Interplay of bonding and electronic properties at diamond interfaces

International audiencePotential discontinuities and spatial profiles govern the electronic properties of elementary devices like Schottky diodes and metal/insulator/semiconductor (MOS) structures. At interfaces between oxygenated diamond and other materials, two situations are examined: (1) Zr Schottky contact; (2) MOS capacitors, mainly using Al2O3 as an insulator.In the first case, we give two experimental evidences of potential barrier inhomogeneities and/or domains, which almost vanish after annealing at 450°C, with a simultaneous decrease of the homogeneous barrier height of 1.4 eV, analogous to the change in electronic affinity when the oxygen terminations disappear from the surface. This evolution is the same for 4 other metals. The model able to comply with these experimental facts relies on the Mott-Schottky linear relationship which links the barrier height and the electronic affinity at a zero order of approximation, and on a correction term proportional to the charge transfer in interface bonds. This last term is able to justify the reverted slope observed regarding the dependence of the barrier height on the metal work function.In the second case, a capacitance measurement method is developed in order to show the projected interface states density and Fermi level pinning at the Al2O3 /oxygenated diamond interface of MOS capacitors. Reasons for these results, based on bonding between carbon, adsorbates and insulator atoms, and possible routes to free the interface from this Fermi level pinning are discussed

La diode Schottky en diamant : le présent et le futur

International audienceDes diodes Schottky en diamant avec une structure pseudo-verticales montrant une densité de courant de 10^3A/cm2 (à 6V) avec un champ de claquage supérieur à 7.7MV/cm ont été réalisées. Ces diodes ont été obtenues par croissance homoépitaxiale du diamant avec le zirconium comme métal de contact Schottky. Ces résultats ont permis d'avoir le record mondial actuel du facteur de Baliga pour le diamant avec 244MV/cm^2. Ces travaux montrent que les potentialités du diamant ne sont pas uniquement théoriques. La maitrise actuelle des interfaces et de la croissance permettent d'imaginer des composants de puissance performant en poussant le diamant dans ses retranchements

Hole injection contribution to transport mechanisms in metal/p− /p++and metal/oxide/p− /p++ diamond structures

International audienceHeterostructures such as Schottky diodes and metal/oxide/semiconductor structures are the building blocks of diamond electronic devices. They are able to carry large current densities, up to several kA/cm$^2$, if a heavily boron doped layer (p$^{++}$) is included in the semiconducting stack, thus affording a metallic reservoir of mobile holes close to the lightly doped layer (p$^{-}$). In this work, hole injection effects are evidenced experimentally in the two previously mentioned devices and also simulated numerically. Although the potential barrier height at metal/semiconductor interfaces is a fundamental parameter, a more general approach consists in defining the current density from the product of an effective velocity and carrier concentration at interface. In accordance with experimental results, such a view permits to describe both depletion and accumulation regimes, which indeed can exist at the metallic or oxide interface, and to take into account the increase of the hole concentration above the thermal equilibrium one in the p$^{-}$ layer. The lower the temperature, the larger is this second effect. For sufficiently thin p$^{-}$ layers, typically below 2~$\mu$m, this effect frees device operation from the limitation due to incomplete ionization of acceptors and allows a strong decrease of the specific resistance and forward losses while preserving breakdown voltages in the range 1.4 to 2 kV

Zr/oxidized diamond interface for high power Schottky diodes

International audienceHigh forward current density of 103 A/cm2 (at 6 V) and a breakdown field larger than 7.7 MV/cm for diamond diodes with a pseudo-vertical architecture, are demonstrated. The power figure of merit is above 244 MW/cm2 and the relative standard deviation of the reverse current density over 83 diodes is 10% with a mean value of 10 9 A/cm2. These results are obtained with zirconium as Schottky contacts on the oxygenated (100) oriented surface of a stack comprising an optimized lightly boron doped diamond layer on a heavily boron doped one, epitaxially grown on a Ib substrate. The origin of such performances are discussed

Recent progress of diamond device toward power application

International audienceThe state of the art of the Institut Néel research activity in the field of diamond power devices will be described and discussed. The active layers of the device are based on boron-doped monocristalline (100) diamond (with doping level varying between 1014 to 1021 cm-3) grown on Ib high temperature high pressure (HPHT) diamond substrate. The progresses done on diamond/metal interface, diamond/dielectric interface, or sharp gradient doping, permit recently the fabrication of original structures and devices, which will be detailed here (Schottky diode, boron doped δ-FET and MOS capacitance)

Tropical Data: Approach and Methodology as Applied to Trachoma Prevalence Surveys

PURPOSE: Population-based prevalence surveys are essential for decision-making on interventions to achieve trachoma elimination as a public health problem. This paper outlines the methodologies of Tropical Data, which supports work to undertake those surveys. METHODS: Tropical Data is a consortium of partners that supports health ministries worldwide to conduct globally standardised prevalence surveys that conform to World Health Organization recommendations. Founding principles are health ministry ownership, partnership and collaboration, and quality assurance and quality control at every step of the survey process. Support covers survey planning, survey design, training, electronic data collection and fieldwork, and data management, analysis and dissemination. Methods are adapted to meet local context and needs. Customisations, operational research and integration of other diseases into routine trachoma surveys have also been supported. RESULTS: Between 29th February 2016 and 24th April 2023, 3373 trachoma surveys across 50 countries have been supported, resulting in 10,818,502 people being examined for trachoma. CONCLUSION: This health ministry-led, standardised approach, with support from the start to the end of the survey process, has helped all trachoma elimination stakeholders to know where interventions are needed, where interventions can be stopped, and when elimination as a public health problem has been achieved. Flexibility to meet specific country contexts, adaptation to changes in global guidance and adjustments in response to user feedback have facilitated innovation in evidence-based methodologies, and supported health ministries to strive for global disease control targets

Diode Schottky haute puissance sur substrat diamant

This thesis was focused on high power diamond Schottky diodes fabrication. Diamond growth and its doping are today well mastered. The advent of vertical architectures (diode active layer grown on heavily doped diamond substrate) and pseudo-vertical (stack of diode active layer and heavily doped layer grown on insulating substrate) allowed minimizing the high serial resistance, which was induced by the high ionization energy of acceptor-type dopants (boron doped diamond) preferably used in rectifiers fabrications.Besides these geometrical configurations favoring high forward currents, diamond Schottky diodes (pseudo vertical or vertical structures) were limited by: I) the quality of diode active layer altered by defects propagation from heavily doped layer thus leading to lower blocking voltage (maximum critical field of 3 MV/cm reported) than the theoretical values (theoretical values of critical field of 10 MV/cm), II) Schottky electrodes selected and the thermal and chemical stability of interfaces formed with oxygen-terminated diamond surface (required getting a Schottky contact and reducing as much as possible the interface states). Schottky metal selection and diamond surface pretreatment are crucial to get low barrier heights (low forward voltage drop and so low losses), low defects density at interfaces (low leakage current), and a thermally stable interface (high operating temperature). In this thesis, we demonstrated that a pseudo vertical diamond Schottky diode based on an oxygen-terminated surface covered by an easily oxidizable metal like zirconium (Zr) combined with an optimal heavily doped layer, allows overcoming these limitations. We first found a trade-off between the thickness of heavily doped layer and its doping level in order to minimize defects generations and thus improve the quality of diode active layer grown on the heavily doped layer (Less defects propagations). On a second hand, the Zr metallic electrodes selected gave rise to a thin zirconia interface layer which was thermally stable thus preventing the oxygen layer desorption. Zr/oxidized diamond rectifiers exhibited better features than the current state of art: a high forward current density (1000 A/cm2 at 6 V), a high critical field above 7 MV/cm (1000 V blocking voltage with a leakage current less than 1 pA), a Baliga's power figure of merit above 244 MW/cm2 (the highest value reported), a good reproducibility regardless of diodes and samples, the possibility to get a barrier heights below 1 eV by annealing, and a thermal stability higher than 500°C.Cette thèse porte sur la fabrication de diodes Schottky sur diamant pour des applications hautes puissances. La croissance du diamant et son dopage sont aujourd'hui bien maîtrisés. La passivation de la surface du diamant (surface à terminaison oxygène) requise pour minimiser les états d'interface et obtenir des contacts redresseurs sur diamant, est également bien maîtrisé. L'apparition des architectures verticales (couche active des diodes épitaxiée sur un substrat de diamant fortement dopée) et pseudo-vertical (épitaxie d'un empilement comprenant la couche active et une couche fortement dopée sur un substrat diamant isolant) ont permis de minimiser la résistance série élevée des diodes sur diamant (énergie d'ionisation élevée des principaux dopants du diamant). Malgré le fait que ces configurations géométriques favorisent courants directs élevés, les performances diodes Schottky verticales ou pseudo verticales sur diamant sont à ce jour limitées par: i) la qualité de la couche active altérée par la propagation de défauts issues de la couche fortement dopée conduisant à de faible champ critiques (environ 3 MV / cm au lieu des 10MV/cm théorique), ii) les contacts Schottky sélectionnés, la stabilité thermique et chimique des interfaces formées avec une surface de diamant à terminaison oxygène. La sélection du métal Schottky et le prétraitement de la surface sont cruciaux pour obtenir de faibles hauteurs barrières (faible chute de tension à l'état passant), une faible densité de défauts au niveau des interfaces (faible courants de fuite), et une interface thermiquement stable (température de fonctionnement élevée). Dans cette thèse, nous avons démontré qu'une diode Schottky diamant pseudo verticale basée sur l'utilisation d'une surface à terminaison oxygène couverte par un métal facilement oxydable comme le zirconium (Zr), et une couche fortement dopée avec une épaisseur optimale, permettent de surmonter ces limitations et de fabriquer des diodes de meilleurs performances que l'état de l'art actuel. Un compromis entre l'épaisseur de la couche fortement dopée et son niveau de dopage à été d'abord établit afin de minimiser la génération de défauts et par conséquent d'améliorer la qualité de la couche active. Le métal (Zr) sélectionné comme contact Schottky donnait lieu à la formation d'une fine couche d'oxyde de zirconium thermiquement stable entre le Zr et le diamant. Les redresseurs fabriqués avaient: une forte densité de courant direct (1000 A par centimètre carré à 6 V), un champ critique supérieur à 7.7 MV /cm (tension de blocage 1000 V avec un courant de fuite inférieur à 1 pA), un facteur de mérite de Baliga supérieur à 244 MW par centimètre carré (la valeur la plus élevée signalée), une bonne reproductibilité indépendamment de la taille des diodes et des échantillons, la possibilité d'obtenir une hauteur de barrière inférieure à 1 eV après recuit, et une stabilité thermique supérieure à 500 ° C

Surface defects related to polishing cycle in ß-Ga2O3 crystals grown by floating zone

International audienceWe report an investigation on ß-Ga2O3 Schottky barrier diodes performed on substrates grown by floating-zone method using structural characterization techniques (secondary-ion mass spectrometry, inductively coupled plasma-mass spectroscopy, and atomic force microscopy) and electrical measurements (current-voltage, capacitance-voltage, Hall effect, and capacitance deep-level transient spectroscopy). Four distinct electron trap levels labeled ES, E1, E2, and E3 were found in the range of 1 eV below the Ga2O3 conduction band minimum. Among them, E1, E2, and E3 show signatures similar to those reported in the literature for Czochralski and edge-defined film-fed grown ß-Ga2O3 substrates. Trap ES was found near the surface, and we could establish a link between this defect and the damage induced by the substrate polishing technique. The level related to ES was identified at ∼0.31 eV below the conduction band minimum. An energy band above 0.31 eV was also detected and is associated with states at the metal–semiconductor interface. We demonstrated that the interface states and surface deep traps are not uniformly distributed on the ß-Ga2O3 surface. Furthermore, they contribute to the reverse leakage current and the on-state conduction degradation of the diodes

Diamond Electronic Devices

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Delta doping for advanced diamond devices

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