Ce travail porte sur la croissance par épitaxie sous jets moléculaires (EJM) et sur les propriétés structurales et optiques de boîtes quantiques (BQs) AlyGa1-yN insérées dans une matrice AlxGa1-xN (0001). L’objectif principal est d’étudier le potentiel des BQs en tant que nouvelle voie pour la réalisation d’émetteurs ultraviolets (UV) efficaces.Tout d'abord, nous avons étudié la croissance des BQs GaN en utilisant soit une source plasma (N2, appelée PAMBE) soit une source ammoniac (NH3, appelée NH3-MBE) afin de choisir la meilleure approche pour former les BQs les plus efficaces. Il a été montré que le procédé de croissance est mieux contrôlé en utilisant l’approche PAMBE, conduisant à la croissance de BQs GaN avec des densités plus élevées, une meilleure uniformité en taille et des intensités de photoluminescence (PL) jusqu’à trois fois plus élevées. En outre, l'influence de la contrainte épitaxiale sur le processus d'auto-assemblage des BQs a été étudiée en fabriquant des BQs GaN sur différentes couche tremplins d’AlxGa1-xN (avec 0,5 ≤ x ≤ 0,7). Nous avons montré que des BQs avec des densités plus élevées et des hauteurs plus faibles sont formées en augmentant le désaccord de paramètre de maille (c.à.d en utilisant des tremplins avec xAl plus élevé). Cependant, les mesures de photoluminescence (PL) indiquent un fort décalage de l'énergie d'émission vers le rouge lorsque xAl augmente, en raison de l'augmentation de la discontinuité du champ électrique interne de 3 à 5,3 MV/cm.Ensuite, des études approfondies sur les conditions de croissance et les propriétés optiques des BQs Al0,1Ga0,9N / Al0,5Ga0,5N ont été présentées, montrant les différents défis pour fabriquer des BQs efficaces. L’optimisation de la procédure de croissance, notamment l’étape de recuit post-croissance, a montré une modification de la forme des BQs. Plus précisément, un changement d’une forme allongée (pour un recuit à 740 °C), à une forme symétrique (pour un recuit à une température proche de ou supérieure à 800°C) a été observé. En plus, une bande d’émission supplémentaire vers les plus grandes longueurs d’onde a également été observée pour les BQs formées avec un recuit à 740°C. Cette bande a été attribuée à une fluctuation de composition des BQs, induisant la formation d’une famille additionnelle de BQs avec des hauteurs plus grandes et une compostions en Al inférieure à 10 %, estimée proche de l’alliage binaire GaN. Enfin, il a été démontré qu’en faisant un recuit à plus haute température (≥ 800°C), l’émission de PL de cette famille supplémentaire de BQs (BQs riche en Ga ou (Al)GaN) diminue très fortement. De plus, cette étape de recuit impacte fortement la forme des BQs et a conduit à une amélioration de leur efficacité radiative d’un facteur 3. Ensuite, la variation de la composition en Al des BQs AlyGa1-yN (0,1 ≤ y ≤ 0,4), ainsi que la quantité de matière déposée ont permis d’évaluer la gamme de longueurs d’onde d’émission accessibles. En ajustant les conditions de croissance, l’émission des BQs a été déplacée de l’UVA vers l’UVC, atteignant une émission autour de 270 - 275 nm (pour les applications de purification de l’eau et de l’air) avec des rendements radiatifs élevés. Les mesures de photoluminescence résolue en temps (TRPL), combinées avec les mesures de PL en fonction de la température, nous ont permis de déterminer les efficacités quantiques internes (IQE) des BQs GaN / AlxGa1-xN (0001). Des valeurs d’IQE comprises entre 50 % et 66 % ont été obtenues à basse température, avec la possibilité d’atteindre un rapport d’intensité intégré de PL, entre 300 K et 9 K, allant jusqu’à 75 % pour les BQs GaN et 46 % pour les BQs AlyGa1-yN (contre 0,5 % pour des structures équivalents à base de puits quantiques).Enfin, nous avons montré la possibilité de fabriquer des DELs à base de BQs (Al,Ga)N couvrant une grande gamme de longueurs d’onde allant du bleu-violet jusqu’à l’UVB (de 415 nm à 305 nm). / This PhD deals with the epitaxial growth, structural and optical properties of AlyGa1-yN quantum dots (QDs) grown on AlxGa1-xN (0001) by molecular beam epitaxy (MBE), with the aim to study their potential as a novel route for efficient ultraviolet (UV) emitters.First, we have studied the growth of GaN QDs using either plasma MBE (PAMBE) or ammonia MBE (NH3-MBE) to find the most adapted nitrogen source for the fabrication of UV emitting QDs. It was shown that the growth process is better controlled using PAMBE, leading to the growth of GaN QDs with higher densities, better size uniformity and up to three times higher photoluminescence (PL) intensities. Also, the influence of the epitaxial strain on the QD self-assembling process was studied by fabricating GaN QDs on different AlxGa1-xN surfaces (with 0.5 ≤ x ≤ 0.7). We showed that QDs with higher densities and smaller sizes (heights) are formed by using a larger lattice-mismatch (i.e. a higher xAl composition). However, photoluminescence (PL) measurements indicated a strong redshift in the emission energy as the Al content of the AlxGa1-xN template increases due to the increase of the internal electric field discontinuity from 3 to 5.3 MV/cm.Next, in-depth investigations of the growth conditions and optical properties of Al0.1Ga0.9N QDs / Al0.5Ga0.5N were done presenting the different challenges to be solved to grow efficient QDs. Changing the growth procedure, especially the post-growth annealing step, has shown a modification of the QD shape from elongated QDs, formed with an annealing at 740°C, to symmetric QDs, formed with an annealing at a temperature around or above 800°C. An additional band emission at lower energies was also observed for QDs grown with a lower annealing temperature (740°C). This additional band emission was attributed to the formation of QDs with higher heights and a reduced Al composition less than the nominal one of 10 % (i.e. forming Ga-rich QDs). The influence of the annealing step performed at higher temperature has been shown to strongly decrease the PL emission from this additional QD family. In addition, this annealing step strongly impacted the QD shape and led to an improvement of the QD radiative efficiency by a factor 3. Then, the AlxGa1-xN barrier composition (0.5 ≤ x ≤ 0.7), the AlyGa1-yN QD composition (0.1 ≤ y ≤ 0.4) as well as the deposited amount were varied in order to assess the range of accessible emission energies. Also, the influence of varying the AlxGa1-xN barrier composition on the QD formation was studied. By varying these growth conditions, the QD wavelength emission was shifted from the UVA down to the UVC range, reaching a minimum wavelength emission of 270 - 275 nm (for water and air purification applications) with a high radiative efficiency. Time resolved photoluminescence (TRPL) combined with temperature dependent PL measurements enabled us to determine the internal quantum efficiencies (IQE) of AlyGa1-yN QDs / AlxGa1-xN (0001). IQE values between 50 % and 66 % were found at low temperature, combined with the ability to reach a PL integrated intensity ratio, between 300 K and 9 K, up to 75 % for GaN QDs and 46 % for AlyGa1-yN QDs (versus 0.5 % in a similar quantum well structure emitting in the UVC range).Finally, the demonstration of AlyGa1-yN QD-based light emitting diode prototypes, emitting in the whole UVA range, using GaN and Al0.1Ga0.9N QDs, and in the UVB range down to 305 nm with Al0.2Ga0.8N QDs active regions, was shown.

Os fotodetectores infravermelhos baseados em pontos quânticos (Quantum-dot Infrared Photodetectors, QDIPs) surgiram recentemente como uma nova tecnologia para a detecção de radiação infravermelha. Comparados com fotodetectores mais convencionais baseados em poços quânticos (Quantum-well Infrared Photodetectors, QWIPs), as suas vantagens se originam no confinamento tridimensional de portadores e incluem a sensibilidade intrínseca à incidência normal de luz, um maior tempo de vida dos portadores fotoexcitados e uma baixa corrente de escuro, que devem permitir o funcionamento dos dispositivos acima das temperaturas criogênicas. No presente trabalho, a técnica de epitaxia por feixe molecular (Molecular-Beam Epitaxy - MBE) foi usada para crescer várias amostras de QDIPs de InAs/GaAs com o objetivo de estudar a inuência dos parâmetros estruturais destes dispositivos. Após o crescimento, as amostras foram processadas em pequenas mesas quadradas por técnicas de litografia convencional e, então, caracterizadas. As propriedades ópticas e eletrônicas dos dispositivos foram verificadas para temperaturas a partir de 10 K. Com o objetivo de realizar medidas eletrônicas de alta qualidade, janelas de Ge e cabos com conectores de baixo ruído para baixa temperatura foram empregados. As curvas de corrente de escuro, as curvas de responsividade com corpo negro (fotocorrente), as medições do ruído com uma analisador de sinais e as respostas espectrais por FTIR (Fourier Transform Infrared) forneceram um conjunto completo de informações sobre os dispositivos. As figuras de mérito dos nossos melhores dispositivos permitiram também, determinar a probabilidade de captura e o ganho fotocondutivo. Com o intuito de compreender a relação entre as dimensões físicas dos pontos quânticos e as características de funcionamento dos QDIPs, desenvolveu-se um cálculo dos estados eletrônicos de da função de onda de um elétron confinado em um ponto quântico de InxGa1-xAs em formato de lente, envolvido em uma matriz de GaAs, com massas efetivas dependentes da posição. Esse modelo leva em conta o efeito da tensão assim como o gradiente de In dentro do ponto quântico, resultante do forte efeito de segregação presente em um sistema de InxGa1-xAs/GaAs. Diferentes perfis de segregação foram testados com o nosso modelo teórico com vista a proporcionar o melhor ajuste os nossos dados experimentais. / Quantum-dot Infrared Photodetectors (QDIPs) recently emerged as a new technology for detecting infrared radiation. Compared to more conventional photodetectors based on quantum wells (QWIPs), their advantages originate from the three-dimensional confinement of carriers and include an intrinsic sensitivity to normal incidence of light, a longer lifetime of the photoexcited carriers and a lower dark current which should hopefully allow their operation close to room temperature. In the present work, molecular-beam epitaxy (MBE) was used to grow several InAs/GaAs QDIP samples in order to analyse the influence the structural properties of such devices. After the growth, the samples were processed into small squared mesas by conventional lithography techniques and fully characterized. The optical and electrical properties of the devices were checked as a function of temperature using Ge optical windows and all the connectors and low-temperature/low-noise cables needed to perform high quality low-level electrical measurements. Dark-current curves, Responsivity (photocurrent) data with a black body, noise measurements with a signal analyzer and spectral responses by FTIR provided a full set of information about the devices. The figures of merit of our best devices allowed us also to determine the capture probability and the photoconductive gain. In order to understand the relationship between the physical dimensions of the quantum dots and the operating characteristics of the QDIPs, we developed a position-dependent effective-mass calculation of the bound energy levels and wave function of the electrons confined in lensshaped InxGa1-xAs quantum dots embedded in GaAs, taking into account the strain as well as the In gradient inside the quantum dots which is due to the strong In segregation and intermixing present in the InxGa1-xAs/GaAs system. Different In profiles inside the quantum dots were tested with our new theoretical model in order to provide the best _t to our experimental data.

<p>Bismuth titanate Bi₄Ti₃O₁₂, is one of the bismuth based layered ferroelectric materials that is a candidate for replacing the lead based ferroelectric materials in for instance non-volatile ferroelectric random access memories (FRAM). This is due to the fact that the bismuth based ferroelectrics consists of pseudo perovskite units sandwiched in between bismuth oxide layers, which gives them a better fatigue nature.</p><p>In this thesis thin films of Bi₄Ti₃O₁₂have been deposited by chemical vapour deposition (CVD) using the metal iodides, BiI₃ and TiI₄ as precursors. Films grown on MgO(001) substrates were found to grow epitaxially. The electrical properties were determined for films grown on Pt-coated silicon and good properties such as a high dielectric constant (ε) of 200, low <i>tan</i> δ of 0.018, a remnant polarisation (<i>P</i>_r) of 5.3 μC/cm² and coercive field (E_c) as high as 150 kV/cm were obtained. Thin films in the Bi-Ti-O system were also deposited by atomic layer deposition (ALD) using metalorganic precursors.</p><p>In addition to the ternary bismuth titanates, films in the binary oxide systems <i>i.e.</i> bismuth oxides and titanium oxides were deposited. Epitaxial TiO₂ films were deposited both by CVD and ALD using TiI₄ as precursor. The rutile films deposited by ALD were found to grow epitaxially down to a temperature of at least 375 ¢ªC on α-A1₂O₃(0 1 2) substrates. The TiO₂ ALD process was also studied <i>in-situ</i> by QCM. Different bismuth oxides were deposited by halide-CVD using BiI₃ as precursor on MgO(0 0 1) and SrTiO₃(0 0 1) substrates and the results were summarised in an experimental CVD stability diagram. The Bi₂O_2.33 phase was found to grow epitaxially on both substrates.</p>

Bismuth titanate Bi4Ti3O12, is one of the bismuth based layered ferroelectric materials that is a candidate for replacing the lead based ferroelectric materials in for instance non-volatile ferroelectric random access memories (FRAM). This is due to the fact that the bismuth based ferroelectrics consists of pseudo perovskite units sandwiched in between bismuth oxide layers, which gives them a better fatigue nature. In this thesis thin films of Bi4Ti3O12 have been deposited by chemical vapour deposition (CVD) using the metal iodides, BiI3 and TiI4 as precursors. Films grown on MgO(001) substrates were found to grow epitaxially. The electrical properties were determined for films grown on Pt-coated silicon and good properties such as a high dielectric constant (ε) of 200, low tan δ of 0.018, a remnant polarisation (Pr) of 5.3 μC/cm2 and coercive field (Ec) as high as 150 kV/cm were obtained. Thin films in the Bi-Ti-O system were also deposited by atomic layer deposition (ALD) using metalorganic precursors. In addition to the ternary bismuth titanates, films in the binary oxide systems i.e. bismuth oxides and titanium oxides were deposited. Epitaxial TiO2 films were deposited both by CVD and ALD using TiI4 as precursor. The rutile films deposited by ALD were found to grow epitaxially down to a temperature of at least 375 ¢ªC on α-A12O3(0 1 2) substrates. The TiO2 ALD process was also studied in-situ by QCM. Different bismuth oxides were deposited by halide-CVD using BiI3 as precursor on MgO(0 0 1) and SrTiO3(0 0 1) substrates and the results were summarised in an experimental CVD stability diagram. The Bi2O2.33 phase was found to grow epitaxially on both substrates.

Semiconductor lasers based on gallium arsenide and relatedmaterials are widely used in applications such as opticalcommunication systems, sensing, compact disc players, distancemeasurement, etc. The performance of these lasers can beimproved using a buried heterostructure offering lateralcarrier and optical confinement. In particular, if theconfinement (burying) layer is implemented by epitaxialregrowth of an appropriate aluminium-free semi-insulating (SI)material, passivation of etched surfaces, reduced tendency tooxidation, low capacitance and integration feasibility areadditional advantages. The major impediment in the fabrication of GaAs/AlGaAsburied-heterostructure lasers is the spontaneous oxidation ofaluminium on the etched walls of the structure. Al-oxide actsas a mask and makes the regrowth process extremely challenging.In this work, a HCl gas-basedin-situcleaning technique is employed successfully toremove Al-oxide prior to regrowth of SI-GaInP:Fe and SI-GaAs:Fearound Al-containing laser mesas by Hydride Vapour PhaseEpitaxy. Excellent regrowth interfaces, without voids, areobtained, even around AlAs layers. Consequences of usinginadequate cleaning treatments are also presented. Regrowthmorphology aspects are discussed in terms of different growthmechanisms. Time-resolved photoluminescence characterisation indicates auniform Fe trap distribution throughout the regrown GaInP:Fe.Scanning capacitance microscopy measurements demonstrate thesemi-insulating nature of the regrown GaInP:Fe layer. Thepresence of EL2 defects in regrown GaAs:Fe makes more difficultthe interpretation of the characterisation results in the nearvicinity of the laser mesa. GaAs/AlGaAs buried-heterostructure lasers, both in-planelasers and vertical-cavity surface-emitting lasers, withGaInP:Fe as burying layer are demonstrated for the first time.The lasers exhibit good performance demonstrating thatSI-GaInP:Fe is an appropriate material to be used for thispurpose and the suitability of our cleaning and regrowth methodfor the fabrication of this type of semiconductor lasers.Device characterisation indicates negligible leakage currentalong the etched mesa sidewalls confirming a smooth regrowthinterface. Nevertheless, experimental and simulation resultsreveal that a significant part of the injected current is lostas leakage through the burying material. This is attributed todouble carrier injection into the SI-GaInP:Fe layer.Simulations also predict that the function of GaInP:Fe ascurrent blocking layer should be markedly improved in the caseof GaAs-based longer wavelength lasers. <b>Keywords:</b>semiconductor lasers, in-plane lasers, VCSELs,GaAs, GaInP, semi-insulating materials, hydride vapour phaseepitaxy, regrowth, buried heterostructure, leakage current,simulation.

A new shallow junction formation process, based on selective silicon etching followed by selective growth of in situ B-doped SiGe, is presented. The approach is advantageous compared to conventional ion implantation followed by thermal activation, because perfectly abrupt, low resistivity junctions of arbitrary depth can be obtained. In B-doped SiGe layers, the active doping concentration can exceed the solid solubility in silicon because of strain compensation. In addition, the compressive strain induced in the Si channel can improve drivability through increased hole mobility. The process is integrated by performing the selective etching and the selective SiGe growth in the same reactor. The main advantage of this is that the delicate gate oxide is preserved. The silicon etching process (based on HCl) is shown to be highly selective over SiO2 and anisotropic, exhibiting the densely packed (100), (311) and (111) surfaces. It was found that the process temperature should be confined between 800 ºC, where etch pits occur, and 1000 ºC, where the masking oxide is attacked. B-doped SiGe layers with a resistivity of 5×10-4 Ωcm were obtained. Well-behaved pMOS transistors are presented, yet with low layer quality. Therefore integration issues related to the epitaxial growth, such as selectivity, loading effect, pile-up and defect generation, were investigated. Surface damage originating from reactive-ion etching of the sidewall spacer and nitride residues from LOCOS formation were found to degrade the quality of the SiGe layer. Various remedies are discussed. Nevertheless, high-quality selective epitaxial growth could not be achieved with a doping concentration in the 1021 cm-3 range. The maximum doping level resulting in a high-quality layer, with the loading effect taken into account, was 6×1020 cm-3. After this careful process optimization, a high-quality layer was obtained in the recessed areas. Finally, Ni mono-germanosilicide was investigated as a material for contact formation to the epitaxial SiGe layers in the recessed source and drain areas. The formation temperature is 550 ºC and it is stable up to 700 ºC. The observation of a recessed step and lateral growth of the silicide led to a detailed treatment of the contact resistivity of the NiSi0.8Ge0.2/Si0.8Ge0.2 interface using 2-D as well as 3-D modeling. Different values were obtained for square shaped and rounded contacts, 5.0x10-8 Ωcm2 and 1.4x10-7 Ωcm2, respectively. / QC 20101028

<p>Semiconductor lasers based on gallium arsenide and relatedmaterials are widely used in applications such as opticalcommunication systems, sensing, compact disc players, distancemeasurement, etc. The performance of these lasers can beimproved using a buried heterostructure offering lateralcarrier and optical confinement. In particular, if theconfinement (burying) layer is implemented by epitaxialregrowth of an appropriate aluminium-free semi-insulating (SI)material, passivation of etched surfaces, reduced tendency tooxidation, low capacitance and integration feasibility areadditional advantages.</p><p>The major impediment in the fabrication of GaAs/AlGaAsburied-heterostructure lasers is the spontaneous oxidation ofaluminium on the etched walls of the structure. Al-oxide actsas a mask and makes the regrowth process extremely challenging.In this work, a HCl gas-based<i>in-situ</i>cleaning technique is employed successfully toremove Al-oxide prior to regrowth of SI-GaInP:Fe and SI-GaAs:Fearound Al-containing laser mesas by Hydride Vapour PhaseEpitaxy. Excellent regrowth interfaces, without voids, areobtained, even around AlAs layers. Consequences of usinginadequate cleaning treatments are also presented. Regrowthmorphology aspects are discussed in terms of different growthmechanisms.</p><p>Time-resolved photoluminescence characterisation indicates auniform Fe trap distribution throughout the regrown GaInP:Fe.Scanning capacitance microscopy measurements demonstrate thesemi-insulating nature of the regrown GaInP:Fe layer. Thepresence of EL2 defects in regrown GaAs:Fe makes more difficultthe interpretation of the characterisation results in the nearvicinity of the laser mesa.</p><p>GaAs/AlGaAs buried-heterostructure lasers, both in-planelasers and vertical-cavity surface-emitting lasers, withGaInP:Fe as burying layer are demonstrated for the first time.The lasers exhibit good performance demonstrating thatSI-GaInP:Fe is an appropriate material to be used for thispurpose and the suitability of our cleaning and regrowth methodfor the fabrication of this type of semiconductor lasers.Device characterisation indicates negligible leakage currentalong the etched mesa sidewalls confirming a smooth regrowthinterface. Nevertheless, experimental and simulation resultsreveal that a significant part of the injected current is lostas leakage through the burying material. This is attributed todouble carrier injection into the SI-GaInP:Fe layer.Simulations also predict that the function of GaInP:Fe ascurrent blocking layer should be markedly improved in the caseof GaAs-based longer wavelength lasers.</p><p><b>Keywords:</b>semiconductor lasers, in-plane lasers, VCSELs,GaAs, GaInP, semi-insulating materials, hydride vapour phaseepitaxy, regrowth, buried heterostructure, leakage current,simulation.</p>

<p>A new shallow junction formation process, based on selective silicon etching followed by selective growth of in situ B-doped SiGe, is presented. The approach is advantageous compared to conventional ion implantation followed by thermal activation, because perfectly abrupt, low resistivity junctions of arbitrary depth can be obtained. In B-doped SiGe layers, the active doping concentration can exceed the solid solubility in silicon because of strain compensation. In addition, the compressive strain induced in the Si channel can improve drivability through increased hole mobility. The process is integrated by performing the selective etching and the selective SiGe growth in the same reactor. The main advantage of this is that the delicate gate oxide is preserved. The silicon etching process (based on HCl) is shown to be highly selective over SiO₂ and anisotropic, exhibiting the densely packed (100), (311) and (111) surfaces. It was found that the process temperature should be confined between 800 ºC, where etch pits occur, and 1000 ºC, where the masking oxide is attacked. B-doped SiGe layers with a resistivity of 5×10-⁴ Ωcm were obtained. Well-behaved pMOS transistors are presented, yet with low layer quality. Therefore integration issues related to the epitaxial growth, such as selectivity, loading effect, pile-up and defect generation, were investigated. Surface damage originating from reactive-ion etching of the sidewall spacer and nitride residues from LOCOS formation were found to degrade the quality of the SiGe layer. Various remedies are discussed. Nevertheless, high-quality selective epitaxial growth could not be achieved with a doping concentration in the 1021 cm-3 range. The maximum doping level resulting in a high-quality layer, with the loading effect taken into account, was 6×10²⁰cm-³. After this careful process optimization, a high-quality layer was obtained in the recessed areas. Finally, Ni mono-germanosilicide was investigated as a material for contact formation to the epitaxial SiGe layers in the recessed source and drain areas. The formation temperature is 550 ºC and it is stable up to 700 ºC. The observation of a recessed step and lateral growth of the silicide led to a detailed treatment of the contact resistivity of the NiSi₀.₈Ge_0.2/Si_0.8Ge_0.2 interface using 2-D as well as 3-D modeling. Different values were obtained for square shaped and rounded contacts, 5.0x10^-8 Ωcm² and 1.4x10^-7 Ωcm², respectively.</p>

Die vorliegende Arbeit befasst sich mit dem Einfluss der elektrischen Polarisation auf Eigenschaften freier Träger in ZnO basierten Halbleiterheterostrukturen. Dabei werden insbesondere Transporteigenschaften freier Träger sowie deren Rekombinationsdynamik untersucht. Die Arbeit behandelt vier inhaltliche Schwerpunkte. Der erste Schwerpunkt liegt auf den physikalischen Eigenschaften der verwendeten Materialen, hier wird der Zusammenhang der Bandlücke und der Gitterkonstanten von MgZnO Dünnfilmen und deren Magnesiumgehalt beschrieben. Weiterhin wird die Morphologie solcher Filme diskutiert. Auf unterschiedliche Substrate und Abscheidebedingungen wird dabei detailliert eingegangen. Der zweite Schwerpunkt behandelt die Eigenschaften undotierter und phosphordotierter ZnO und MgZnO Dünnfilme. Die strukturellen, Transport- und Lumineszenzeigenschaften werden hier verglichen und Rückschlüsse auf die Züchtungsbedingungen gezogen. Im dritten Schwerpunkt werden Quanteneffekte an ZnO/MgZnO Grenzflaechen behandelt. Hierbei wird insbesondere auf den Einfluss der elektrischen Polarisation eingegangen. Die Präsenz eines zweidimensionalen Elektronengases wird nachgewiesen, und die notwendigen Bedingungen zur Entstehung des sogenannten qunatum confined Stark-effects werden dargelegt. Insbesondere wird hier auf züchtungsrelevante Parameter eingegangen. Den vierten Schwerpunkt stellen Kopplungsphänomene in ZnO/BaTiO3 Heterostrukturen dar. Dabei werden zuerst die experimentell beobachten Eigenschaften verschiedener Heterostrukturen die auf unterschiedlichen Substraten gezüchtet wurden aufgezeigt. Hier stehen strukturelle und Transporteigenschaften im Vordergrund. Ein Modell zur Beschreibung der Ausbildung von Raumladungszonen in derartigen Heterostrukturen wird eingeführt und zur Beschreibung der experimentellen Ergebnisse angewandt. Die Nutzbarkeit der ferroelektrischen Eigenschaften des Materials BaTiO3 in Kombination mit halbleitendem ZnO wurden untersucht. Hierzu wurden ferroelektrische Feldeffekttransistoren unter Verwendung beider Materialien hergestellt. Die prinzipielle Eignung der Bauelemente als nichtflüchtige Speicherelemente wurde nachgewiesen.

Heterostructures of materials with dramatically different properties are exciting for a variety of devices. In particular, the epitaxial integration of metals with semiconductors is promising for low-loss tunnel junctions, embedded Ohmic contacts, high-conductivity spreading layers, as well as optical devices based on the surface plasmons at metal/semiconductor interfaces. This thesis investigates the structural, electrical, and optical properties of compound (III-V) semiconductors employing rare-earth monopnictide (RE-V) nanostructures. Tunnel junctions employing RE-V nanoparticles are developed to enhance current optical devices, and the epitaxial incorporation of RE-V films is discussed for embedded electrical and plasmonic devices. Leveraging the favorable band alignments of RE-V materials in GaAs and GaSb semiconductors, nanoparticle-enhanced tunnel junctions are investigated for applications of wide-bandgap tunnel junctions and lightly-doped tunnel junctions in optical devices. Through optimization of the growth space, ErAs nanoparticle-enhanced GaAs tunnel junctions exhibit conductivity similar to the best reports on the material system. Additionally, GaSb-based tunnel junctions are developed with low p-type doping that could reduce optical loss in the cladding of a 4 μm laser by ~75%. These tunnel junctions have several advantages over competing approaches, including improved thermal stability, precise control over nanoparticle location, and incorporation of a manifold of states at the tunnel junction interface. Investigating the integration of RE-V nanostructures into optical devices revealed important details of the RE-V growth, allowing for quantum wells to be grown within 15nm of an ErAs nanoparticle layer with minimal degradation (i.e. 95% of the peak photoluminescence intensity). This investigation into the MBE growth of ErAs provides the foundation for enhancing optical devices with RE-V nanostructures. Additionally, the improved understanding of ErAs growth leads to development of a method to grow full films of RE-V embedded in III-V materials. The growth method overcomes the mismatch in rotational symmetry of RE-V and III-V materials by seeding film growth with epitaxial nanoparticles, and growing the film through a thin III-V spacer. The growth of RE-V films is promising for both embedded electrical devices as well as a potential path towards realization of plasmonic devices with epitaxially integrated metallic films. / text