Polarity Control in Group-III Nitrides beyond Pragmatism

Controlling the polarity of polar semiconductors on nonpolar substrates offers a wealth of device concepts in the form of heteropolar junctions. A key to realize such structures is an appropriate buffer-layer design that, in the past, has been developed by empiricism. GaN or ZnO on sapphire are prominent examples for that. Understanding the basic processes that mediate polarity, however, is still an unsolved problem. In this work, we study the structure of buffer layers for group-III nitrides on sapphire by transmission electron microscopy as an example. We show that it is the conversion of the sapphire surface into a rhombohedral aluminum-oxynitride layer that converts the initial N-polar surface to Al polarity. With the various AlxOyNz phases of the pseudobinary Al2O3-AlN system and their tolerance against intrinsic defects, typical for oxides, a smooth transition between the octahedrally coordinated Al in the sapphire and the tetrahedrally coordinated Al in AlN becomes feasible. Based on these results, we discuss the consequences for achieving either polarity and shed light on widely applied concepts in the field of group-III nitrides like nitridation and low-temperature buffer layers

INTERACTIONS NON LINEARES EFFICACES DANS DES MICROGUIDES DE NITRURE D'ELEMENT III

En combinant EJM et EPVOM nous avons réalisés des guides d'onde à base d'AlN et de GaN mono-cristallins qui présentent de très faibles pertes à la propagation et des possibilités d'accord de phase modal intéressantes. A partir de ces structures, nous avons réalisés des guides canaux dont nous présentons les performances linéaires et non linéaires. MOTS-CLEFS : GaN, optique intégrée, optique non linéaire, pertes à la propagatio

Epitaxie localisée de P-GaN par EJM pour la fabrication de HEMTs AlGaN/GaN normally-off

National audienceThe technology of GaN HEMT structures is the subject of major developments for large-gap power components. However, it is necessary to develop innovative technological solutions to obtain high-performance normally-off devices. We present a new normally-off structure based on a nanostructured P-GaN multi-well gate. The design of this structure, based on numerical simulations, and the technological advances for its manufacture by localised epitaxy of P-GaN wells along the grid will be presented.RESUME-La technologie des structures HEMT GaN fait l'objet d'importants développements pour les composants de puissance grand gap. Cependant, il est nécessaire de développer des solutions technologiques innovantes pour obtenir des composants normally-off performants. Nous présentons une nouvelle structure normally-off basée sur une grille nanostructurée à multi-puits P-GaN. La conception de cette structure issue de simulations numériques ainsi que les avancées technologiques pour sa fabrication par épitaxie localisée des caissons P-GaN le long de la grille seront exposées

Epitaxie localisée de P-GaN par EJM pour la fabrication de HEMTs AlGaN/GaN normally-off

National audienceThe technology of GaN HEMT structures is the subject of major developments for large-gap power components. However, it is necessary to develop innovative technological solutions to obtain high-performance normally-off devices. We present a new normally-off structure based on a nanostructured P-GaN multi-well gate. The design of this structure, based on numerical simulations, and the technological advances for its manufacture by localised epitaxy of P-GaN wells along the grid will be presented.RESUME-La technologie des structures HEMT GaN fait l'objet d'importants développements pour les composants de puissance grand gap. Cependant, il est nécessaire de développer des solutions technologiques innovantes pour obtenir des composants normally-off performants. Nous présentons une nouvelle structure normally-off basée sur une grille nanostructurée à multi-puits P-GaN. La conception de cette structure issue de simulations numériques ainsi que les avancées technologiques pour sa fabrication par épitaxie localisée des caissons P-GaN le long de la grille seront exposées

Crystalline Quality and Surface Morphology Improvement of Face-to-Face Annealed MBE-Grown AlN on h-BN

In this study, AlN epilayers were grown by ammonia-assisted molecular beam epitaxy on 3 nm h-BN grown on c-sapphire substrates. Their structural properties were investigated by comparing as-grown and postgrowth annealed layers. The role of annealing on the crystalline quality and surface morphology was studied as a function of AlN thickness and the annealing duration and temperature. Optimum annealing conditions were identified. The results of X-ray diffraction showed that optimization of the annealing recipe led to a significant reduction in the symmetric (0 0 0 2) and skew symmetric (1 0 −1 1) reflections, which was associated with a reduction in edge and mixed threading dislocation densities (TDDs). Furthermore, the impact on the crystalline structure of AlN and its surface was studied, and the results showed a transition from a surface with high roughness to a smoother surface morphology with a significant reduction in roughness. In addition, the annealing duration was increased at 1650 °C to further understand the impact on both AlN and h-BN, and the results showed a diffusion interplay between AlN and h-BN. Finally, an AlN layer was regrown on the top of an annealed template, which led to large terraces with atomic steps and low roughness

CVD Elaboration of 3C-SiC on AlN/Si Heterostructures: Structural Trends and Evolution during Growth

(111)-oriented cubic polytypes of silicon carbide (3C-SiC) films were grown by chemical vapor deposition on 2H-AlN(0001)/Si(111) and 2H-AlN(0001)/Si(110) templates. The structural and electrical properties of the films were investigated. For film thicknesses below 300 nm, the 3C-SiC material deposited on 2H-AlN/Si presented a better structural quality than the 3C-SiC films grown directly on Si(111) using the well-established two-step carbonization–epitaxy process. The good lattice match of 3C-SiC with AlN may open a reliable route towards high-quality thin heteroepitaxial 3C-SiC films on a silicon wafer. Nevertheless, the 3C-SiC was featured by the presence of twinned domains and small inclusions of 6H-SiC. The formation of a thin AlSiN film at the AlN/Si interface is also reported. This is the first time such AlSiN layers are described within an AlN/Si heterostructure. Furthermore, noticeable modifications were observed in the AlN film. First, the growth process of SiC on AlN induced a reduction of the dislocation density in the AlN, attesting to the structural healing of AlN with thermal treatment, as already observed for other AlN-based heterostructures with higher-temperature processes. The growth of SiC on AlN also induced a dramatic reduction in the insulating character of the AlN, which could be related to a noticeable cross-doping between the materials

Origine du twist entre les îlots de croissance de semi-conducteurs tétra-coordonnés hétéroépitaxiés selon des directions hexagonales.

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Origine du twist entre les îlots de croissance de semi-conducteurs tétra-coordonnés hétéroépitaxiés selon des directions hexagonales.

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On the origin of twist in 3D nucleation islands of tetrahedrally coordinated semiconductors heteroepitaxially grown along hexagonal orientations

International audienceIn the first part of this paper, we present a model that explains and determines quantitatively the twists between nucleation islands in the case of a Volmer–Weber heteroepitaxial growth of tetrahedrally coordinated semiconductors along hexagonal orientations. These twists are caused by the network of the screw components of the 60° misfit dislocations. The orientations of the screw components are distributed randomly, and the maximum twist is obtained when all the screw components have the same orientation. The maximum twists are related to the density of misfit dislocations and, therefore, increase with the mismatch between the deposited materials and their substrate. In the second part of the paper, we study five systems having a large distribution of mismatches from 4% to 19%. For the four systems fulfilling the conditions necessary for the application of the model (plastic relaxation of grown islands), the measured maximum twists fit with the calculated values, thereby validating the model. The twists of nucleation islands are related to the mismatch and are, therefore, intrinsic to the material systems. The defects created at the coalescence of twisted islands determine the initial microstructure/defect distribution of the nucleation layer

Efficient second harmonic generation in low-loss planar GaN waveguides

International audienc