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S ; 119081 119083 99 ; S ; S ; S ; Copyright (2011) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. We perform Raman-scattering measurements at high hydrostatic pressures on c-face and a-face InN layers to investigate the high-pressure behavior of the zone-center optical phonons of wurtzite InN. Linear pressure coefficients and mode Grneisen parameters are obtained, and the experimental results are compared with theoretical values obtained from ab initio lattice-dynamical calculations. Good agreement is found between the experimental and calculated results. © 2011 American Institute of Physics. Work supported by the Spanish MICINN (Projects MAT2010-16116, MAT2008-06873-C02-02, MAT2010-21270-C04-04, and CSD2007-00045), the Catalan Government (BE-DG 2009), and the Spanish Council for Research (PIE2009-CSIC). Ibanez, J.; Manjón Herrera, FJ.; Segura, A.; Oliva, R.; Cusco, R.; Vilaplana Cerda, RI.; Yamaguchi, T. (2011). High-pressure Raman scattering in wurtzite indium nitride. Applied Physics Letters. 99:119081-119083. https://doi.org/10.1063/1.3609327 Veal, T., McConville, C., & Schaff, W. (Eds.). (2009). Indium Nitride and Related Alloys. doi:10.1201/9781420078107 Gallinat, C. S., Koblmüller, G., Brown, J. S., Bernardis, S., Speck, J. S., Chern, G. D., … Wraback, M. (2006). In-polar InN grown by plasma-assisted molecular beam epitaxy. Applied Physics Letters, 89(3), 032109. doi:10.1063/1.2234274 Li, S. X., Wu, J., Haller, E. E., Walukiewicz, W., Shan, W., Lu, H., & Schaff, W. J. (2003). Hydrostatic pressure dependence of the fundamental bandgap of InN and In-rich group III nitride alloys. Applied Physics Letters, 83(24), 4963-4965. doi:10.1063/1.1633681 Gorczyca, I., Plesiewicz, J., Dmowski, L., Suski, T., Christensen, N. E., Svane, A., … Speck, J. S. (2008). Electronic structure and effective masses of InN under pressure. Journal of Applied Physics, 104(1), 013704. ...

Copyright (2011) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. ; We perform Raman-scattering measurements at high hydrostatic pressures on c-face and a-face InN layers to investigate the high-pressure behavior of the zone-center optical phonons of wurtzite InN. Linear pressure coefficients and mode Grneisen parameters are obtained, and the experimental results are compared with theoretical values obtained from ab initio lattice-dynamical calculations. Good agreement is found between the experimental and calculated results. © 2011 American Institute of Physics. ; Work supported by the Spanish MICINN (Projects MAT2010-16116, MAT2008-06873-C02-02, MAT2010-21270-C04-04, and CSD2007-00045), the Catalan Government (BE-DG 2009), and the Spanish Council for Research (PIE2009-CSIC). ; Ibanez, J.; Manjón Herrera, FJ.; Segura, A.; Oliva, R.; Cusco, R.; Vilaplana Cerda, RI.; Yamaguchi, T. (2011). High-pressure Raman scattering in wurtzite indium nitride. Applied Physics Letters. 99:119081-119083. https://doi.org/10.1063/1.3609327 ; S ; 119081 ; 119083 ; 99 ; Veal, T., McConville, C., & Schaff, W. (Eds.). (2009). Indium Nitride and Related Alloys. doi:10.1201/9781420078107 ; Gallinat, C. S., Koblmüller, G., Brown, J. S., Bernardis, S., Speck, J. S., Chern, G. D., … Wraback, M. (2006). In-polar InN grown by plasma-assisted molecular beam epitaxy. Applied Physics Letters, 89(3), 032109. doi:10.1063/1.2234274 ; Li, S. X., Wu, J., Haller, E. E., Walukiewicz, W., Shan, W., Lu, H., & Schaff, W. J. (2003). Hydrostatic pressure dependence of the fundamental bandgap of InN and In-rich group III nitride alloys. Applied Physics Letters, 83(24), 4963-4965. doi:10.1063/1.1633681 ; Gorczyca, I., Plesiewicz, J., Dmowski, L., Suski, T., Christensen, N. E., Svane, A., … Speck, J. S. (2008). Electronic structure and effective masses of InN under pressure. Journal of Applied Physics, 104(1), 013704. ...

Tris-N,N,-dimethyl-N,N -diisopropylguanidinatoindium(III) has been investigated both as a chemical vapor deposition precursor and an atomic layer deposition precursor. Although deposition was satisfactory in both cases, each report showed some anomalies in the thermal stability of this compound, warrenting further investigation, which is reported herein. The compound was found to decompose to produce diisopropylcarbodiimide both by computational modeling and solution phase nuclear magnetic resonance characterization. The decomposition was shown to have an onset at approximately 120 degrees C and had a constant rate of decomposition from 150 to 180 degrees C. The ultimate decomposition product was suspected to be bisdimethylamidoN, N,-dimethyl-N,N -diisopropylguanidinato-indium(III), which appeared to be an intractable, nonvolatile polymer. Published by the AVS. ; Funding Agencies|Swedish foundation for Strategic Research through the project "Time-resolved low temperature CVD for III-nitrides" [SSF-RMA15-0018]; COST Action [MP1402]; COST (European Cooperation in Science and Technology); Vinnova VINNMER Marie Curie incoming mobility program (Vinnova Grant) [2015-03714]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO Mat LiU) [2009 00971]; Swedish Research Council (VR Grant) [2016-05137_4]; Wenner-Gren foundations

Indium nitride (InN) is characterized by its high electron mobility, making it a ground-breaking material for high frequency electronics. The difficulty of depositing high-quality crystalline InN currently impedes its broad implementation in electronic devices. Herein, we report a new highly volatile In(III) triazenide precursor and demonstrate its ability to deposit high-quality epitaxial hexagonal InN by atomic layer deposition (ALD). The new In(III) precursor, the first example of a homoleptic triazenide used in a vapor deposition process, was easily synthesized and purified by sublimation. Thermogravimetric analysis showed single step volatilization with an onset temperature of 145 degrees C and negligible residual mass. Strikingly, two temperature intervals with self-limiting growth were observed when depositing InN films. In the high-temperature interval, the precursor underwent a gas-phase thermal decomposition inside the ALD reaction chamber to produce a more reactive In(III) compound while retaining self-limiting growth behavior. Density functional theory calculations revealed a unique two-step decomposition process, which liberates three molecules of each propene and N-2 to give a smaller tricoordinated In(III) species. Stoichiometric InN films with very low levels of impurities were grown epitaxially on 4H-SiC. The InN films deposited at 325 degrees C had a sheet resistivity of 920 Omega/sq. This new triazenide precursor enables ALD of InN for semiconductor applications and provides a new family of M-N bonded precursors for future deposition processes. ; Funding Agencies|Swedish foundation for Strategic Research through the project "Time-resolved low temperature CVD for III-nitrides" [SSF-RMA 15-0018]; Knut and Alice Wallenberg foundation through the project "Bridging the THz gap" [KAW 2013.0049]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO Mat LiU) [2009 00971]

Plasmonic response of free charges confined in nanostructures of plasmonic materials is a powerful means for manipulating the light-material interaction at the nanoscale and hence has influence on various relevant technologies. In particular, plasmonic materials responsive in the mid-infrared range are technologically important as the mid-infrared is home to the vibrational resonance of molecules and also thermal radiation of hot objects. However, the development of the field is practically challenged with the lack of low-loss materials supporting high quality plasmons in this range of the spectrum. Here, we demonstrate that degenerately doped InN nanocrystals (NCs) support tunable and low-loss plasmon resonance spanning the entire midwave infrared range. Modulating free-carrier concentration is achieved by engineering nitrogen-vacancy defects (InN1-x, 0.017 amp;lt; x amp;lt; 0.085) in highly degenerate NCs using a nonequilibrium gas-phase growth process. Despite the significant reduction in the carrier mobility relative to intrinsic InN, the mobility in degenerate InN NCs (amp;gt;60 cm(2)/(V s)) remains considerably higher than the carrier mobility reported for other materials NCs such as doped metal oxides, chalcogenides, and noble metals. These findings demonstrate feasibility of controlled tuning of infrared plasmon resonances in a low-loss material of III-V compounds and open a gateway to further studies of these materials nanostructures for infrared plasmonic applications. ; Funding Agencies|Knut and Alice Wallenberg Foundation [KAW 14.0276]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (faculty Grant SFO-Mat-LiU) [2009-00971]; EPSRC [EP/M024938/1]

Group III-Nitride semiconductors: indium nitride (InN), gallium nitride (GaN), aluminum nitride (AlN) and their alloys continue to attract significant scientific interest due to their unique properties and diverse applications in photonic and electronic applications. Group-III nitrides have direct bandgaps which cover the entire spectral range from the infrared (InN) to the ultraviolet (GaN) and to the deep ultraviolet (AlN). This makes III-nitride materials suitable for high-efficient and energy-saving optoelectronic devices, such as light-emitting diodes (LEDs) and laser diodes (LDs). The Nobel Prize in Physics 2014 was awarded for the invention of efficient GaN blue LEDs, which further accelerated the research in the field of group III-nitride materials. GaN and related alloys are also suitable for high-temperature, high-power and high-frequency electronic devices with performance that cannot be delivered by other semiconductor technologies such as silicon (Si) and gallium arsenide (GaAs). For example, GaN-based high electron mobility transistors (HEMTs) have been widely adopted for radio frequency (RF) communication and power amplifiers, high-voltage power switches in radars, satellites, and wireless base stations for 5G. Recently, nitrogen (N)-polar group-III nitrides have drawn much attention due to their advantages over their metal-polar counterparts in e.g. HEMTs. These include feasibility to fabricate ohmic contacts with low resistance, an enhanced carrier confinement with a natural back barrier, and improved device scalability. Despite intensive research, the growth of micrometer-thick high-quality N-polar GaN based materials remains challenging. One of the major problems to develop device-quality N-polar nitrides is the high surface roughness, which results from the formation of hexagonal hillocks or step-bunching. Another significant hurdle is the unintentional polarity inversion, which reduces the crystalline quality and prohibits device fabrication. This licentiate thesis focuses on the development of N-polar AlN and GaN heterostructures on SiC substrates for HEMT RF applications. The overall aim is to exploit the advantages of the hot-wall MOCVD concept to grow high-quality N-polar HEMT structures for higher operational frequencies and improved device performance. In order to achieve this goal, special effort is dedicated to understanding the effects of growth conditions and substrate orientation on the structural properties and polarity of AlN, GaN and AlGaN grown by hot-wall MOCVD. N-polar AlN nucleation layers (NLs) with layer by layer growth mode and step-flow growth mode can be achieved on on-axis and 4_ offaxis SiC (000¯1), respectively, by carefully controlling V/III ratio and growth temperature. Utilizing scanning transmission electron microscopy (STEM) we have established a comprehensive picture of the atomic arrangements, local polarity and polarity evolution in AlN, GaN/AlN and AlGaN/GaN/AlN in the cases of low-temperature and high-temperature AlN NLs both for on-axis and off-axis substrates. We have shown that typically employed methods for polarity determination using potassium hydroxide wet etching could not provide conclusive results in the case of mixed-polar AlN as Al-polar domains may be easily over-etched and remain undetected. Atomic scale electron microscopy is therefore needed to accurately determine the polarity. We further have developed growth strategy and have optimized the epitaxial process for N-polar GaN, and have demonstrated high quality N-polar AlGaN/GaN/AlN heterostructures. ; Additional funding agencies: Chalmers University of technology; ABB; Ericsson; Epiluvac; FMV; Gotmic; Saab; SweGaN; UMS; Swedish Foundation for Strategic Research under Grants No. FL12-0181, No. RIF14-055, and No. EM16-0024; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University, Faculty Grant SFO Mat LiU No.2009- 00971.

Indium nitride (InN) is an interesting material for future high-frequency electronics due to its high electron mobility. The problematic deposition of InN films currently prevents full exploration of InN-based electronics. We present studies of atomic layer deposition (ALD) of InN using In precursors with bidentate ligands forming In-N bonds: tris(N,N-dimethyl-N,N -diisopropylguanidinato)indium(III), tris(N,N-diisopropylamidinato)indium(III), and tris(N,N-diisopropylformamidinato)indium(III). These compounds form a series were the size of the substituent on the endocyclic position decreases from -NMe2 to -Me and to -H, respectively. We show that when the size of the substituent decreases, the InN films deposited have a better crystalline quality, of better optical quality, lower roughness, and an In/N ratio closer to unity. From quantum chemical calculations, we show that the smaller substituents lead to less steric repulsion and weaker bonds between the ligand and In center. We propose that these effects render a more favored surface chemistry for the nitridation step in the ALD cycle, which explains the improved film properties. ; Funding Agencies|Swedish foundation for Strategic Research through the project "Time-resolved low temperature CVD for III-nitrides" [SSF-RMA 15-0018]; Knut and Alice Wallenberg foundation through the project "Bridging the THz gap" [KAW 2013.0049]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO Mat LiU) [2009 00971]

Aluminum nitride (AlN), gallium nitride (GaN),and indium nitride (InN) form a family of technologicallyimportant semiconductors of high importance to light-emittingdiodes and high-frequency electronics. Although thinfilms of thesematerials are routinely manufactured by chemical vapor deposition(CVD) and atomic layer deposition (ALD), these methods are farfrom optimal and knowledge of the underlying chemical processesis lacking. In this work, we performed ab initio investigations of thesurface coverage of these materials under an ammonia-richatmosphere. Periodic density functional theory calculations wereused to test the probable surface structures, and their electronicand thermal energies were used to calculate their contribution tothe surface composition under the temperature and pressureconditions relevant for CVD and ALD processes of these materials. The results show similarities between the group of materials witha similar NHxsurface structure present for all three. Comparison of the coverage showed that at low growth temperatures, thesurface is expected to be covered by NH2, while at high temperatures, most surface sites would be vacant. The surface structureswere all found to be the most stable on AlN and least stable on InN. These results are important for further investigations of thematerial growth mechanisms. ; Funding Agencies|Swedish foundation for Strategic Research through the project "Time-resolved low temperature CVD for III-nitrides" [SSF-RMA 15-0018]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at the Linkoping University (Faculty Grant SFO Mat LiU) [2009 00971]; Swedish Research Council (VR)Swedish Research Council

Recommendations for conducting ecological evaluation of nanomaterials are prepared. It is necessary to exercise control in order to establish effect of nanoproducts on the environment and human health for safe and productive use of nanotechnology. A general procedure for the system of nanosafety and certification of nanoindustry product should be based on creating standardizing, legislative and methodological support of safety system in the process of production, handling and disposal of nanomaterials. It was found that in order to perform assessment, nanoproducts should be examined at all stages of the life cycle. A scheme of the life cycle of nanomaterials was developed, which should be considered as a multi-stage process from the preparation of the source material to the reclamation. According to the methods proposed and recommendations developed, ecological assessment of porous indium phosphide and the device based on it, indium nitride, was performed. Nanostructures are investigated using the methods of scanning electronic microscopy, chemical analysis, the method of average projected diameter, gravimetric method, etc. It was found that porous indium phosphide may be health hazardous. Porous indium phosphide is formed by the method of electrochemical etching in the solutions of acids. Such methods of synthesis of nanostructures pose an ecological threat. Understanding these threats will optimize the processes of formation and operation of nanomaterials for ecological safety and will highlight the key moments of safe usage and disposal of products of nanotechnology. ; Разработаны рекомендации для проведения экологической экспертизы наноматериалов. Установлено, что для проведения экспертизы нанопродукты следует исследовать на всех стадиях жизненного цикла. Разработана схема жизненного цикла наноматериалов, которая представляет собой многостадийный процесс от подготовки исходного материала до утилизации. Проведена экологическая оценка пористого фосфида индия и устройства на его основе – нитрида индия ; Розроблено рекомендації для проведення екологічної експертизи наноматеріалів. Встановлено, що для проведення експертизи нанопродукти слід досліджувати на всіх стадіях життєвого циклу. Розроблено схему життєвого циклу наноматеріалів, що представляє собою багатостадійний процес від підготовки вихідного матеріалу до утилізації. Проведено екологічну оцінку поруватого фосфіду індію та приладу на його основі – нітриду індію

Group-III nitride materials, gallium nitride (GaN), aluminum nitride (AlN) and indium nitride (InN) have direct band gaps with band gap energies ranging from the infrared (InN) to the ultraviolet (GaN) and to the deep ultraviolet (AlN) wavelengths and covering the entire spectral range from 0.7 eV to 6.2 eV upon alloying. The invention of the GaN-based blue LEDs, for which the Nobel prize in Physics was awarded in 2014, has opened up avenues for exploration of IIINitride material and device technologies and has inspired generations of researchers in the semiconductor field. Group-III nitrides have also been demonstrated to be among the most promising semiconductors for next generation of efficient high-power, high-temperature and high-frequency electronic devices. The need to build a sustainable and efficient energy system motivates the development of vertical GaN transistors and diodes for applications with power ratings of 50-150 kW, e.g., in electric vehicles and industrial inverters. The key is to grow GaN layers with low concentration of defects (impurities and dislocations), which enables an expansion in both voltage and current ratings and reduction of cost. Despite intense investigations and impressive advances in the field, defects are still a major problem hindering exploiting the full potential of GaN in power electronics. This Licentiate thesis focuses on the development of two different epitaxial approaches in MOCVD for reducing dislocation densities in GaN with controlled doping for power device applications: i) growth of planar GaN layers trough NWs reformation, which can be further exploited as templates for a subsequent growth of thick drift layers and ii) homoepitaxial GaN growth. Special attention is put on understanding homoepitaxial growth under different nucleation schemes and thermal stability of GaN. We have established conditions in homoepitaxy to deliver state-of-the-art GaN material with low impurity levels combined with a reasonable growth rate suitable for growth of thick drift layers. The results are summarized in two papers: In Paper I we investigate GaN layers with different thicknesses on reformed GaN NW templates and highlight this approach as an alternative to the expensive GaN HVPE substrates. The sapphire used as a substrate limits to some extent the reduction of threading dislocations, however, the resulting GaN material presents smooth surfaces and thermal conductivity close to the bulk value, which suggests the potential of this approach to be integrated in GaN development as an active material for power devices on various substrates. In Paper II extensive study of homoepitaxial GaN growth by hot-wall MOCVD is presented together with results on the thermal stability of GaN under typical conditions used in our growth reactor. Understanding the evolution of GaN surface under different gas compositions and temperatures allows us to predict optimum homoepitaxial conditions. Analysis in the framework of Ga supersaturation of epilayers simultaneously grown on GaN templates and on GaN HVPE substrates reveals that residual strain and screw dislocation densities affect GaN nucleation and growth and lead to distinctively different morphologies on GaN templates and native substrates, respectively. The established comprehensive picture provides guidance for designing strategies for growth conditions optimization in homoepitaxy. We demonstrate homoepitaxial GaN-on-GaN grown under optimum growth conditions with state-of-the-art smooth surface with an rms value of 0.021 nm and an average TDD of 1.4·106 cm-2 which provide good basis for augmenting power device structures.Future work will be focused on GaN NWs reformation on different substrates, p- and n-type doping of homoepitaxial GaN with impurity control and the fabrication of pn power diode device structures for further processing and assessment by C3NiT partners. ; Funding agencies: The Swedish Research Council (VR) under Grant No. 2016-00889, The Swedish Governmental Agency for Innovation Systems (VINNOVA) under the Competence Center Program, Grant No. 2016-05190, The Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University, Faculty Grant SFO Mat LiU No.2009-00971, The Swedish Foundation for Strategic Research (SSF), under Grant No. EM16-0024

The widespread implementation of white light-emitting diodes (wLEDs), based on the blue electroluminescence of an LED and the yellow photoluminescence of a phosphor, represents a major opportunity to reduce global energy consumption. The performances of wLEDs are based on materials considered as critical, such as gallium and gallium/indium nitrides for the blue LED, and cerium doped yttrium aluminium garnet for the phosphor. The synthesis of these materials require costly and high-temperature physical and chemical deposition techniques. In this context, new non-critical materials have been studied and manufactured by soft chemistry methods: ZnO nanowires array as n-type semiconductor, and aluminoborate powders as phosphor. On the one hand, the mechanisms of the extrinsic doping and related modification of the growth of ZnO nanowires deposited by chemical bath deposition were investigated, showing the dominant roles of pH and precursor concentrations. Defects and complex defects incorporated in ZnO nanowires, crucial from an application point of view, greatly modify their optical and electrical proprieties. Their epitaxial growth on p-type GaN thin films forms heterojunctions whose electroluminescence properties are evaluated. On the other hand, aluminoborate-based phosphors powders were synthesized by the Pechini method, by substituting yttrium, usually present in the amorphous particles. The optimization of the new chemical compositions and thermal annealing offers a broad emission whose internal quantum luminescence efficiency exceeds 60 %. This study provides a better understanding of the trapping of carbon species, and their role in the luminescence. Eventually, consumer interest in such structures without critical materials and with low embodied energy is measured and offers optimistic prospects for their development. ; L'implémentation généralisée de diodes électroluminescentes blanches (wLED), basées sur l'électroluminescence bleue d'une LED et la photoluminescence jaune d'un luminophore, représente une opportunité majeure de réduction de la consommation énergétique mondiale. Les performances des wLED reposent sur des matériaux considérés comme critiques par les mondes politiques et scientifiques, comme les nitrures de gallium et de gallium/indium pour la LED bleue, et le grenat d'yttrium et d'aluminium dopé au cérium pour le luminophore. La synthèse de ces matériaux nécessite des techniques de dépôt physique et chimique coûteuses et à haute température. C'est dans ce contexte qu'ont été étudiés deux matériaux non critiques et fabriqués par des méthodes de chimie douce : les réseaux de nanofils de ZnO comme semi-conducteurs de type n, et les poudres d'aluminoborate comme luminophore. D'une part, les mécanismes de dopage extrinsèque et la modification associée de la croissance des nanofils de ZnO par dépôt en bain chimique ont été examinés, montrant les rôles dominants du pH et de la concentration en précurseurs. Les défauts et complexes de défauts incorporés au sein des nanofils de ZnO, cruciaux du point de vue applicatif, modifient largement leurs propriétés optiques et électriques. Leur croissance épitaxiale sur des couches minces de GaN de type p forme des hétérojonctions dont les propriétés d'électroluminescence sont évaluées. D'autre part, les poudres luminophores à base d'aluminoborate ont été synthétisées par la méthode Pechini, en substituant l'yttrium habituellement présent dans les particules amorphes. L'optimisation des nouvelles compositions chimiques et des traitements thermiques offre une émission spectrale large, dont le rendement quantique interne de luminescence dépasse 60 %. Cette étude permet une meilleure compréhension du piégeage d'espèces carbonées, et de leur rôle dans la luminescence. Finalement, l'intérêt des consommateurs pour de telles structures sans matériaux critiques et à basse énergie grise est mesuré et offre des perspectives optimistes pour leur développement.

The devolopment of group-III nitride semiconductor technology continues to expand rapidly over the last two decades. The indium nitride (InN), gallium nitride (GaN) and aluminum nitride (AlN) compounds and their alloys are direct bandgap semiconductors with a wide bandgap range, spanning from infrared(IR) to deep-ultraviolet (UV), enabling their utilization in optoelectronic industry. The GaN-based light-emitting diode (LED) is already the commercial solution for efficient and energy saving lighting. Additionally, the physical properties of these materials such as the high critical electric field, the high saturation carrier velocity and the high thermal conductivity, make them promising candidates for replacing silicon (Si), and other wide-bandgap semiconductors such as silicon carbide (SiC) in power devices. More importantly, the polarization-induced two-dimensional electron gas (2DEG), forming at the interfaces of these semiconductors, led to the fabrication of the GaN-based high electron mobility transistor (HEMT). This device is suitable for high power (HP) switching, power amplifiers and high frequency (HF) applications in the millimeter-wave range up to THz frequencies. As such, HEMTs are suitable for 5G communication systems, radars, satellites and a plethora of other related applications. Achieving the efficient GaN blue LED (Nobel Prize in Physics 2014), came as a result of (partially) solving several material issues of which, p-type GaN was of crucial importance. Since 1992, a lot of effort is being dedicated on the understanding and overcoming of the limitations hindering efficient p-type conductivity and low hole mobility in metal-organic chemical vapor deposition (MOCVD) grown p-GaN. The limitations arise from the fact that magnesium (Mg) is the only efficient p-type dopant for GaN so far and only a very small percentage ∼2% of the incorporated Mg is active at room temperature. More limitations come from its solubility in GaN and the crystal quality deterioration and formation of inversion domains (IDs) at high doping levels. Free-hole concentrations in the low 1018 cm-3 range with mobilities at ∼10 cm2V-1s-1 demonstrate the state-of-art in MOCVD grown p-GaN, still leaving a wide window for improvement. Another intensively investigated topic is related to the aluminum gallium nitride (AlGaN)/GaN HEMTs. High electron density and mobility of the 2DEG in the range of 1013 cm-2 and ∼2400 cm2V-1s-1 respectively, are reported. Interface engineering, addition of interlayers and backbarriers are only some of the modifications introduced at the basic AlGaN/GaN HEMT structure in order to achieve the aforementioned values. Nevertheless, fundamental phenomena can still be revealed by special characterization techniques and provide a deeper understanding on the causal factors of theHEMT's macroscopic properties. The main research results presented in this licentiate thesis are organized in three papers: In paper I we perform an in-depth investigation of the Mg-doped GaN growth by hot-wall MOCVD. We strive for exploiting any possible advantages of the hot-wall MOCVD on the growth of high-quality p-GaN relevant for use in HP devices. Additionally, we aim to gain a comprehensive understanding of the growth process and its limiting factors. The effects of growth conditions on the Mg, hydrogen (H) and carbon (C) incorporation in GaN are approached from the gallium (Ga)-supersaturation point of view. Control of the bis(cyclopentadienyl) magnesium (Cp2Mg)/trimethylgallium(TMGa) ratio, the V/III ratio and the growth temperature, resulted in high quality p-GaN growth on AlN/4H-SiC templates, showing state-of-the-art electrical properties. In paper II, we manage to increase the free-hole concentrations in as-grown GaN:Mg in two different ways, either by growing the GaN:Mg layer on a GaN/AlN/4H-SiC template, or by modifying the gas environment of the growth. It is shown that using a GaN/AlN/4H-SiC template results in higher carrier concentration and large improvement of the as-grown p-GaN resistivity. More importantly, the high amount of hydrogen (H2) flow during GaN:Mg growth, results in higher amount of non-passivated Mg in the as-grown layers allowing for high free-hole concentration and significantly lower resistivity in the as-grown p-GaN. Paper III focuses on the effect of aluminum (Al)-content variation in the barrier layer of AlGaN/GaN HEMTs. The THz-optical Hall effect (OHE) measurements revealed a peak of the 2DEG mobility followed by a decrease above certain value of Al%. We correlate this effect with the electron effective mass (meff) variation and draw conclusions about the mobility limiting mechanisms. In the low-Al regime, the mobility decreases because of the increase in meff while, in the high-Al regime, the mobility is limited by the lower carrier scattering time. ; Funding agencies: The Swedish Governmental Agency for Innovation Systems (VINNOVA) under the Competence Center Program Grant No.2016−05190, Linköping University, Chalmers University of technology, Ericsson, Epiluvac, FMV, Gotmic, Hexagem, Hitachi Energy, On Semiconductor, Saab, SweGaN, UMS, the Swedish Research Council VR under Award No. 2016 − 00889, the Swedish Foundation for Strategic Research under Grants No. RIF14 − 055 and No. EM16 − 0024, and the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University, Faculty Grant SFO Mat LiU No.2009 − 00971.

The influence of structural configurations of indium aluminum nitride (InA1N) nanospirals, grown by reactive magnetron sputter epitaxy, on the transformation of light polarization are investigated in terms of varying structural chirality, growth temperatures, titanium nitride (TiN) seed (buffer) layer thickness, nanospiral thickness, and pitch. The handedness of reflected circularly polarized light in the ultraviolet-visible region corresponding to the chirality of nanospirals is demonstrated. A high degree of circular polarization (P-c) value of 0.75 is obtained from a sample consisting of 1.2 mu m InA1N nanospirals grown at 650 degrees C. A film-like structure is formed at temperatures lower than 450 degrees C. At growth temperatures higher than 750 degrees C, less than 0.1 In-content is incorporated into the InA1N nanospirals. Both cases reveal very low P-c-A red shift of wavelength at P-c peak is found with increasing nanospiral pitch in the range of 200-300 nm. The P-c decreases to 0.37 for two-turn nanospirals with total length of 0.7 mu m, attributed to insufficient constructive interference. A branch-like structure appears on the surface when the nanospirals are grown longer than 1.2 mu m, which yields a low P-c around 0.5, caused by the excessive scattering of incident light. ; Funding Agencies|Swedish Research Council (VR) [621-2012-4420, 621-2013-5360, 621-2013-4018]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [SFO-Mat-LiU 2009-00971]; Centre in Nano science and technology (CeNano) at Linkoping University

The demand for environment-friendly energy sources increases more and more, which is not only caused by the energy turnaround initialized by the Federal Government. In this context, the focus is set mainly on the development of wind power and solar energy with competitive production costs. Above all, this is a problem for solar cells, which, today, are mainly fabricated out of crystalline silicon and, therefore, are in competition with semiconductor industry. Hence, the development of solar cells based on alternative materials like e.g. copper-indium-gallium-diselenide (CIGS) is of great interest. Because of the lower layer thickness needed for this material, these solar cells can be fabricated on flexible substrates like metal foils. This possibility offers a broader spectrum of applications. For reaching low production costs, the applicability of unpolished steel foil, which exhibits scratches on the µm scale, is investigated as substrate for the solar cells in this work. The use of any metal as substrate requires a barrier layer between the substrate and the solar cells to prevent short-circuits between the separate cells of a solar module and to prevent the diffusion of undesired substrate elements into the solar cells. In this work, siliconoxide and silicon-nitride coatings are deposited as barrier layers in a microwaveplasma process in a gas mixture of HMDSO (hexamethyldisiloxane) and oxygen or monosilane and ammonia. To have the opportunity of influencing the layer growth by high-energetic ions, an additional substrate bias is applied during the deposition, which leads to a capacitive discharge superimposing the microwave one. The high-energetic ions impinging on the layer surface lead to a layer smoothing and melting, especially at positions of indentations in the substrate surface. Hence, the barrier properties of the coating are improved clearly, which was identified by insulation measurements of the deposited film. The layer growth modification is analyzed on the basis of substrates with a well-defined rough surface structure in the µm range experimentally as well as by simulations with the Monte-Carlo Code SDTrimSP-2D, which allows a detailed analysis of the local layer growth mechanisms contributing to the deposition. Additionally, the impinge of the energetic ions affects the molecular structure and composition of the coatings as well. These parameters are an important indicator for the layer material properties like adhesion, hardness and diffusion properties. The molecular composition of the deposited layers is analyzed in detail by Fourier- ransform infrared (FTIR) spectroscopy. From the layer composition and their refractive index, conclusions on the diffusion behavior of the coatings are drawn. In case of applying the substrate bias, the spectra indicate a denser and harder film in case of silicon oxide. Hence, these layers are more diffusion preventing compared to the unbiased ones. On the other hand, the silicon-nitride coatings show contrary properties: They offer more porous layers, when the substrate bias is applied, and, therefore, they assist diffusion. ; Nicht erst seit der von der Bundesregierung initiierten Energiewende besteht eine große Nachfrage nach umweltverträglichen Energiequellen. Dabei ist eines der Hauptaugenmerke die Entwicklung von Solarzellen mit wettbewerbsfähigen Herstellungskosten, da die Solarzellen heutzutage hauptsächlich aus kristallinem Silizium bestehen und folglich deren Produktion in Konkurrenz zur Halbleiterindustrie steht. Somit ist die Entwicklung von Solarzellen aus alternativen Materialien wie z.B. Kupfer-Indium-Gallium-Diselenid (CIGS) von großem Interesse. Da von diesem Material eine geringere Schichtdicke benötigt wird, können diese Solarzellen auf flexiblen Substraten wie auf einer Metallfolie hergestellt werden, was eine breitere Anwendung ermöglicht. In dieser Arbeit wird die Eignung von unpolierter Stahlfolie, die Kratzer im µm-Bereich aufweist, als Träger für die Solarzellen untersucht. Die Verwendung von Metallsubstraten erfordert eine Barriere zwischen dem Substrat und den Solarzellen, um Kurzschlüsse zwischen den einzelnen Zellen eines Solarmoduls zu vermeiden. Außerdem soll durch diese Barriere die Diffusion unerwünschter Substratbestandteile in die Solarzellen verhindert werden. Hierzu werden in dieser Arbeit Siliziumoxid- und Siliziumnitridschichten in einem Mikrowellen-Plasma-Prozess in einem Gasgemisch von HMDSO (Hexamethyldisiloxan) und Sauerstoff bzw. Monosilan und Ammoniak abgeschieden. Um das Schichtwachstum durch hochenergetische Ionen beeinflussen zu können, wird der Einfluss eines zusätzlichen Substratbias untersucht, was zu einer Überlagerung einer kapazitiven Entladung und der Mikrowellenentladung führt. Die auf der Schichtoberfläche auftreffenden energiereichen Ionen führen zu einer Glättung und Verschmelzung der Oberfläche, besonders bei Unebenheiten auf der Substratoberfläche. Somit verbessern sich die Barriereeigenschaften der Schicht deutlich, was mittels Isolationsmessungen ermittelt wurde. Die Veränderung des Schichtwachstums wird anhand von Substraten mit einer definiert rauen Oberfläche im µm-Bereich sowohl experimentell als auch durch Simulationen ermittelt. Die Simulationen wurden mit dem Monte-Carlo Code SDTrimSP-2D durchgeführt, der eine detaillierte Bestimmung der lokalen zum Schichtwachstum beitragenden Mechanismen analysiert. Durch die energiereichen Ionen wird zusätzlich die molekulare Zusammensetzung der Schichten beeinflusst. Diese ist für die Materialeigenschaften wie die Haftung, Härte oder das Diffusionsverhalten bedeutend. Die molekulare Zusammensetzung der abgeschiedenen Schichten wird mittels Fourier-Transformations-Infrarot-Spektren bestimmt. Aus der Schichtzusammensetzung und dem Brechungsindex lassen sich Rückschlüsse auf das Diffusionsverhalten der abgeschiedenen Schichten bilden. Bei der Abscheidung mit Substratbias ergaben sich für das Siliziumoxid härtere Schichten, so dass diese im Vergleich zu ungebiasten Siliziumoxidschichten diffusionshemmender sind. Demgegenüber verhalten sich die Siliziumnitridschichten entgegengesetzt: Diese werden mit angelegtem Substratbias poröser und somit diffusionsfördernd.