Characterization and physical modelling of contacts between metallic phases and Gallium Nitride

Les composés III-N, et le Nitrure de Gallium (GaN) en particulier, sont devenus des matériaux semi conducteurs importants pour l’ensemble de l’humanité. Depuis la fin des années 1990, ils ont permis le développement de composants électroluminescents fiables, diodes LED et diodes laser, qui constituent une solution de remplacement à rendement énergétique amélioré par rapport aux composants à incandescence. Il est possible qu’ils jouent aussi un rôle dans les nouvelles générations de composants pour l’électronique de puissance. Lors du développement des composants, des recherches expérimentales permettent de trouver assez rapidement des solutions pour réaliser les briques technologiques indispensables, mais le temps manque pour comprendre les mécanismes physiques mis en jeu. Nos travaux ont eu pour objectif d’approfondir la compréhension de l’influence de la structure physico-chimique sur les propriétés électriques des contacts ohmiques et Schottky sur GaN de type N.Group III nitride semiconductor materials (III-N), and especially gallium nitride (GaN), are now key materials for the whole human kind. Since years 1990, reliable and energy-efficient light emitting devices have been developed based on III-N compounds providing higher efficiency replacement solutions to incandescent bulbs. The same III-N materials may also provide higher performance device solutions for power electronics, allowing multi-functional on-chip integration. During the industrial development of devices, experimental work is focused on finding rapidly good enough solutions for each technology brick, and on the eventual integration of the bricks into a complete device processing flow. Very often, little time and effort can be devoted to the understanding of the underlying physical and chemical processes. The aim of this work has been to study the influence of the physical and chemical material structures on the electrical properties of metal - GaN Ohmic and Schottky contacts

Caractérisations et modélisations physiques de contacts entre phases métalliques et Nitrure de Gallium semi-conducteur

Group III nitride semiconductor materials (III-N), and especially gallium nitride (GaN), are now key materials for the whole human kind. Since years 1990, reliable and energy-efficient light emitting devices have been developed based on III-N compounds providing higher efficiency replacement solutions to incandescent bulbs. The same III-N materials may also provide higher performance device solutions for power electronics, allowing multi-functional on-chip integration. During the industrial development of devices, experimental work is focused on finding rapidly good enough solutions for each technology brick, and on the eventual integration of the bricks into a complete device processing flow. Very often, little time and effort can be devoted to the understanding of the underlying physical and chemical processes. The aim of this work has been to study the influence of the physical and chemical material structures on the electrical properties of metal - GaN Ohmic and Schottky contacts.Les composés III-N, et le Nitrure de Gallium (GaN) en particulier, sont devenus des matériaux semi conducteurs importants pour l’ensemble de l’humanité. Depuis la fin des années 1990, ils ont permis le développement de composants électroluminescents fiables, diodes LED et diodes laser, qui constituent une solution de remplacement à rendement énergétique amélioré par rapport aux composants à incandescence. Il est possible qu’ils jouent aussi un rôle dans les nouvelles générations de composants pour l’électronique de puissance. Lors du développement des composants, des recherches expérimentales permettent de trouver assez rapidement des solutions pour réaliser les briques technologiques indispensables, mais le temps manque pour comprendre les mécanismes physiques mis en jeu. Nos travaux ont eu pour objectif d’approfondir la compréhension de l’influence de la structure physico-chimique sur les propriétés électriques des contacts ohmiques et Schottky sur GaN de type N

Characterization and kinetic monitoring of the reactions between TixAly phases in Ti-Al based ohmic contacts on n-type GaN by Differential Scanning Calorimetry (DSC)

International audienceThis work reports on DSC measurements performed on Ti-Al metallic layers stacks deposited on n+-GaN. The aim is to get better understanding of the mechanisms leading to ohmic contact formation during the annealing stage. Two exothermic DSC peaks were found : one below 500°C and the other one around 660°C. They can be respectively attributed to Al3Ti and Al2Ti compounds formation. Lowest contact resistance is well correlated with the presence of Al3Ti compound, corresponding to Al(200nm) / Ti(50nm) stoichiometric ratio. Subsequently, Al (200 nm) / Ti(50 nm) stacks on n+-GaN were comparatively annealed from 400 °C to 650 °C. Specific Contact Resistivity (SCR) values stay in the mid 10-5 Ω.cm 2 range for annealing temperatures between 450 °C and 650 °C. Such low-temperature annealed contacts on n+-GaN may open new device processing routes, simpler and cheaper, in which Ohmic and Schottky contacts are annealed together

Evidence of Low Temperature Decomposition of GaN Hetero-Epitaxial Layers on C-Plane Sapphire Surface Characterized by Differential Scanning Calorimetry

International audienceThis work reports on the characterization of the decomposition of GaN layers epitaxied on c-plane Sapphire substrate by Differential Scanning Calorimetry. Many configurations have been characterized from two different GaN epilayer providers with a large range of doping concentrations from Non-intentionally Doped layers up to 2x1019 cm-3. All intentionally doped layers exhibit an endothermic reaction starting at 200-300 °C while the NiD layer thermogram is the same as the blank experiment. XPS and SEM observations demonstrated that the endothermic reaction is related to the GaN decomposition through Threading Dislocation and nanoPipe

Active Devices for Power Electronics: SiC vs III-N Compounds – The Case of Schottky Rectifiers

International audienceThe main rectifier device structures for power electronics based on SiC and on GaN are compared and the main issues for each structure are evaluated in terms of performance and manufacturability. The driving volume markets for power electronics devices correspond to the systems working on 127, 240 and 400 V energy supply networks, setting the device voltage handling to 300, 600, and 1200V respectively. We have limited the scope hereafter to the 600 V typical target, for which SiC Schottky rectifiers are now commercially available from at least 3 sources. The key physical properties for any semiconductor material used as the active layer of a unipolar device for power electronics are the breakdown field and carriers mobility. The bulk values are very similar for SiC and GaN. Two main other key issues are related to quality of the ohmic and Schottky contacts. For the ohmic contacts, adequate solutions have been found for both SiC and GaN. Surprisingly, on hetero-epitaxial GaN layers on sapphire despite of the very high crystal defects density ( ≥ 109cm-2 ), the ideality factor of the best Schottky contacts seems very promising. On the other hand, improving this ideality factor and the reverse leakage current for Schottky contacts on GaN layers grown on silicon substrate remains a fierce challenge. For the SiC Schottky rectifiers, cost and availability of the SiC substrates appear as the main residual limiting factors today. For GaN based rectifiers, although engineering device prototypes have already been published [1], there are both basic issues to be validated regarding reverse leakage current and reliability, and also difficult manufacturing issues to be solved in relation with device reliability, directly resulting from the nature of the possible substrates: mainly sapphire and silicon

SiC Power Devices Operation from Cryogenic to High Temperature: Investigation of Various 1.2kV SiC Power Devices

International audienceThe aim of this study consists in comparing the effects of temperature on various SiC power devices. Electrical characteristics have been measured for temperatures from 100K to 525K. All devices are suitable for high temperature. However, SiC MOSFETs are not a good choice for cryogenic temperature, while SiC BJTs are less affected by temperature than other components, especially for cryogenic temperature

Observation of the generation of stacking faults and active degradation measurements on off-axis and on-axis 4H-SiC PiN diodes

International audiencePiN diodes have been fabricated on nominally on-axis Si-face 4H-SiC material and their electrical characteristics are compared to PiN diodes processed with exactly the same device process recipe on 8°-off 4H-SiC material. Some diodes had an optical window on the top metal contact to observe the possible stacking faults generation and motion with photo emission microscopy. The diodes were electrically characterized in forward voltage to test their stability. Electrical characterizations demonstrate that there is no noticeable degradation for the diodes processed on on-axis 4H-SiC substrate and with optical characterization the formation of stacking faults was not observed

Study and Optimization of a 600V Pseudo-Vertical GaN-on-Silicon Rectifier by Finite Element Simulations

International audienceThis work presents the impact analysis of physical and geometrical parameters on the on-resistance and the breakdown voltage in order to optimize a 600 V pseudo-vertical GaN/Si Schottky rectifier. The results by finite element simulations indicate that the most influent parameter on the resistance is the thickness of the n+ layer. Regarding reverse specifications, simulations show that a good efficiency of the “Mesa + Guard Ring” is achieved for a guard ring doping concentration higher than Na=5×1017 cm-3