付記する学位プログラム名: 京都大学卓越大学院プログラム「先端光・電子デバイス創成学」 / 京都大学 / 新制・課程博士 / 博士(工学) / 甲第24624号 / 工博第5130号 / 新制||工||1980(附属図書館) / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 川上 養一, 教授 野田 進, 教授 木本 恒暢 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Design, fabrication and characterization of III-Nitride pn junction devices Jae Boum Limb 94 pages Directed by Dr. Russell D. Dupuis This dissertation describes an investigation of three types of III-nitride (AlInGaN) based p-n junction devices that were grown by metalorganic chemical vapor deposition (MOCVD). The three types of devices are Ultra-Violet (UV) avalanche photodiodes (APDs), green light emitting diodes (LEDs), and p-i-n rectifiers. For avalanche photodiodes, a material growth on low-dislocation density GaN substrates, processed with low-damage etching receipes and high quality dielectric passivations, were proposed. Using this technology, GaN APDs with optical gains greater than 3000, and AlGaN APDs showing true avalanche gains have been demonstrated. For green LEDs, the use of InGaN:Mg as the p-layer, rather than employing the conventional GaN:Mg has been proposed. Green LEDs with p-InGaN have shown higher emission intensities and lower diode series resistances compared to LEDs with p-GaN. Using p-InGaN layers, LEDs emitting at green and longer wavelengths have been realized. For p-i-n rectifiers, design, fabrication and characterization of device structures using the conventional mesa-etch configuration, as well as the full-vertical method have been proposed. High breakdown devices with low on-resistances have been achieved. Specific details on device structures, fabrication methods, and characterization results are discussed.

The quality of GaN template layer plays a very important role in high electron mobility transistors. We proposed a special method in the growth of molecular beam epitaxy to deal with the dilemma between structure and the morphology of GaN. In our study, we used a nitrogen-rich GaN growth condition to deposit the initial varied layer. After that, we changed the N/Ga ratio stepwise to the growth condition of gallium-rich GaN and grew the epitaxy layer right away. In X-ray diffraction analysis, the full width at half-maximum (FWHM) value of rocking curves of GaN(002) was improved relatively to gallium-rich sample from 531.69 arcsecond to 59.43 arcsecond. In atomic force microscopy (AFM) analysis, the root mean square (rms) roughness of sample surface was improved relatively to nitrogen-rich sample from 18.28 nm to 1.62 nm over 5 £gm ¡Ñ 5 £gm area. The Raman scattering shows there is a slightly tilted plane in gradient layer and the gradient layer can also slash the strain force which is caused from Ga-rich GaN epitaxy layer and AlN buffer layer. A series high mobility AlxGa1-xN/GaN heterostructures samples were grown on MOVPE-grown GaN templates substrate by molecular beam epitaxy with different Al concentrations (x = 0.017~0.355). The quality checked by XRD and AFM indicated that the excellent properties agreed with the GaN-template. The highest mobility in this series samples at 8 K is 19593 cm2/Vs with carrier concentration 3.13 ¡Ñ 1012 cm-2 and Al concentration x = 0.017. In our experiments, the carrier density decreases as Al concentration reduces. In the illuminated Hall measurement, there are only few electrons increased following blue LED illumination. It shows that there are only few deep level defects existing near the heterointerface. From temperature-depended Shubnikov-de Haas (SdH) oscillations, the electron effective mass m* in 2DEG are evaluated as 0.213 mo and for x = 0.207 0.227 moand 0.136 respectively. The high mobility AlxGa1-xN/GaN was fabricated to a series of wires by focused ion beam (FIB) equipment, and the width of the active channel is ranged from 900 nm to 50 nm (900 nm, 500 nm, 300 nm, 200 nm, 100 nm, 80 nm and 50 nm) with the channel orientation in [11 0] direction. The largest spin-splitting energy in the series of wires is 2.14 meV. Due to larger spin-splitting energy and quasi-ballistic transportation, the 200 nm wire is the best candidate to be the channel of the quantum-ring interferometer in our case.

The spectral range of quaternary AlGaInN/AlGaN MQWs extends from UV to IR. Nitride-based green and blue LEDs reveal a high efficiency for the further application. Integrating LEDs of three element colors can perform white light. The optical properties of GaN MQWs are very sensitive to the growth conditions of MQWs. The ununiformity is not fabrication desired but needs to prevent, which is necessary to understand and to precisely control through its growth condition for manufacture the LED. In this work the sample has a luminescence varied from orange to purple across the whole wafer. In this work, the correlations between optical and structural properties in these samples have been studied by means of Transmission Electron Microscopy (TEM), energy dispersive X-ray spectrometry (EDS), and cathodoluminescence (CL) measurements.

We mainly studied the characterization of GaN/AlGaN heterostructures which were grown by molecular beam epitaxy. For reduced lattice mismatch, we inserted AlN as buffer layer. We varied the parameters of buffer layer, such as the ratio of nitrogen and aluminum and the thickness. By the analysis of X-ray diffraction, we could determine the state of mismatch. For the thickness of buffer layer, lattice mismatch is most serious at 20 minute growth. Under the observation of field emission scan electron microscopy and reflection high energy electron diffraction, we found N/Al=40 is N-face and N/Al=26 is Ga-face. For the thickness of buffer layer, the samples of 1-minute and 5-minute growth had the optimal Ga-face. For the investigation of photoluminescence, we could obtain the energy gap of AlGaN is 3.42ev. Furthermore, the doping silicon was used to vary carrier concentration, and we could show that a good Hall mobility was achieved at the doping temperature 1250¢J. We also could show good Hall mobility at 1 minute growth and 5 minute growth (N/Al=26). We tried to find the best parameters for the growth of GaN/AlGaN heterostructures.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20383号 / 工博第4320号 / 新制||工||1669(附属図書館) / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 川上 養一, 教授 藤田 静雄, 教授 木本 恒暢 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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Cette thèse s'inscrit dans le cadre du développement de transistors de puissance HEMT à base de nitrure de gallium au CEA. Les HEMT AlGaN/GaN sont des composants très prometteurs pour les applications d'électronique de puissance. Le but de cette thèse est d'étudier en détail le matériau AlGaN/GaN en amont de la fabrication de transistors. Cette thèse est organisée en quatre chapitres. Le premier chapitre introduit les concepts théoriques nécessaires à la compréhension du fonctionnement des HEMT AlGaN/GaN. Les trois chapitres restant sont consacrés à l'étude des propriétés électriques de l'empilement AlGaN/GaN: résistance de couche, résistance des contacts, mobilité et densité de porteurs. Dans le chapitre deux, à travers des mesures de la résistance de couche, il est démontré que des phénomènes de piégeage interviennent dans le matériau et que l'utilisation d'une source lumineuse permet une stabilisation de la mesure. Ensuite, à travers des structures avec des longueurs de contacts différentes, une étude détaillée des résistances de contact a été effectuée. Pour cela, le modèle TLM a été utilisé. Les résultats obtenus montre que dû à la variation non linéaire des caractéristiques de nos contacts en fonction de leur longueur, un tel modèle n'est pas adapté à l'étude des contacts fabriqués au CEA. Dans le chapitre trois, une méthode de mesure de la résistance de couche d'un empilement AlGaN/GaN sans fabrication de contacts a été mise au point. Cette méthode repose sur les travaux de Van Der Pauw concernant la mesure colinéaire et permet la caractérisation précise et rapide de plaques entières en sortie d'épitaxie. Enfin dans le dernier chapitre, une étude comparative des propriétés électriques de l'empilement AlGaN/GaN sous la grille et en dehors de la grille a été effectuée. Premièrement, on a procédé à une étude statistique de la résistance de couche, de la mobilité et de la densité de porteurs. Il est démontré que la gravure du Si3N4 préalable au dépôt de la grille injecte des ions fluor dans l'empilement, causant des dégradations des propriétés électriques. Ensuite, les phénomènes de diffusion de la mobilité ont été caractérisés à travers une étude détaillée de la mobilité en fonction de la densité de porteurs. Enfin, pour compléter cette étude, une analyse en température des mesures de capacité et de la mobilité a été effectuée. / This PhD is part of the development of HEMT power transistor based on galliumnitride at the CEA. Due to their high electron mobility, high breakdown _eld and goodthermal conductivity, AlGaN/GaN HEMT are very promising devices for power electronic applications.The goal of this PhD is, using electrical characterization, to increase the knowledge ofthe AlGaN/GaN material prior to the fabrication of transistors. First, through measurements ofthe resistance of the electron gas located at the AlGaN/GaN interface, a trapping phenomenonwas evidenced in the material. Then, in order to set a production follow-through of AlGaN/GaNon Si wafers , a method of measuring the sheet resistance of a AlGaN/GaN stack without thefabrication of contacts was developed and patented. Finally, on HEMT transistors fabricatedusing di_erent epitaxies, a detailed study of the sheet resistance, the mobility and the sheetcarrier density in and out of the gated area was carried out.

Certains domaines d'applications tels que l'aérospatial, l'automobile ou le forage de haute profondeur peuvent nécessiter la visualisation de certains paramètres physiques dans des environnements hostiles. Les capteurs microélectroniques basés sur le silicium y atteignent souvent leurs limites, qui sont qualifiées de conditions « sévères ». Ce travail se base principalement sur l'étude de solutions de capteurs mécaniques fonctionnant en conditions sévères. Le principe de ces capteurs repose sur l'exploitation de transistors de mesures HEMT à base de nitrures III-V (III-N), à la fois piézoélectriques et semiconducteurs, qui reste stable en conditions sévères. La compréhension des interactions entre physique des semiconducteurs et physique des matériaux ainsi que la caractérisation de structures possibles pour la détection mécanique représentent les principaux enjeux de ce sujet de thèse. La modélisation mécanique analytique et numérique des structures étudiées a permis d'appréhender le comportement de structures piézoélectriques multicouches. Le couplage de ce modèle électromécanique avec un modèle électronique du capteur a permis d'établir la faisabilité du principe de détection ainsi que la linéarité de la réponse du capteur. La caractérisation des prototypes réalisés en cours de thèse ont corroboré la linéarité du capteur tout en faisant apparaître l'influence de nombreux effets parasites réduisant sa sensibilité à savoir les effets de résistance parasites et de piézorésistances variables. / Some industrial areas as oil, automotive and aerospace industries, require electromechanical systems working in harsh environments. An elegant solution is to use III–V materials alloys having semiconductor, piezoelectric and pyroelectric properties. These materials, particularly nitrides such as GaN or AlN, enable design of advanced devices suitable for harsh environment. By using free-standing structure coupled with sensing HEMT transistors that are stable at high temperatures, it is possible to obtain mechanical sensors suitable for harsh environments. This PhD thesis focuses on a cantilever-based strain sensor and a drumskin-based pressure sensor. Analytical models of both sensors have been developed and establish the feasibility of the sensing principle as well as its response linearity. The characterization tests of fabricated prototypes validate the possibility of measuring external mechanical load with both sensors. The linearity of the response has also been confirmed by experimental measurements. The experimental sensitivity is smaller than the theoretical one due to several parasitic effects not included in the model such as parasitic resistance and variable piezoresisitive effects.