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

Realization of minimum number of rotational domains in heteroepitaxied Si(110) on 3C-SiC( 001)

Structural and morphological characterization of a Si(110) film heteroepitaxied on 3C-SiC(001)/ Si(001) on-axis template by chemical vapor deposition has been performed. An antiphase domain (APD) free 3C-SiC layer was used showing a roughness limited to 1 nm. This leads to a smooth Si film with a roughness of only 3 nm for a film thickness of 400 nm. The number of rotation domains in the Si(110) epilayer was found to be two on this APD-free 3C-SiC surface. This is attributed to the in-plane azimuthal misalignment of the mirror planes between the two involved materials. We prove that fundamentally no further reduction of the number of domains can be expected for the given substrate. We suggest the necessity to use off-axis substrates to eventually favor a single domain growth

Freestanding-quality dislocation density in semipolar GaN epilayers grown on SOI: aspect ratio trapping

International audienc

Direct Insight into Grains Formation in Si Layers Grown on 3C-SiC by Chemical Vapor Deposition

International audienc

Realization of minimum number of rotational domains in heteroepitaxied Si(110) on 3C-SiC( 001)

Structural and morphological characterization of a Si(110) film heteroepitaxied on 3C-SiC(001)/ Si(001) on-axis template by chemical vapor deposition has been performed. An antiphase domain (APD) free 3C-SiC layer was used showing a roughness limited to 1 nm. This leads to a smooth Si film with a roughness of only 3 nm for a film thickness of 400 nm. The number of rotation domains in the Si(110) epilayer was found to be two on this APD-free 3C-SiC surface. This is attributed to the in-plane azimuthal misalignment of the mirror planes between the two involved materials. We prove that fundamentally no further reduction of the number of domains can be expected for the given substrate. We suggest the necessity to use off-axis substrates to eventually favor a single domain growth

Realization of minimum number of rotational domains in heteroepitaxied Si(110) on 3C-SiC( 001)

Structural and morphological characterization of a Si(110) film heteroepitaxied on 3C-SiC(001)/ Si(001) on-axis template by chemical vapor deposition has been performed. An antiphase domain (APD) free 3C-SiC layer was used showing a roughness limited to 1 nm. This leads to a smooth Si film with a roughness of only 3 nm for a film thickness of 400 nm. The number of rotation domains in the Si(110) epilayer was found to be two on this APD-free 3C-SiC surface. This is attributed to the in-plane azimuthal misalignment of the mirror planes between the two involved materials. We prove that fundamentally no further reduction of the number of domains can be expected for the given substrate. We suggest the necessity to use off-axis substrates to eventually favor a single domain growth

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

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

National audienc

High quality GaN microplatelets grown by metal-organic vapor phase epitaxy on patterned silicon-on-insulator substrates: Toward micro light-emitting diodes

In this paper, we report the use of three pendeo-epitaxy growth approaches as a way of reducing the threading dislocation density (TDD) of 20 × 20 μm2 GaN platelets to be used for the development of micro light-emitting diodes (μLEDs). The method relies on the coalescence of GaN crystallites grown on top of a network of deformable pillars etched into a silicon-on-insulator substrate. Our approach takes advantage of the creeping properties of SiO2 at the usual GaN epitaxial growth temperature, allowing the GaN crystallites to align and reduce the grain boundary dislocations. Furthermore, this bottom-up approach allows to get rid of the dry plasma etching step for μLEDs fabrication, which highly deteriorates sidewalls, reducing the efficiency of future displays. By optimizing the growth conditions and inducing asymmetric nucleation, a TDD of 2.5 × 108 cm−2 has been achieved on the GaN platelets, while keeping a smooth surface