Die Arbeit befasst sich mit der Untersuchung von weitbandlückigen Halbleitern über raumladungszonenspektroskopische Methoden. Dabei liegt der Schwerpunkt auf der Detektion von elektronisch und optisch aktiven Defektzuständen in solchen Materialien. Die Experimente wurden exemplarisch an dem II-VI Halbleiter Zinkoxid (ZnO) durchgeführt, welcher inform von Volumenkristallen, Mikronadeln und Dünnfilmen zur Verfügung stand. Raumladungszonen wurden über Schottky-Kontakte realisiert. Nach einer Einführung in die Theorie der Raumladungszonenspektroskopie wird ein Überblick über Defekte in verschiedenartig gezüchteten ZnO gegeben. Dazu werden die Standardverfahren Strom-Spannungs-Messung, Kapazitäts-Spannungs-Messung, Thermische Admittanz- Spektroskopie (TAS) und Deep Level Transient Spectroscopy (DLTS) verwendet. Ergänzend wurden die auf weitbandlückige Halbleiter ausgelegten Verfahren Low Rate Deep Level Transient Spectroscopy (LR-DLTS) und Deep Level Optical Spectroscopy (DLOS) eingesetzt, mit welchen es möglich ist Defektzustände in der gesamten Bandlücke von ZnO nachzuweisen. Für die untersuchten Störstellenniveaus konnten somit die thermische Aktivierungsenergie, Einfangquerschnitte freier Ladungsträger und Photoionisationsquerschnitte bestimmt werden. Typischerweise werden tiefe Defekte durch die Bestrahlung mit hochenergetischen Protonen erzeugt. Derartige Behandlungen wurden an binären ZnO- und ternären (Mg,Zn)ODünnfilmen durchgeführt, wobei die Generationsrate eines Defektes über Variation der verwendeten Strahlungsdosis bestimmt wurde. Ionenimplantationen spielen eine große Rolle im Herstellungsprozess von Bauelementen, sind jedoch für ZnO nicht etabliert. Die Auswirkung der Implantation von inerten Argon-Ionen, sowie die nachträgliche thermische Behandlung auf die Konzentration intrinsischer Defekte wurde untersucht. Zink- und Sauerstoff-Implantationen bewirken, neben der Generation von Defekten, eine lokale Änderung der Stöchiometrie. Durch einen Vergleich der Defektkonzentrationen nach Zn-, O-, Ne- und Ar-Implantation können Rückschlüsse auf die chemische Natur intrinsischer Defekte geschlossen werden.

Die Arbeit beschäftigt sich mit der Erzeugung und den Eigenschaften strahlungsinduzierter Defekte in Silizium. Zur Erzeugung der untersuchten Zentren werden Wasserstoff- und Helium-Ionenstrahlen im MeV-Bereich verwendet. Die Untersuchung erfolgt mittels Spreading-Resistance- und temperaturabhängiger Hall-Messungen. Betrachtet wird zunächst die Erzeugung einer n-Dotierung durch Wasserstoff-Implantation in Abhängigkeit von Implantationsparametern, - bedingungen und dem Ausheilprozess. Für Helium-bestrahltes Silizium werden die Auswirkungen der Bestrahlung auf Widerstand, Ladungsträgerkonzentration und Beweglichkeit untersucht.

Made available in DSpace on 2014-06-11T19:35:46Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-07-31Bitstream added on 2014-06-13T20:07:27Z : No. of bitstreams: 1 rangel_rcc_dr_bauru.pdf: 1294713 bytes, checksum: 2985112be0b4359c31e145843a70f7a7 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Neste trabalho a técnica de Implantação Iônica e Deposição por Imersão em Plasma, IIDIP, foi utilizada para deposição de filmes contendo cálcio sobre a superfície de titânio. Os parâmetros de deposição foram variados buscando-se condições que tornassem o titânio o mais bioativo possível. Para a deposição dos filmes contendo cálcio foram utilizados, como precursores, vapor de nitrato de cálcio dissolvido em álcool isopropílico ou cálcio granulado. Para avaliar a bioatividade dos filmes as amostras foram imersas em solução corpórea simulada, SBF. Espectrometria de emissão de raios X induzida por partículas carregadas (PIXE), espectroscopia de reflexão/absorção no infravermelho(IRRAS), espectroscopia de fotoelétrons de raios-x (XPS), difração de raios X (DRX) e espectroscopia de energia dispersiva (EDS) foram utilizadas para análises da composição química e estrutura molecular dos filmes depositados. A morfologia da superfície foi avaliada por microscopia eletrônica de varredura (MEV) e microscopia de força atômica (AFM). A espessura dos filmes foi medida por perfilometria, enquanto a energia de superfície e ângulo de contato foram obtidos pelo método da gota séssil em um goniômetro automatizado. Células osteoblásticas foram semeadas sobre amostras de titânio recobertas com o filme a plasma e controle e cultivadas para investigação da adesão e viabilidade celulares. Espectroscopia de impedância eletroquímica foi utilizada para avaliar modificações algumas amostras de titânio após a deposição a plasma e a imersão em SBF. Os resultados mostraram melhora na bioatividade do material, sendo que a viabilidade de células osteoblásticas aumentou mais de 100% para uma amostra de titânio tratada por IIDIP a partir de vapor da solução de nitrato de cálcio. Esse aumento na viabilidade foi atribuído a elevados... (Resumo completo, clicar acesso eletrônico / In this work Plasma Immersion Ion Implantation and Deposition, PIID, technique was employed for deposition of calcium-containing films on titanium surfaces. The deposition parameters have been varied in search of conditions that would enhance the bioactivity of titanium surfaces as much as possible. Vapor of solution of calcium nitrate dissolved in isopropyl alcohol, or the sublimation of granulated metalic calcium were used as Ca precursors. The superficial modifications were investigated before and after soaking the samples in SBF. Particle-induced x-ray emission (PIXE), infrared reflectance/absorbance (IRRAS), x-ray photoelectron (XPS), x-ray difraction (XRD) and energy-dispersive x-ray (EDS) spectroscopies were used to characterize the chemical composition and molecular structure of the films. The surface morphology was evaluated by scanning electron microscopy (MEV) and atomic force microscopy (AFM). The thickness of the films was measurement by profilometry, while the surface energy and contact angle were assessed using the sessible drop method in an automated goniometer. Osteoblast cells was seeded on the coated titanium and controls and cultured to investigate cell adhesion and viability. Electrochemical Impedance Spectroscopy, EIS, was used to evaluate changes after plasma deposition and soaking in SBF. Osteoblast cells viability increased 100% in a titanium sample treated by PIIID from vapor of calcium nitrate solution. The increasing in cell viability has been ascribed to high values of roughness and surface energy. Calcium and phosphorous were detected in samples treated by PIIID from granulated calcium after soaking in SBF. Micrographs of those surfaces have revealed morphologies typical of apatite, which presence has been confirmed by XPS and XRD. High resolution XPS spectra... (Complete abstract click electronic access below)

Ce travail porte sur l’étude des phénomènes induits par implantation d’hydrogène et/ou d’hélium dans le silicium monocristallin. Le cloquage et l’exfoliation dus à la coimplantation d’hélium et d’hydrogène ont été étudiés en fonction des paramètres d’implantation (énergie, fluence, courant, rapport H/He) et des conditions de recuit. Un comportement de type fenêtre à été observé dont le maximum de surface exfoliée dépend uniquement de la fluence. Deux mécanismes d’exfoliation liés aux régimes de fluence ont été identifiés et discutés. D’autre part, la microstructure des échantillons a été étudié par MET, et les déformations ont été mesurées par diffraction des Rayons X. Un modèle décrivant la distribution des contraintes dans le substrat implanté a été proposé. Le phénomène de delamination des substrats qui apparaît pour des conditions particulières d’implantation a également été étudié, comparé aux phénomènes de cloquage et exfoliation, et expliqué en utilisant des concepts de la mécanique de la fracture. Enfin, l’interaction élastique entre précipités d’He et d’H a été étudiée pour des profils d’implantation superposés et décalés. Dans ce dernier cas, nous avons montré que le champ de contraintes générées par les plaquettes d’hélium en surpression pouvait être utilisé comme source locale de contraintes pour contrôler la formation et la croissance de plaquettes d’hydrogène. Afin d’interpréter nos résultats expérimentaux, nous avons développé un modèle basé sur l’interaction élastique pour la nucléation des précipités dans un solide semi-infini. / The present work relates an investigation of H2 + and He+ coimplanted (001)-Si substrates. The phenomena of blistering and exfoliation were studied by SEM as a function of the implantation parameters (energy, fluence, current and H/He ration) and annealing protocol. A window behavior as function of the implanted fluence was observed and two distinct fluence dependents mechanisms of exfoliation were indentified and discussed. The microstructure of the implanted samples was studied using TEM and related to ballistic effects and stress-strain dependent interactions. The strain was measured using DRX and a model to describe the stress-strain distribution into the implanted layer is developed. A new phenomenon of delamination of thin layer from implanted Si substrates was observed to emerge from particular implantation conditions. The behavior was studied and explained using fracture mechanics concepts and contrasted to blistering/exfoliation processes. Finally, the elastic interaction between He and H plate-like precipitates giving rise to arranged nanostructure was demonstrated and studied using TEM. An elasticity based model was developed to understand the behavior. The result set the basis for further developments of nanostructures within a crystalline matrix by manipulating preferential orientations of precipitates in nanometric scale.

Title: Magnetic nanostructures for recording and optical sensors Author: Eva Lišková Department: Institute of Physics, Charles University Supervisor: Prof. Ing. Štefan Višňovský, DrSc. Abstract: Magneto-optical (MO) spectra of multilayered structures with enhanced MO effect were studied using the polar and longitudinal Kerr spectroscopy with oblique angle of light incidence in the photon energy range 1.2 eV to 5 eV. The samples with Fabry- Perot cavity like architecture, were modeled using Yeh matrix formalism. Two sets of samples, with composition FeF2/Fe/FeF2 and AlN/Fe/AlN, were prepared by molecular beam epitaxy and sputtering. The relations were studied between the position of the enhanced peak in the MO spectra and the structure. Second part of this work was devoted to the Pt/Co/Pt structures and the influence of the ion implantation on MO spectra and structural composition. The studied multilayer structures present interest for MO sensor and memory applications. Keywords: Magneto-optical Kerr effect, Magneto-optical sensor, Fabry-Perot resonator, Ion implantation

Ce travail porte sur le développement d’une technique de structuration de surface pour le silicium. Celle-ci repose sur trois étapes essentielles : la lithographie, l’implantation ionique et le retrait par voie humide. Le motif formé par lithographie est transféré par homothétie dans la couche sous-jacente de silicium grâce à l’implantation ionique. Après le retrait du masque de résine, le substrat est traité par voie humide en vue de retirer des zones localement implantées. Le motif initial défini par la lithographie est ainsi révélé dans le silicium.La compréhension des modifications induites par l’implantation ionique dans le substrat nous a permis de réaliser avec succès un transfert dans le silicium. Nous avons principalement étudié les défauts générés par deux types d’ions : l’argon et l’hydrogène, à travers un certain nombre de techniques de caractérisation. Sur la base de cette étude, les différents traitements humides du silicium ont été investigués : gravure alcaline, gravure acide, dissolution par anodisation. L’optimisation des conditions d’implantation et des paramètres de retrait humide a permis l’obtention de structures 2D puis 3D.La faisabilité de cette technique de structuration a également été démontrée sur d’autres matériaux comme le SiOCH et le nitrure de silicium. / This thesis deals with the development of a patterning process for silicon substrates. Based on ion implantation through a resist pattern to locally modified the underneath layer. Wet etching processes have been developed to reveal the shapes transferred into the silicon substrate. Thanks to morphological, physical and chemical characterizations, modifications induced by ion implantation have been identified and understood.Two ion species (argon and hydrogen) were used in this thesis in order to assess either physical or chemical modifications in silicon substrate. Several wet chemistries: alkaline, acid and dissolution by anodization, were investigated to reveal the final shape. The optimization of the implantation and wet etching processes allowed to obtain 2D and 3D structures with silicon substrate.Moreover, our approach has been successfully implemented to pattern 2D shapes in SiOCH and silicon nitride.

Orientador: Nilson Cristino da Cruz / Banca: Eliana Aparecida de Rezende Duek / Banca: Ana Paula Rosifini Alves Claro / Banca: Cecilia Amelia de Carvalho Zavaglia / Banca: Clodomiro Alves Junior / Resumo: Neste trabalho a técnica de Implantação Iônica e Deposição por Imersão em Plasma, IIDIP, foi utilizada para deposição de filmes contendo cálcio sobre a superfície de titânio. Os parâmetros de deposição foram variados buscando-se condições que tornassem o titânio o mais bioativo possível. Para a deposição dos filmes contendo cálcio foram utilizados, como precursores, vapor de nitrato de cálcio dissolvido em álcool isopropílico ou cálcio granulado. Para avaliar a bioatividade dos filmes as amostras foram imersas em solução corpórea simulada, SBF. Espectrometria de emissão de raios X induzida por partículas carregadas (PIXE), espectroscopia de reflexão/absorção no infravermelho(IRRAS), espectroscopia de fotoelétrons de raios-x (XPS), difração de raios X (DRX) e espectroscopia de energia dispersiva (EDS) foram utilizadas para análises da composição química e estrutura molecular dos filmes depositados. A morfologia da superfície foi avaliada por microscopia eletrônica de varredura (MEV) e microscopia de força atômica (AFM). A espessura dos filmes foi medida por perfilometria, enquanto a energia de superfície e ângulo de contato foram obtidos pelo método da gota séssil em um goniômetro automatizado. Células osteoblásticas foram semeadas sobre amostras de titânio recobertas com o filme a plasma e controle e cultivadas para investigação da adesão e viabilidade celulares. Espectroscopia de impedância eletroquímica foi utilizada para avaliar modificações algumas amostras de titânio após a deposição a plasma e a imersão em SBF. Os resultados mostraram melhora na bioatividade do material, sendo que a viabilidade de células osteoblásticas aumentou mais de 100% para uma amostra de titânio tratada por IIDIP a partir de vapor da solução de nitrato de cálcio. Esse aumento na viabilidade foi atribuído a elevados... (Resumo completo, clicar acesso eletrônico / Abstract: In this work Plasma Immersion Ion Implantation and Deposition, PIID, technique was employed for deposition of calcium-containing films on titanium surfaces. The deposition parameters have been varied in search of conditions that would enhance the bioactivity of titanium surfaces as much as possible. Vapor of solution of calcium nitrate dissolved in isopropyl alcohol, or the sublimation of granulated metalic calcium were used as Ca precursors. The superficial modifications were investigated before and after soaking the samples in SBF. Particle-induced x-ray emission (PIXE), infrared reflectance/absorbance (IRRAS), x-ray photoelectron (XPS), x-ray difraction (XRD) and energy-dispersive x-ray (EDS) spectroscopies were used to characterize the chemical composition and molecular structure of the films. The surface morphology was evaluated by scanning electron microscopy (MEV) and atomic force microscopy (AFM). The thickness of the films was measurement by profilometry, while the surface energy and contact angle were assessed using the sessible drop method in an automated goniometer. Osteoblast cells was seeded on the coated titanium and controls and cultured to investigate cell adhesion and viability. Electrochemical Impedance Spectroscopy, EIS, was used to evaluate changes after plasma deposition and soaking in SBF. Osteoblast cells viability increased 100% in a titanium sample treated by PIIID from vapor of calcium nitrate solution. The increasing in cell viability has been ascribed to high values of roughness and surface energy. Calcium and phosphorous were detected in samples treated by PIIID from granulated calcium after soaking in SBF. Micrographs of those surfaces have revealed morphologies typical of apatite, which presence has been confirmed by XPS and XRD. High resolution XPS spectra... (Complete abstract click electronic access below) / Doutor

Ce travail porte sur l’étude des phénomènes induits par implantation d’hydrogène et/ou d’hélium dans le silicium monocristallin. Le cloquage et l’exfoliation dus à la coimplantation d’hélium et d’hydrogène ont été étudiés en fonction des paramètres d’implantation (énergie, fluence, courant, rapport H/He) et des conditions de recuit. Un comportement de type fenêtre à été observé dont le maximum de surface exfoliée dépend uniquement de la fluence. Deux mécanismes d’exfoliation liés aux régimes de fluence ont été identifiés et discutés. D’autre part, la microstructure des échantillons a été étudié par MET, et les déformations ont été mesurées par diffraction des Rayons X. Un modèle décrivant la distribution des contraintes dans le substrat implanté a été proposé. Le phénomène de delamination des substrats qui apparaît pour des conditions particulières d’implantation a également été étudié, comparé aux phénomènes de cloquage et exfoliation, et expliqué en utilisant des concepts de la mécanique de la fracture. Enfin, l’interaction élastique entre précipités d’He et d’H a été étudiée pour des profils d’implantation superposés et décalés. Dans ce dernier cas, nous avons montré que le champ de contraintes générées par les plaquettes d’hélium en surpression pouvait être utilisé comme source locale de contraintes pour contrôler la formation et la croissance de plaquettes d’hydrogène. Afin d’interpréter nos résultats expérimentaux, nous avons développé un modèle basé sur l’interaction élastique pour la nucléation des précipités dans un solide semi-infini. / The present work relates an investigation of H2 + and He+ coimplanted (001)-Si substrates. The phenomena of blistering and exfoliation were studied by SEM as a function of the implantation parameters (energy, fluence, current and H/He ration) and annealing protocol. A window behavior as function of the implanted fluence was observed and two distinct fluence dependents mechanisms of exfoliation were indentified and discussed. The microstructure of the implanted samples was studied using TEM and related to ballistic effects and stress-strain dependent interactions. The strain was measured using DRX and a model to describe the stress-strain distribution into the implanted layer is developed. A new phenomenon of delamination of thin layer from implanted Si substrates was observed to emerge from particular implantation conditions. The behavior was studied and explained using fracture mechanics concepts and contrasted to blistering/exfoliation processes. Finally, the elastic interaction between He and H plate-like precipitates giving rise to arranged nanostructure was demonstrated and studied using TEM. An elasticity based model was developed to understand the behavior. The result set the basis for further developments of nanostructures within a crystalline matrix by manipulating preferential orientations of precipitates in nanometric scale.

Les convertisseurs à base de Si atteignent leurs limites. Face à ces besoins, le GaN, avec sa vitesse de saturation des électrons et le champ électrique de claquage élevés est candidat idéal pour réaliser des redresseurs, surtout s’il est épitaxié sur substrat à bas cout. Ce travail est dédié au développement des diodes Schottky sur AlGaN/GaN. Une couche de SiNx en faible traction a été obtenue. Un contact ohmique de Ti/Al avec une gravure partiel a donné une Rc de 2.8 Ω.mm avec une résistance Rsh de 480 Ω/□. Des diodes Schottky avec les étapes issues de ces études ont été fabriqué. La diode recuite à 400 °C avec 30 nm de profondeur de gravure a montré une hauteur de barrière de 0,82 eV et un facteur d'idéalité de 1,49. La diode a présenté une très faible densité de courant de fuite de 8.45x10-8 A.mm-1 à -400 V avec une tension de claquage entre 480 V et 750 V. / Si-based devices for power conversion applications are reaching their limits. Wide band gap GaN is particularly interesting due to the high electron saturation velocity and high breakdown electric field, especially when epitaxied on low cost substrates such as Si. This work was dedicated to the development and fabrication of the Schottky diode on AlGaN/GaN on Si. SiNx passivation in very low tensile strain is used. Ti (70 nm)/Al (180 nm) partially recessed ohmic contacts annealed at 800 ºC exhibited a 2.8 Ω.mm Rc with a sheet resistance of 480 Ω/sq. Schottky diodes with the previously cited passivation and ohmic contact were fabricated with a fully recessed Schottky contact annealed at 400 ºC. A Schottky barrier height of 0.82 eV and an ideality factor of 1.49 were obtained. These diodes also exhibited a very low leakage current density (up to -400 V) of 8.45x10-8 A.mm-1. The breakdown voltage varied between 480 V and 750 V.

O Nitreto de Gálio (GaN) é um semicondutor de gap direto, motivo de numerosas pesquisas científicas, principalmente devido a sua importância na fabricação de dispositivos de alta potência e optoeletrônicas. Ligas de GaN como InGaN e AlGaN, por exemplo, possibilitam a fabricação de LEDs e LASERs azuis. Neste nosso estudo selecionamos o Arseneto de Gálio (GaAs) como um substrato viável para síntese de GaN mediante a permuta de Arsênio (As) por Nitrogênio (N) fundamentada em três passos: a) incorporação de N por implantação iônica em GaAs (à 350, 450 ou 550 ºC) em elevadas fluências (1, 2, 3 ou 4 × 1017 N/cm2); b) maior estabilidade das ligações Ga-N frente às de Ga-As; e c) expurgo de As da região contendo N implantado mediante recozimentos (à 550, 650, 750, 850 ou 1000 ºC) sob fluxo de N2. Uma capa de ~ 125 nm de Nitreto de Silício (Si3N4) foi depositada por sputtering sobre o GaAs previamente a implantação à quente: camada de sacrifício que pode ser removida após a síntese. Análises por Microscopia Eletrônica de Transmissão (TEM) e Espectroscopia de Raios- X por Dispersão em Energia (EDS) demonstraram que, no estado como-implantado da fluência de 3 × 1017 N/cm2, formam-se bolhas de N para ambos os lados da interface Si3N4/GaAs e a região implantada do GaAs amorfiza. Após um recozimento à 850 ºC/5 min, observou-se uma elevada degradação da camada de Si3N4, fragilizada pela formação das bolhas de N. Formou-se uma camada contínua de GaN (GaN-layer) de ~ 70 nm na sua fase hexagonal, sustentada por “pilares” no substrato GaAs, entre os quais existem extensos vazios. Medidas TEM em alta resolução (HRTEM) e por Difração de Elétrons de Área Selecionada (SAED) revelaram que a GaN-layer apresenta forte tendência à epitaxia com o substrato GaAs (relações de epitaxia são aqui apresentadas), e regiões estruturalmente espelhadas (i.e., twins). SAED sobre os pilares evidenciaram uma fase transicional cúbica, com um parâmetro de rede substancialmente menor (0,42 ± 0,01) nm que o reportado na literatura (0,45 nm). Estudos por Espectrometria de Retroespalhamento de Rutherford e Canalização (RBS/C) mostraram que a GaN-layer é rica em N (Ga1,00N1,90, para 3 × 1017 N/cm2) e apresenta canalização (para implantações de 2 e 3 × 1017 N/cm2), confirmando o caráter monocristalino identificado por TEM. Medidas de Fotoluminescência (PL) confirmam emissão na região do gap de banda do α-GaN (~ 3,4 eV), bem como bandas associadas a defeitos estruturais do material. Também foi investigado o efeito de campos de tensão provenientes de bolhas de Hélio (He) mediante a realização da síntese a partir de substrato GaAs pré-implantado com He. Neste caso, as bolhas, que se formam no GaAs durante a implantação de N à quente e extinguem-se após recozimentos, limitam a difusão de N para o interior do substrato, conduzindo a formação de uma GaN-layer mais espessa (~ 120 nm) e com bem mais N (Ga1,00N2,80). Como consequência, a GaNlayer apresentou um caráter mais policristalino. / The Gallium Nitride (GaN) is a direct gap semiconductor, is issue of numerous scientific research, mainly due to its importance in the manufacture of high power devices and optoelectronic devices. GaN alloys, as InGaN and AlGaN, for example, enable the production of LEDs and blue LASERs. In this study, we have selected Gallium Arsenide (GaAs) as a suitable substrate for GaN synthesis through Arsenic (As) replacement by Nitrogen (N), based on three steps: a) incorporation of N by ion implantation into GaAs (at 350, 450 or 550 ºC) at high fluences (1, 2, 3 or 4 × 1017 N/cm2); b) higher stability of the Ga-N bonds compared to the Ga-As ones; and c) purge of As from the region containing implanted N by annealing (at 550, 650, 750, 850 or 1000 ºC) under N2 flow. A 125-nm cap-layer of Silicon Nitride (Si3N4) was deposited by sputtering on GaAs prior to the hot implantation: it is a sacrifice layer which can be removed after the synthesis. Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectroscopy (EDS) analyzes demonstrated that, on the as-implanted state of the fluence of 3 × 1017 N/cm2, N bubbles are formed on both sides of the Si3N4/GaAs interface and the implanted region of GaAs amorphizes. After annealing at 850 °C/5min, a high degradation of the Si3N4 layer was observed, weakened by the formation of N bubbles. A continuous layer of GaN (GaN-layer) of ~ 70 nm was formed in its hexagonal phase, supported by “pillars” on the GaAs substrate, with extensive voids in between them. High-Resolution TEM (HRTEM) and Selected Area Electron Diffraction (SAED) measurements revealed that the GaN-layer exhibits a strong tendency to epitaxy with the GaAs substrate (epitaxial relationships are here presented), and structurally mirrored regions (i.e., twins). SAED on the pillars showed a transitional cubic phase, with a lattice parameter substantially smaller (0.42 ± 0.01) nm than the one reported in the literature (0.45 nm). Rutherford Backscattering Spectrometry studies and Channeling (RBS/C) showed that the GaN-layer is rich in N (Ga1.00N1.90, for 3 × 1017 N/cm2) and presents channeling (for implantations of 2 and 3 × 1017 N/cm2), corroborating the monocrystalline nature identified by TEM. Photoluminescence (PL) measurements confirm emission in the band gap region of a- GaN (~ 3.4 eV), as well as bands associated to structural defects in the material. It was also investigated the effect of strain fields from Helium (He) bubbles through synthesis starting up from He pre-implanted GaAs substrate. In this case, the bubbles, which are formed in the GaAs during the hot N-implantation and are annihilated after annealing, limit the N diffusion into the substrate, leading to the formation of a thicker GaN-layer (~ 120 nm) and with much more N (Ga1.00N2.80). As a result, the GaN-layer presented an aspect more polycrystalline.