. Although the idea of an LCI LD design has been proposed in the literature in the 90s to be used as longer wavelength active sources in optoelectronic integrated circuits using GaInAsP/InP and related material systems, the proposed design is the first theoretical demonstration that this concept can be applied to DUV LDs based on III-N material system. To solve the problem of hole transport in vertical injection designs, a DUV LD design based exclusively on AlGaN material system is presented, featuring an inverse-tapered p-waveguide layer instead of an EBL. Several EBL designs are investigated, and compared with conventionally-tapered EBL design. Through judicious volumetric redistribution of fixed negative polarization charge, inverse tapering may be exploited to achieve nearly flat valence band profiles free from barriers to hole injection into the active region, in contrast to conventional designs. Numerical simulations demonstrate that the inverse tapered strategy is a viable solution for efficient hole injection in vertical injection DUV LDs operating at shorter wavelengths (< 290 nm).

Gegenstand der vorliegenden Dissertation, die am Leibniz-Institut für Festkörper- und Werkstoffforschung (IFW) in Dresden durchgeführt wurde, sind die Herstellung und Analyse von supraleitenden Dünnschichten aus Seltenerd-Nickel-Borkarbiden, die mit einer biaxialen Vorzugstextur versehen sind. Dazu wurde am Beispiel von LuNi2B2C ein Prozessfenster für epitaktisches Wachstum dieser Materialien auf MgO(110)-Einkristallsubstraten definiert, wodurch im Vergleich zu früheren Arbeiten zu Dünnschichten aus Seltenerd-Nickel-Borkarbiden eine verbesserte Textur und eine höhere Schichtqualität erzielt wurde. Struktur, insbesondere die Ausbildung der biaxialen Textur, und Supraleitung der Schichten, insbesondere die Anisotropie des oberen kritischen Feldes in Abhängigkeit von Winkel und Temperatur, bilden die beiden Schwerpunkte der Untersuchungen. Als Ausblick wurde die Abscheidung von Seltenerd-Nickel-Borkarbid-Legierungsschichten am Beispiel von (HoxLu1-x)Ni2B2C demonstriert. Durch entsprechende Anpassung der Prozessparameter konnte, von LuNi2B2C ausgehend, die biaxiale Textur in den Legierungsdünnschichten weitgehend erhalten werden. Dies schafft als Ergänzung zur Kristallzucht eine attraktive Möglichkeit für zukünftige Untersuchungen dieser Materialien.

Parmi les polytypes les plus connus du carbure de silicium (SiC), le polytype cubique (3C-SiC), est le seul qui peut croitre sur des substrats silicium. L’hétérostructure 3C-SiC/Si est intéressante non seulement pour son faible coût de production mais aussi pour la conception de Systèmes Micro-Electro-Mécaniques (« MEMS »). La valeur élevée du module de Young du 3C-SiC, comparé à celui du silicium, permettrait à des cantilevers submicroniques, fabriqués à partir de films minces de 3C-SiC, de vibrer à ultra-hautes fréquences (>100MHz). Cette haute fréquence de résonance est la clé pour obtenir un système AFM non-contact ultra-sensible et rapide. Cependant, il n’existe pas de cantilever en SiC disponible sur le marché en raison de la difficulté à élaborer des films minces de 3C-SiC de bonne qualité, la technique de synthèse la plus utilisée étant le Dépôt Chimique en phase Vapeur (CVD). La raison première de cette difficulté à obtenir un matériau de bonne qualité réside essentiellement dans l’important désaccord de maille et la différence de dilatation thermique entre le 3C-SiC et Si qui génèrent des défauts cristallins à l’interface et jusqu’à la surface du film de 3C-SiC, la zone la plus défectueuse se localisant auprès de l’interface……. / Among aIl the well known polytypes ofihe silicon carbide (SiC), the cubic polytype (3C-SiC) is the only one that min be grown on silicon substrates. This heterostructure 3C SiC/Si ta interesting not only for its low production cost but also for the design of tise Micro-Electro-Mechanical Systems (MEMS). The high value ofthe Young’s modulis the 3C-SiC, compared to the silicon, allows submicronic cantilevers, fabrmcated from tIse 3C-SiC thin filins, to resonate at ultra-high frequency (>100MHz). The high resonant frequency is the key to obtain s fast, ultra-sensitive non-contact AFM systein.However, there isn’t any SiC cantilevers available on the market because of the difficulty to elaborate gond quality 3C-SiC thin films, with tIse Chemical Vapor Deposition (CVD) technique being tIse most frequently used synthesis technology. Tise first reason of tIse difficulty with the CVD technology to obtain gond quality thin film rests essentially in the important lattice mismatch and the difference in thermal expansion coefficient existing between 3C SiC and Si which generate crystalline defects at the interface and propagating tilI the 3C-SiC filin surface, with the inost defective zone localizing near the interface…….

Group III-A nitrides (GaN, AlN, InN and alloys) are materials of considerable contemporary interest and currently enable a wide variety of optoelectronic and high-power, high-frequency electronic applications. All of these applications utilize device structures that employ a single or multiple hetero-junctions, with material compositions varying across the interface. For example, the workhorse of GaN based electronic devices is the high electron mobility transistor (HEMT) which is usually composed of an AlGaN/GaN hetero-junction, where a two-dimensional electron gas (2DEG) is formed due to differences in polarization between the two layers. In addition to such hetero-junctions in the same material family, formation of hetero-interfaces in nitrides begins right from the epitaxy of the very first layer due to the lack of native substrates for their growth. The consequences of such "dissimilar" hetero-junctions typically manifest as large defect densities at this interface which in turn gives rise to defective films. Additionally, if the substrate is also a semiconductor, the electrical properties at such dissimilar semiconductor-nitride hetero-junctions are particularly important in terms of their influence on the performance of nitride devices. Nevertheless, the large defect densities at such dissimilar 3D-3D semiconductor interfaces, which translate into more trap states, also prevents them from being used as active device layers to say nothing of reliability considerations arising because of these defects. Recently, the advent of 2D materials such as graphene and MoS2 has opened up avenues for Van der Waal’s epitaxy of these layered films with practically any other material. Such defect-free integration enables dissimilar semiconductor hetero-junctions to be used as active device layers with carrier transport across the 2D-3D hetero-interface. This thesis deals with hetero-epitaxial growth platforms for reducing defect densities, and the material and electrical properties of dissimilar hetero-junctions with the group III-A nitride material system.

This dissertation works out the vibrational properties of epitaxial silicene, which was discovered by Vogt et al. in 2012 by the epitaxial synthesis on the silver substrate. Its two-dimensional (2D) character is modified in comparison to the free-standing silicene due to its epitaxial nature, since the underlying substrate alters the physical properties of silicene as a result of the strong hybridization of the electronic levels of the substrate and adlayer. The growth of silicene layers is complicated by the sensitivity of the Si structures to the experimental conditions, mainly temperature, resulting in the formation of several seemingly different surface reconstructions. Another Si structure appears on the Ag surface at a supramonolayer coverage. The Raman spectroscopy was utilized to understand the relation between different Si structures and reveal their origin as well as to investigate the phonon-related physical properties of two-dimensional Si sheets. The central core of this work is the growth and characterization of these 2D silicene monolayers on the Ag (111) surface as well as the formation of silicene multilayer structures. The characterization of these materials was performed using in situ surface-sensitive measurement methods such as Raman spectroscopy and low-energy electron diffraction under ultra-high vacuum conditions due to high chemical reactivity of epitaxial silicene. Additional characterization was done ex situ by means of scanning force microscopy. The experimentally determined spectral signature of the prototypical epitaxial (3x3)/(4x4) silicene structure was confirmed by ab initio calculations, in collaboration with theory groups. The Raman signatures of the other 2D and 3D Si phases on Ag (111) were determined which allowed us to provide a clear picture of their formation depending on the preparation conditions. The monitoring of the silicene multi-layer growth yielded the vibrational signature of the top layer, reconstructed in a (√3x√3) fashion. It was compared to the inverse, (√3x√3)-Ag/Si(111), system showing the vast amount of similarities, which suggest that the (√3x√3) reconstruction belong to the silver layer. The chemical and physical properties of this surface structure additionally strengthen this equivalence. The possibility of functionalization of epitaxial silicene was demonstrated via exposure to the atomic hydrogen under UHV conditions. The adsorbed hydrogen covalently bonds to the silicene lattice modifying it and reducing its symmetry. As shown by Raman spectroscopy, such modification can be reversed by thermal desorption of hydrogen. The excitation-dependent Raman measurements also suggest the change of the electronic properties of epitaxial silicene upon hydrogenation suggesting that its originally semi-metallic character is modified into a semiconducting one. / Die experimentellen Forschungsarbeiten zum Thema Silicen basieren auf den 2012 von Vogt et al. durchgeführten Untersuchungen zu dessen Synthese auf Silbersubstraten. Diese Untersuchungen lieferten die Grundlage, auf der zweidimensionales (2D) epitaktisches Silicen sowie weitere 2D Materialien untersucht werden konnten. In den anfänglichen Arbeiten konnte dabei gezeigt werden, dass sich die Eigenschaften von epitaktischem Silicen gegenüber den theoretischen Vorhersagen von frei-stehendem Silicen unterscheiden. Darüber hinaus verkomplizieren sich die experimentellen Untersuchungen dieses 2D Materials, da auf dem Ag(111) Wachstumssubstrat sechs verschiedene 2D Si Polytypen existieren. Eine detaillierte Darstellung dieser Untersuchungen findet sich in dem einführenden Kapitel der vorliegen Promotionsschrift. Der zentrale Kern dieser Arbeit beschäftigt sich mit dem Wachstum und der Charakterisierung dieser 2D Silicen Monolagen auf Ag(111) Oberflächen sowie der Bildung von Silicen- Multilagen Strukturen. Die Charakterisierung dieser Materialien wurde in situ mit oberflächenempfindlichen Messmethoden wie der Raman Spektroskopie und der niederenergetischen Elektronenbeugung unter Ultrahochvakuum-Bedingungen durchgeführt. Eine zusätzliche Charakterisierung erfolgte ex situ mittels Raster-KraftMikroskopie. Die experimentell bestimmte spektrale Raman-Signatur der prototypischen epitaktischen (3x3)/(4x4) Silicene Struktur wurde durch ab initio Rechnungen, in Zusammenarbeit mit Theoriegruppen, bestätigt. Durch diesen Vergleich wir die zweidimensionale Natur der epitaktischen Silicen-Schichten vollständig bestätigt, wodurch andere mögliche Interpretationen ausgeschlossen werden können. Darüber hinaus wurden die Ramans-Signaturen der weiteren 2D und 3D Siliziumphasen auf Ag(111) bestimmt, wodurch sich ein klares Bild der Bildung dieser Strukturen in Abhängigkeit von den Präparationsbedingungen ergibt. Um die Möglichkeit der Funktionalisierung von Silicen und der weiteren 2D Si Strukturen zu testen, wurden diese unter UHV Bedingungen atomarem Wasserstoff ausgesetzt. Durch die Bindung zu den Wasserstoffamen wird die kristalline Struktur der Silicen-Schichten modifiziert und die Symmetrie reduziert, was sich deutlich in der spektralen Raman-Signatur zeigt. Wie mittels Raman Spektroskopie gezeigt werden konnte, kann diese Modifikation durch thermische Desorption des Wasserstoffs rückgängig gemacht werden, ist also reversibel. Raman Messungen mit verschiedenen Anregungswellenlängen deuten darüber hinaus auf die Änderung der elektronischen Eigenschaften der Silicen-Schichten durch die Hydrierung hin. Der ursprüngliche halbmetallische Charakter der epitaktischen Silicen-Schicht geht möglicherweise in einen halbleitenden Zustand über. Das Wachstum von Silicen Multilagen wurde ebenfalls mit in situ Ramanspektroskopie verfolgt. Die sich dabei ergebene Raman-Signatur wurde mit der Raman-Signatur von Ag terminiertem Si(111) verglichen. Hier zeigen sich große Ähnlichkeiten, die auf eine ähnliche atomare Struktur hindeuten und zeigen, dass Ag Atome für die Ausbildung der Oberflächenstruktur während des Wachstums der Si-Lagen verantwortlich sind. Die chemischen und physikalischen Eigenschaften dieser Struktur bestärken zusätzlich diese Äquivalenz.

Gegenstand der vorliegenden Dissertation, die am Leibniz-Institut für Festkörper- und Werkstoffforschung (IFW) in Dresden durchgeführt wurde, sind die Herstellung und Analyse von supraleitenden Dünnschichten aus Seltenerd-Nickel-Borkarbiden, die mit einer biaxialen Vorzugstextur versehen sind. Dazu wurde am Beispiel von LuNi2B2C ein Prozessfenster für epitaktisches Wachstum dieser Materialien auf MgO(110)-Einkristallsubstraten definiert, wodurch im Vergleich zu früheren Arbeiten zu Dünnschichten aus Seltenerd-Nickel-Borkarbiden eine verbesserte Textur und eine höhere Schichtqualität erzielt wurde. Struktur, insbesondere die Ausbildung der biaxialen Textur, und Supraleitung der Schichten, insbesondere die Anisotropie des oberen kritischen Feldes in Abhängigkeit von Winkel und Temperatur, bilden die beiden Schwerpunkte der Untersuchungen. Als Ausblick wurde die Abscheidung von Seltenerd-Nickel-Borkarbid-Legierungsschichten am Beispiel von (HoxLu1-x)Ni2B2C demonstriert. Durch entsprechende Anpassung der Prozessparameter konnte, von LuNi2B2C ausgehend, die biaxiale Textur in den Legierungsdünnschichten weitgehend erhalten werden. Dies schafft als Ergänzung zur Kristallzucht eine attraktive Möglichkeit für zukünftige Untersuchungen dieser Materialien.:Einleitung 1 Seltenerd–Nickel–Borkarbide: Materialeigenschaften und Herstellungsverfahren 2 Schichtpräparation 3 Strukturelle Eigenschaften der LuNi2B2C–Dünnschichten 4 In–Plane–Orientierung und Texturentwicklung 5 Supraleitende Eigenschaften der LuNi2B2C–Dünnschichten 6 Anisotropie des oberen kritischen Feldes in LuNi2B2C 7 Epitaktische HoxLu1-xNi2B2C–Mischserie 8 Zusammenfassung und Ausblick Anhang

The present thesis deals with the occupied and unoccupied electronic states of intermetallic compounds of the rare-earth metals (RE) Eu and Yb with the transition metals Pd and Ni. The compounds were prepared in-situ as epitaxial thin films on single-crystalline substrates. For comparison, the experiments were extended to a Ba/Pd compound, which was prepared in the same way. All samples were characterised by low-energy electron diffraction (LEED), photoelectron spectroscopy (PES) and inverse photoemission (IPE). For the IPE experiments an appropriate spectrometer was built. It consists of a combination of a toroidal-grating and a crystal monochromator and enables experiments with photon energies in the range of 10-25 eV and at 1486.6 eV. LEED experiments reveal the formation of a AuCu3 structure with a (111) surface orientation for RE/Pd systems, while the formation of a CaCu5-structure with (0001) surface orientation for the Ba/Pd and Eu/Ni compounds was found. The Eu compounds show a surface-valence transition from the trivalent to the divalent configuration. An ordered overstructure is formed at the surface despite an increase of the ionic volume of Eu by about 40 %. The measured electronic structure is in good accordance with results of local-density-approximation band-structure calculations. / In der vorliegenden Dissertation werden die besetzten und unbesetzten elektronischen Zustände intermetallischer Verbindungen der Seltenen Erden (SE) Eu und Yb mit den Übergangsmetallen Pd und Ni betrachtet. Die Verbindungen wurden als epitaktische Dünnschichten in-situ auf einkristallinen Substraten präpariert und mittels niederenergetischer Elektronenbeugung (LEED), Photoelektronenspektroskopie (PES) und inverser Photoemission (IPE) charakterisiert. Zu Vergleichszwecken wurde die Untersuchung zusätzlich auf eine auf gleiche Weise präparierte Ba/Pd-Verbindung ausgedehnt. Für die Durchführung der IPE-Experimente wurde ein entsprechendes Spektrometer aufgebaut. Die Kombination aus einem Toroidgitter- und einem Kristallmonochromator ermöglicht wahlweise Experimente im Photonenenergiebereich von 10-25 eV und bei 1486,6 eV. Die Analysen der LEED-Daten ergaben für die SE/Pd-Systeme die Bildung der AuCu3-Struktur mit einer (111)-Oberflächenorientierung, für die Ba/Pd- und die Eu/Ni-Verbindungen die der CaCu5-Struktur mit (0001)&amp;quot;=Oberflächenorientierung. Die Eu-Verbindungen zeigen dabei Oberflächenvalenzübergänge von der drei- zu der zweiwertigen Konfiguration mit Ausbildung geordneter Überstrukturen an der Oberfläche trotz einer 40 prozentigen Zunahme des Eu-Ionenvolumens. Die beobachtete elektronische Struktur stimmt gut mit den Ergebnissen von Bandstrukturrechnungen in der lokalen Dichtenäherung überein.

Microstructure and micro-mechanical characterization of as-built and heat-treated samples of Hastelloy X produced by laser powder bed fusion (LPBF) process has been carried out in this study. As-built LPBF blocks were solution heat-treated at 1177°C and 1220°C followed by fast cooling. The microstructure of as-built and heat-treated samples were studied by light optical microscopy, scanning electron microscopy, and electron backscatter diffraction. Instrumented indentation micro Vickers testing was performed to obtain microhardness and elastic modulus of asbuilt and heat-treated samples. Microtensile samples from as-built and heat-treated blocks were prepared and polished for mechanical characterization. Microtensile testing inside the scanning electron microscope was performed to evaluate the mechanical properties and to get information about the microstructural changes during plastic deformation. Microstructure characterization revealed disrupted epitaxial grain growth for the as-built samples whereas the two heated-treated Hastelloy X samples exhibited equiaxed grains with varying twin fractions. As-built Hastelloy X samples exhibited higher mean hardness than heat-treated samples. The yield strength of as-built samples reveals higher values as compared to conventional wrought Hastelloy X samples, whereas lower yield strength and higher elongation were observed for heat-treated samples as compared to as-built samples. Higher elongation and lower yield strength values were observed for the samples solution heat-treated at 1220°C compared to the solution heat-treated at 1177°C. Microstructural evaluation at different plastic strains during in-situ microtensile testing reveals a clear difference in dislocation density for as-built and heat-treated samples.

Despite enormous efforts and investments, the efficiency of InGaN-based green and yellow-green light emitters remains relatively low, and that limits progress in developing full color display, laser diodes, and bright light sources for general lighting. The low efficiency of light emitting devices in the green-to-yellow spectral range, also known as the “Green Gap”, is considered a global concern in the LED industry. The polar c-plane orientation of GaN, which is the mainstay in the LED industry, suffers from polarization-induced separation of electrons and hole wavefunctions (also known as the “quantum confined Stark effect”) and low indium incorporation efficiency that are the two main factors that contribute to the Green Gap phenomenon. One possible approach that holds promise for a new generation of green and yellow light emitting devices with higher efficiency is the deployment of nonpolar and semi-polar crystallographic orientations of GaN to eliminate or mitigate polarization fields. In theory, the use of other GaN planes for light emitters could also enhance the efficiency of indium incorporation compared to c-plane. In this thesis, I present a systematic exploration of the suitable GaN orientation for future lighting technologies. First, in order to lay the groundwork for further studies, it is important to discuss the analysis of processes limiting LED efficiency and some novel designs of active regions to overcome these limitations. Afterwards, the choice of nonpolar orientations as an alternative is discussed. For nonpolar orientation, the (1-100)-oriented (m-plane) structures on patterned Si (112) and freestanding m-GaN are studied. The semi-polar orientations having substantially reduced polarization field are found to be more promising for light-emitting diodes (LEDs) owing to high indium incorporation efficiency predicted by theoretical studies. Thus, the semi-polar orientations are given close attention as alternatives for future LED technology. One of the obstacles impeding the development of this technology is the lack of suitable substrates for high quality materials having semi-polar and nonpolar orientations. Even though the growth of free-standing GaN substrates (homoepitaxy) could produce material of reasonable quality, the native nonpolar and semi-polar substrates are very expensive and small in size. On the other hand, GaN growth of semi-polar and nonpolar orientations on inexpensive, large-size foreign substrates (heteroepitaxy), including silicon (Si) and sapphire (Al2O3), usually leads to high density of extended defects (dislocations and stacking faults). Therefore, it is imperative to explore approaches that allow the reduction of defect density in the semi-polar GaN layers grown on foreign substrates. In the presented work, I develop a cost-effective preparation technique of high performance light emitting structures (GaN-on-Si, and GaN-on-Sapphire technologies). Based on theoretical calculations predicting the maximum indium incorporation efficiency at θ ~ 62º (θ being the tilt angle of the orientation with respect to c-plane), I investigate (11-22) and (1-101) semi-polar orientations featured by θ = 58º and θ = 62º, respectively, as promising candidates for green emitters. The (11-22)-oriented GaN layers are grown on planar m-plane sapphire, while the semi-polar (1-101) GaN are grown on patterned Si (001). The in-situ epitaxial lateral overgrowth techniques using SiNx nanoporous interlayers are utilized to improve the crystal quality of the layers. The data indicates the improvement of photoluminescence intensity by a factor of 5, as well as the improvement carrier lifetime by up to 85% by employing the in-situ ELO technique. The electronic and optoelectronic properties of these nonpolar and semi-polar planes include excitonic recombination dynamics, optical anisotropy, exciton localization, indium incorporation efficiency, defect-related optical activities, and some challenges associated with these new technologies are discussed. A polarized emission from GaN quantum wells (with a degree of polarization close to 58%) with low non-radiative components is demonstrated for semi-polar (1-101) structure grown on patterned Si (001). We also demonstrated that indium incorporation efficiency is around 20% higher for the semi-polar (11-22) InGaN quantum wells compared to its c-plane counterpart. The spatially resolved cathodoluminescence spectroscopy demonstrates the uniform distribution of indium in the growth plane. The uniformity of indium is also supported by the relatively low exciton localization energy of Eloc = 7meV at 15 K for these semi-polar (11-22) InGaN quantum wells compared to several other literature reports on c-plane. The excitons are observed to undergo radiative recombination in the quantum wells in basal-plane stacking faults at room temperature. The wurtzite/zincblende electronic band-alignment of BSFs is proven to be of type II using the time-resolved differential transmission (TRDT) method. The knowledge of band alignment and degree of carrier localization in BSFs are extremely important for evaluating their effects on device properties. Future research for better understanding and potential developments of the semi-polar LEDs is pointed out at the end.

Additive Manufacturing (AM) is an innovative manufacturing process which offers near-net shape fabrication of complex components, directly from CAD models, without dies or substantial machining, resulting in a reduction in lead-time, waste, and cost. For example, the buy-to-fly ratio for a titanium component machined from forged billet is typically 10-20:1 compared to 5-7:1 when manufactured by AM. However, the production rates for most AM processes are relatively slow and AM is consequently largely of interest to the aerospace, automotive and biomedical industries. In addition, the solidification conditions in AM with the Ti alloy commonly lead to undesirable coarse columnar primary β grain structures in components. The present research is focused on developing a fundamental understanding of the influence of the processing conditions on microstructure and texture evolution and their resulting effect on the mechanical properties during additive manufacturing with a Ti6Al4V alloy, using three different techniques, namely; 1) Selective laser melting (SLM) process, 2) Electron beam selective melting (EBSM) process and, 3) Wire arc additive manufacturing (WAAM) process. The most important finding in this work was that all the AM processes produced columnar β-grain structures which grow by epitaxial re-growth up through each melted layer. By thermal modelling using TS4D (Thermal Simulation in 4 Dimensions), it has been shown that the melt pool size increased and the cooling rate decreased from SLM to EBSM and to the WAAM process. The prior β grain size also increased with melt pool size from a finer size in the SLM to a moderate size in EBSM and to huge grains in WAAM that can be seen by eye. However, despite the large difference in power density between the processes, they all had similar G/R (thermal gradient/growth rate) ratios, which were predicted to lie in the columnar growth region in the solidification diagram. The EBSM process showed a pronounced local heterogeneity in the microstructure in local transition areas, when there was a change in geometry; for e.g. change in wall thickness, thin to thick capping section, cross-over’s, V-transitions, etc. By reconstruction of the high temperature β microstructure, it has been shown that all the AM platforms showed primary columnar β grains with a <001>β.