Vertical cavity lasers (VCLs) are of great interest aslow-cost, high-performance light sources for fiber-opticcommunication systems. They have a number of advantages overconventional edge-emitting lasers, including low powerconsumption, efficient fiber coupling and wafer scalemanufacturing/testing. For high-speed data transmission overdistances up to a few hundred meters, VCLs (or arrays of VCLs)operating at 850 nm wavelength is today the technology ofchoice. While multimode fibers are successfully used in theseapplications, higher transmission bandwidth and longerdistances require single-mode fibres and longer wavelengths(1.3-1.55 µm). However, long-wavelength VCLs are as yetnot commercially available since no traditional materialssystem offers the required combination of bothhigh-index-contrast distributed Bragg reflectors (DBRs) andhigh-gain active regions. Earlier work on long-wavelength VCLshas therefore focused on hybrid techniques, such as waferfusion between InP-based QWs and AlGaAs DBRs, but more recentlythe main interest in this field has shifted towardsall-epitaxial GaAs-based devices employing novel 1.3-µmactive materials. Among these, strained GaInNAs/GaAs QWs aregenerally considered one of the most promising approaches andhave received a great deal of interest. The aim of this thesis is to investigate monolithicGaAs-based long-wavelength (&gt;1.2 µm) VCLs with InGaAsor GaInNAs QW active regions. Laser structures - or partsthereof - have been grown by metal-organic vapor phase epitaxy(MOVPE) and characterized by various techniques, such ashigh-resolution x-ray diffraction (XRD), photoluminescence(PL), atomic force microscopy, and secondary ion massspectroscopy (SIMS). High accuracy reflectance measurementsrevealed that n-type doping is much more detrimental to theperformance of AlGaAs DBRs than previously anticipated. Asystematic investigation was also made of the deleteriouseffects of buried Al-containing layers, such as AlGaAs DBRs, onthe optical and structural properties of subsequently grownGaInNAs QWs. Both these problems, with their potential bearingon VCL fabrication, are reduced by lowering the DBR growthtemperature. Record-long emission wavelength InGaAs VCLs were fabricatedusing an extensive gain-cavity detuning. The cavity resonancecondition just below 1270 nm wavelength occurs at the farlong-wavelength side of the gain curve. Still, the gain is highenough to yield threshold currents in the low mA-regime and amaximum output power exceeding 1 mW, depending on devicediameter. Direct modulation experiments were performed on1260-nm devices at 10 Gb/s in a back-to-back configuration withopen, symmetric eye diagrams, indicating their potential foruse in high-speed transmission applications. These devices arein compliance with the wavelength requirements of emerging10-Gb/s Ethernet and SONET OC-192 standards and may turn out tobe a viable alternative to GaInNAs VCLs. <b>Keywords:</b>GaInNAs, InGaAs, quantum wells, MOVPE, MOCVD,vertical cavity laser, VCSEL, long-wavelength, epitaxy, XRD,DBR

Photon detectors based on single-crystalline materials are of great interest for high performance imaging applications due to their low noise and fast response. The major detector materials for sensing in the long-wavelength infrared (LWIR) band (8-14 µm) are currently HgCdTe (MCT) and AlGaAs/GaAs quantum wells (QW) used in intraband-based quantum-well infrared photodetectors (QWIPs). These either suffer from compositional variations that are detrimental to the system performance as in the case of MCT, or, have an efficient dark current generation mechanism that limits the operating temperature as for QWIPs. The need for increased on-wafer uniformity and elevated operating temperatures has resulted in the development of various alternative approaches, such as type-II strained-layer superlattice detectors (SLSs) and intraband quantum-dot infrared photodetectors (QDIPs). In this work, we mainly explore two self-assembled quantum-dot (QD) materials for use as the absorber material in photon detectors for the LWIR, with the aim to develop low-dark current devices that can allow for high operating temperatures and high manufacturability. The detection mechanism is here based on type-II interband transitions from bound hole states in the QDs to continuum states in the matrix material. Metal-organic vapor-phase epitaxy (MOVPE) was used to fabricate (Al)GaAs(Sb)/InAs and In(Ga)Sb/InAs QD structures for the development of an LWIR active material. A successive analysis of (Al)GaAs(Sb) QDs using absorption spectroscopy shows strong absorption in the range 6-12 µm interpreted to originate in intra-valence band transitions. Moreover, record-long photoluminescence (PL) wavelength up to 12 µm is demonstrated in InSb- and InGaSb QDs. Mesa-etched single-pixel photodiodes were fabricated in which photoresponse is demonstrated up to 8 µm at 230 K with 10 In0.5Ga0.5Sb QD layers as the active region. The photoresponse is observed to be strongly temperature-dependent which is explained by hole trapping in the QDs. In the current design, the photoresponse is thermally limited at typical LWIR sensor operating temperatures (60-120 K), which is detrimental to the imaging performance. This can potentially be resolved by selecting a matrix material with a smaller barrier for thermionic emission of photo-excited holes. If such an arrangement can be achieved, type-II interband InGaSb QD structures can turn out to be interesting as a high-operating-temperature sensor material for thermal imaging applications. / <p>QC 20130521</p>

The design, fabrication, and characterizations of the spin-polarized AlxGa1-xN/GaN HEMT structure have been achieved for spintronic application. By band calculation within linear combination of atomic orbitals and two-band k·p methods, the theoretical spin-splitting energy and minimum-spin-splitting surface of wurtzite structure have been investigated as a function of the Fermi wavevector with various strain-relaxations. Base on these results, the design of host material of the nonballistic spin-FET has also been proposed. By optimizing the Al composition and n2DEG, the Fermi surface of two-dimensional electron gas is supposed to reach the minimum-spin-splitting surface to produce resonant spin-lifetime. Because the high quality AlxGa1-xN/GaN HEMT structure is necessary for realizing the spin-FET, the influence of the growth conditions on the polarity and structure quality of the GaN epilayer have been studied on the sample grown by plasma-assisted molecular beam epitaxy. Ga-polar AlGaN/GaN heterostructures on c-Al2O3 has been realized by growing over the Al-rich AlN nucleation layer. And the reduction of interface roughness and threading dislocation scatterings of the electrons in two-dimensional electron gas has also been achieved by growing GaN epilayer under slightly Ga-rich condition. Furthermore, the effect of different types of threading dislocation on the electron mobility of the AlxGa1-xN/GaN HEMT structure has been investigated as well. At low temperature, the electron mobility of two-dimensional electron gas in AlGaN/GaN heterostructures is majorly scattered by the edge type dislocation rather than the screw type. The designs of proposed host material for spin-FETs have been realized through growing high quality spin-polarized AlxGa1-xN/GaN HEMT structures with various Al composition (x= 0.191 ¡V 0.397) grown on c-Al2O3 by metalorganic vapor phase epitaxy. The high mobility (10682 cm2/Vs at 0.4 K), flat interface (surface roughness < 0.5 nm), and high quality HEMT provide a good environment to study the spin-splitting energy. To investigate the spin-splitting energy as functions of the Fermi wavevector, the Shubnikov-de Haas measurements were performed. A large spin-splitting energy (10.76 meV) has been fabricated in Al0.390Ga0.61N/GaN HEMT structure with kf = 8.14 ¡Ñ 108 m-1 for the host material of the Datta-Das spin-FET. And for the first time, the minimum-spin-splitting surface has been experimentally generated in Al0.390Ga0.61N/GaN HEMT structure with kf = 8.33 ¡Ñ 108 m-1 for the host material of the nonballistic spin-FET.

<p>Vertical cavity lasers (VCLs) are of great interest aslow-cost, high-performance light sources for fiber-opticcommunication systems. They have a number of advantages overconventional edge-emitting lasers, including low powerconsumption, efficient fiber coupling and wafer scalemanufacturing/testing. For high-speed data transmission overdistances up to a few hundred meters, VCLs (or arrays of VCLs)operating at 850 nm wavelength is today the technology ofchoice. While multimode fibers are successfully used in theseapplications, higher transmission bandwidth and longerdistances require single-mode fibres and longer wavelengths(1.3-1.55 µm). However, long-wavelength VCLs are as yetnot commercially available since no traditional materialssystem offers the required combination of bothhigh-index-contrast distributed Bragg reflectors (DBRs) andhigh-gain active regions. Earlier work on long-wavelength VCLshas therefore focused on hybrid techniques, such as waferfusion between InP-based QWs and AlGaAs DBRs, but more recentlythe main interest in this field has shifted towardsall-epitaxial GaAs-based devices employing novel 1.3-µmactive materials. Among these, strained GaInNAs/GaAs QWs aregenerally considered one of the most promising approaches andhave received a great deal of interest.</p><p>The aim of this thesis is to investigate monolithicGaAs-based long-wavelength (>1.2 µm) VCLs with InGaAsor GaInNAs QW active regions. Laser structures - or partsthereof - have been grown by metal-organic vapor phase epitaxy(MOVPE) and characterized by various techniques, such ashigh-resolution x-ray diffraction (XRD), photoluminescence(PL), atomic force microscopy, and secondary ion massspectroscopy (SIMS). High accuracy reflectance measurementsrevealed that n-type doping is much more detrimental to theperformance of AlGaAs DBRs than previously anticipated. Asystematic investigation was also made of the deleteriouseffects of buried Al-containing layers, such as AlGaAs DBRs, onthe optical and structural properties of subsequently grownGaInNAs QWs. Both these problems, with their potential bearingon VCL fabrication, are reduced by lowering the DBR growthtemperature.</p><p>Record-long emission wavelength InGaAs VCLs were fabricatedusing an extensive gain-cavity detuning. The cavity resonancecondition just below 1270 nm wavelength occurs at the farlong-wavelength side of the gain curve. Still, the gain is highenough to yield threshold currents in the low mA-regime and amaximum output power exceeding 1 mW, depending on devicediameter. Direct modulation experiments were performed on1260-nm devices at 10 Gb/s in a back-to-back configuration withopen, symmetric eye diagrams, indicating their potential foruse in high-speed transmission applications. These devices arein compliance with the wavelength requirements of emerging10-Gb/s Ethernet and SONET OC-192 standards and may turn out tobe a viable alternative to GaInNAs VCLs.</p><p><b>Keywords:</b>GaInNAs, InGaAs, quantum wells, MOVPE, MOCVD,vertical cavity laser, VCSEL, long-wavelength, epitaxy, XRD,DBR</p>

Ce travail traite de la croissance épitaxiale et de la caractérisation d’hétérostructures àbase de multi-puits quantiques (MPQ) pour des applications dans le photovoltaïque. Leséchantillons ont été obtenus par la technique d’épitaxie en phase vapeur aux organométalliques(EPVOM) sur des substrats de saphir (0001). La caractérisation structurale etoptique est réalisée par diffraction de rayons X, microscopie électronique en transmission,spectroscopie de photoluminescence et de transmission. Pour étudier la présence de l’effetphotovoltaïque et pour estimer la performance électrique des échantillons, les MPQ ont étéintégrés dans la géométrie de cellules solaires en utilisant de la photolithographie, desattaques réactives ioniques assistées par plasma inductif et des métallisations pour contacterles parties dopées n et p.Nous avons étudié l’influence de différents designs des régions actives InGaN/GaN surles propriétés optiques et électriques des échantillons, c’est-à-dire le nombre de puitsquantiques InGaN, les épaisseurs des puits et des barrières et la composition en indium dansles puits. Deux mécanismes principaux doivent être pris en compte pour une optimisationefficace de composants photovoltaïques: l’absorption des photons et la collections desporteurs. Nous avons montré qu’une augmentation du nombre de MPQ, de leur épaisseur etde la composition d’In améliorait l’absorption, mais causait aussi des pertes dans l’efficacitéde collection du fait de l’augmentation de l’épaisseur de la couche active (champ électriqueplus faible), de la difficulté des porteurs pour s’échapper de puits plus profonds et derelaxation des contraintes (création de défauts structuraux). La décroissance de l’épaisseur desbarrières peut résoudre les deux premiers points, mais le problème de la relaxation de lacontrainte reste entier. Pour notre meilleur design, nous obtenons une efficacité de conversionde 2 % pour des couches 15×In0.18Ga0.82N/GaN qui ont une réponse spectrale qui s’étendjusqu’à 465 nm. / In this work we report on epitaxial growth and characterization of InGaN/GaN multiquantumwells (MQWs) heterostructures for application in photovoltaic devices. The sampleswere grown by metal-organic vapor phase epitaxy (MOVPE) on (0001) sapphire substrate.The structural and optical characterization is performed by X-ray diffraction, transmissionelectron microscopy, photoluminescence spectroscopy and transmission measurements. Toinvestigate the presence of photovoltaic effect and estimate the electrical performance of thesamples, they were processed into solar cells by means of the photolithography, inductivelycoupled plasma reactive-ion etching and metallization to manage n and p contacts.We studied the influence of different InGaN/GaN active region designs on thestructural, optical and electrical properties of the samples, i.e. number of InGaN quantumwells, QW and quantum barrier thicknesses and indium composition in the wells. Two mainmechanisms have to be taken into account for an efficient optimization of photovoltaicdevices: photon absorption and carrier collection. We showed that an increase of the MQWsnumber, their thickness and the In-content allows absorption improvement, but causes lossesin the carrier collection efficiency due to: the increase of the active region thickness (lowerelectric field), the difficulty of the carrier to escape from deeper QWs and the strain relaxation(structural defect creation). The decrease of the barrier thickness can solve the first two issues,but the problem with strain relaxation remains. In the best design, we report the value of2.00% of conversion efficiency for 15×In0.18Ga0.82N/GaN samples with spectral responseextending to 465 nm.

Ce travail traite de la croissance épitaxiale et de la caractérisation d’hétérostructures àbase de multi-puits quantiques (MPQ) pour des applications dans le photovoltaïque. Leséchantillons ont été obtenus par la technique d’épitaxie en phase vapeur aux organométalliques(EPVOM) sur des substrats de saphir (0001). La caractérisation structurale etoptique est réalisée par diffraction de rayons X, microscopie électronique en transmission,spectroscopie de photoluminescence et de transmission. Pour étudier la présence de l’effetphotovoltaïque et pour estimer la performance électrique des échantillons, les MPQ ont étéintégrés dans la géométrie de cellules solaires en utilisant de la photolithographie, desattaques réactives ioniques assistées par plasma inductif et des métallisations pour contacterles parties dopées n et p.Nous avons étudié l’influence de différents designs des régions actives InGaN/GaN surles propriétés optiques et électriques des échantillons, c’est-à-dire le nombre de puitsquantiques InGaN, les épaisseurs des puits et des barrières et la composition en indium dansles puits. Deux mécanismes principaux doivent être pris en compte pour une optimisationefficace de composants photovoltaïques: l’absorption des photons et la collections desporteurs. Nous avons montré qu’une augmentation du nombre de MPQ, de leur épaisseur etde la composition d’In améliorait l’absorption, mais causait aussi des pertes dans l’efficacitéde collection du fait de l’augmentation de l’épaisseur de la couche active (champ électriqueplus faible), de la difficulté des porteurs pour s’échapper de puits plus profonds et derelaxation des contraintes (création de défauts structuraux). La décroissance de l’épaisseur desbarrières peut résoudre les deux premiers points, mais le problème de la relaxation de lacontrainte reste entier. Pour notre meilleur design, nous obtenons une efficacité de conversionde 2 % pour des couches 15×In0.18Ga0.82N/GaN qui ont une réponse spectrale qui s’étendjusqu’à 465 nm. / In this work we report on epitaxial growth and characterization of InGaN/GaN multiquantumwells (MQWs) heterostructures for application in photovoltaic devices. The sampleswere grown by metal-organic vapor phase epitaxy (MOVPE) on (0001) sapphire substrate.The structural and optical characterization is performed by X-ray diffraction, transmissionelectron microscopy, photoluminescence spectroscopy and transmission measurements. Toinvestigate the presence of photovoltaic effect and estimate the electrical performance of thesamples, they were processed into solar cells by means of the photolithography, inductivelycoupled plasma reactive-ion etching and metallization to manage n and p contacts.We studied the influence of different InGaN/GaN active region designs on thestructural, optical and electrical properties of the samples, i.e. number of InGaN quantumwells, QW and quantum barrier thicknesses and indium composition in the wells. Two mainmechanisms have to be taken into account for an efficient optimization of photovoltaicdevices: photon absorption and carrier collection. We showed that an increase of the MQWsnumber, their thickness and the In-content allows absorption improvement, but causes lossesin the carrier collection efficiency due to: the increase of the active region thickness (lowerelectric field), the difficulty of the carrier to escape from deeper QWs and the strain relaxation(structural defect creation). The decrease of the barrier thickness can solve the first two issues,but the problem with strain relaxation remains. In the best design, we report the value of2.00% of conversion efficiency for 15×In0.18Ga0.82N/GaN samples with spectral responseextending to 465 nm.

Long-wavelength (1.3-μm) vertical-cavity surface-emitting lasers (VCSELs) are of great interest as low-cost, high performance light sources for fiber-optic metro and access networks. During recent years the main development effort in this field has been directed towards all epitaxial GaAs-based structures by employing novel active materials. Different active region candidates for GaAs-based 1.3-μm VCSELs such as GaInNAs/GaAs QWs, GaAsSb QWs or InAs/InGaAs QDs have been investigated. However, the difficult growth and materials properties of these systems have so far hampered any real deployment of the technology. More recently, a new variety of VCSELs have been developed at KTH as based on highly strained InGaAs QWs and negative gain cavity detuning to reach the 1.3-μm wavelength window. The great benefit of this approach is that it is fully compatible with standard materials and processing methods. The aim of this thesis is to investigate long-wavelength (1.3-μm) VCSELs using ~1.2-μm In0.4GaAs/GaAs Multiple Quantum Wells (MQWs). A series of QW structures, DBR structures and laser structures, including VCSELs and Broad Area lasers (BALs) were grown by metal-organic vapor phase epitaxy (MOVPE) and characterized by various techniques: Photoluminescence (PL), high-resolution x-ray diffraction (XRD), atomic force microscopy (AFM), high accuracy reflectance measurements as well as static and dynamic device characterization. The work can be divided into three parts. The first part is dedicated to the optimization and characterization of InGaAs/GaAs QWs growth for long wavelength and strong luminescence. A strong sensitivity to the detailed growth conditions, such as V/III ratio and substrate misorientation is noted. Dislocations in highly strained InGaAs QW structure and Sb as surfactant assisted in InGaAs QW growth are also discussed here. The second part is related to the AlGaAs/GaAs DBR structures. It is shown that the InGaAs VCSELs with doped bottom DBRs have significantly lower slope efficiency, output power and higher threshold current. By a direct study of buried AlGaAs/GaAs interfaces, this is suggested to be due to doping-enhanced Al-Ga hetero-interdiffusion. In the third part, singlemode, high-performance 1.3-μm VCSELs based on highly strained InGaAs QWs are demonstrated. Temperature stable singlemode performance, including mW-range output power and 10 Gbps data transmission, is obtained by an inverted surface relief technique. / QC 20101126

In dieser Arbeit untersuchen wir die grundlegenden Wachstums- und Relaxationsprozesse, die es erlauben den Verzerrungszustand von GaN (0001) beim Wachstum auf Silizium (111) Substraten einzustellen und die resultierende Dichte an Durchstoßversetzungen zu reduzieren. Zu deren Analyse werden GaN (0001) Schichten, die mittels metallorganischer Gasphasenepitaxy abgeschieden worden sind, hauptsächlich mit transmissionselekronenmikroskopischen Methoden untersucht. Die wesentlichen Erkenntnisse der Arbeit sind: (i) Der Aufbau einer kompressiven Verzerrung von GaN (0001) Filmen mittels AlGaN Zwischenschichten beruht auf einer Asymmetrie der plastischen Relaxation an den beiden Grenzflächen der AlGaN Zwischenschicht. Fehlpassungsversetzungen bilden sich zwar an beiden Grenzflächen aus, jedoch ist der mittlere Abstand zwischen Versetzungslinien an der unteren Grenzfläche kleiner, als an der oberen. (ii) Plastische Relaxation von verzerrten (0001) Wurtzit Schichten erfolgt im Wesentlichen durch Bildung von a-Typ Fehlpassungsversetzungen im 1/3 |{0001} Gleitsystem. Diese bilden sich aber nur dann, wenn die verzerrten Schichten eine 3-D Morphologie aufweisen. Eine quantitative Modellierung dieses Prozesses zeigt, dass die kritische Schichtdicke für das Einsetzen der plastischen Relaxation wesentlich vom Wachstumsmodus bestimmt wird. (iii) Eine Silizium Delta-Dotierung der GaN (0001) Oberfläche führt zum Wachstum einer kohärenten Sub-Monolage SiGaN3, die eine periodisch Anordnung von Silizium- und Galliumatomen, sowie Galliumvakanzen aufweist. Da das Wachstum von GaN direkt auf der SiGaN3-Monolage unterdrückt ist, tritt ein Übergang zu 3-D Inselwachstum auf, das zunächst ausschließlich in Löchern der SiGaN3-Monolage anfängt. Eine hohe Konzentration von Silizium auf der GaN (0001) Oberfläche wirkt also als Anti-Surfactant beim epitaktischen Wachstum von GaN. Rechnungen mittels der Dichtefunktionaltheorie liefern Erklärungen für das beobachtete Wachstumsverhalten. / In this work we study the basic growth and relaxation processes that are used for strain and dislocation engineering in the growth of GaN (0001) films on silicon (111) substrates. To analyse these processes, samples, grown by metalorganic vapour phase epitaxy were investigate by means of transmission electron microscopy. Our investigations have revealed the following main results: (i) Strain engineering and build-up of compressive strain in GaN (0001) films by means of AlGaN interlayer is based on an asymmetry in plastic relaxation between the two interfaces of the AlGaN interlayer. Although misfit dislocation networks form at both interfaces of the interlayer, the average spacing of dislocation lines at the lower interface is smaller than that at the upper one. (ii) Plastic relaxation of strained (0001) wurtzite films is caused mainly by formation of a-type misfit dislocations in the 1/3 |{0001} slip-system. These a-type misfit dislocations form once the strained films undergo a transition to a 3-D surface morphology, e.g. by island growth or cracking. Quantitative modelling of this process reveals that the critical thickness for nucleation of a-type misfit dislocations depends next to the lattice mismatch mainly on the growth mode of the film. (iii) Silicon delta-doping of the GaN (0001) surface leads to the growth of a coherent sub-monolayer of SiGaN3 that shows a periodic arrangement of silicon and gallium atoms and gallium vacancies. Since growth of thick GaN layers directly on top of the SiGaN3-monolayer is inhibited a transition towards 3-D island growth occurs, whereby GaN islands exclusively nucleate at openings in the SiGaN3-monolayer. A high concentration of silicon on the GaN (0001) surface thus acts as an anti-surfactant in the epitaxial growth of GaN. Our density functional theory calculations provide an explanation for both the self-limited growth of the SiGaN3-monolayer, as well as for the blocking of GaN growth on top of the SiGaN3-monolayer.

En raison de leurs applications prometteuses dans les domaines de l'optoélectronique et de l'électronique, les semiconducteurs III-V à base d'azote: les nitrures (AlN, GaN, InN) et leurs alliages (InAlN, InGaN, AlGaN), font l'objet, depuis les années 1990, d'une activité intense en recherche et développement. Dans ce travail, nous avons étudié les propriétés structurales des couches d'InN et de l'alliage InAlN dans les hétérostructures InAlN/AlN/GaN et InAlN/GaN en combinant les techniques AFM, IBA, DRXHR, Raman et MET. L'étude des couches d'InN a été menée par DRX afin de déterminer la contrainte résiduelle, et on a cherché à faire une corrélation avec la morphologie des surfaces par AFM. Les contraintes résiduelles obtenues par DRX ont été comparées aux résultats de spectroscopie Raman, et on a pu montrer que toutes les couches avaient une contrainte résiduelle qui n'est pas purement bi-axiale. Les hétérostructures InAlN pour transistors à haute mobilité électronique (HEMTs) sont des couches ultraminces de quelques monocouches atomiques à plusieurs dizaines de nanomètres d'épaisseur. De plus, leur structure peut être assez complexe dans le but d'optimiser le gaz d'électrons généré dans le canal du transistor. Dans l'idéal, on utilise une concentration en indium autour de 17%, qui est celle de l'accord de paramètres cristallins avec le GaN. Nos travaux ont mis en évidence qu'il n'est pas facile de contrôler la composition locale; en effet la structure et morphologie des couches sont très sensibles aux conditions de croissance.

Les diodes électroluminescentes (LEDs) utilisées dans les systèmes d'éclairage solide sont réalisées à base de GaN et de ses alliages. Bien que les LEDs commerciales soient principalement développées sur substrat saphir, les industriels et laboratoires de recherche s'intéressent également au substrat silicium, moins cher et disponible en de plus grands diamètres. Son utilisation pose cependant deux problèmes : la présence d'une importante densité de dislocations dans les couches épitaxiées et la mise en tension de celles-ci menant à l'apparition de fissures. Afin de les éviter, des solutions existent mais nécessitent des procédés de croissance longs et complexes entraînant une augmentation du coût de production.L'alternative proposée au cours de cette thèse consiste en la croissance sélective de pseudo-substrats de GaN sur silicium par épitaxie en phase vapeur aux organométalliques (EPVOM). La croissance sélective doit en effet permettre l'obtention d'un matériau de bonne qualité cristalline présentant une contrainte limitée (en évitant la coalescence) tout en réduisant la durée d'épitaxie. Nos travaux ont porté sur l'analyse de l'influence des paramètres de croissance (conditions de croissance, design du masque, polarité du substrat) afin de comprendre les mécanismes mis en jeu et de maîtriser l'effet de chacun d'eux sur la morphologie du matériau. La croissance de pseudo-substrats de GaN hexagonal [000-1] sur du Si (100) a été démontrée grâce à l'utilisation d'une couche texturée d'AlN de polarité N. Des caractérisations optiques et structurales ont démontré une relaxation de la contrainte ainsi qu'une bonne qualité cristalline du matériau à la surface de ces structures. La croissance sur celles-ci de multi-puits quantiques (MQWs) InGaN/GaN a ensuite été étudiée pour la réalisation de micro-LEDs. Cependant, des difficultés ont été rencontrées du fait de la présence d'inversions de polarité dans les pseudo-substrats. Ces essais ont également mis en évidence la nécessité d'une étude à part entière de la croissance de MQWs de polarité N. / Light-emitting diodes (LEDs) used in solid lighting systems are made from GaN and its alloys. Although commercial LEDs are mainly developed on sapphire substrate, manufacturers and research laboratories are also interested in silicon substrate, which is cheaper and available in larger diameters. However, its usage raises two issues: the presence of a high dislocation density in epitaxial layers and their tensile stress leading to the formation of cracks. In order to avoid them, solutions exist but require long and complex growth processes resulting in an increase in production costs.The alternative proposed in this thesis is focused on the selective area growth of GaN pseudo-substrates on silicon by metalorganic vapour phase epitaxy (MOVPE). Indeed, selective area growth should make it possible to obtain a good crystalline material displaying a limited stress (avoiding coalescence) while reducing epitaxy duration. Our work focused on the analysis of the influence of growth parameters (growth conditions, mask design, substrate polarity) in order to understand the involved mechanisms and to control the effect of each of them on the material morphology. The growth of hexagonal [000-1] GaN pseudo-substrates on Si (100) was demonstrated by using a textured N-polar AlN layer. Optical and structural characterisations displayed a stress relaxation as well as a good crystalline quality of these structures’ surface material. The growth on top of those of InGaN/GaN multiple quantum wells (MQWs) was then studied for micro-LEDs realisation. However, difficulties have been encountered due to the presence of polarity inversions in pseudo-substrates. These tests also demonstrated the necessity of a complete study of N-polar MQWs growth.