Today, global electrification requires new materials for power applications. 4H-SiC dominates the market due to its excellent energy efficiency and wide operating range. This study explores the formation of Ni/4H-SiC backside ohmic contacts using 308 nm nanosecond laser annealing (NLA). After depositing an 80 nm layer of Ni onto 4H-SiC wafers through sputtering, different laser annealing parameters were tested. The energy densities (ED) ranged from 2.4 to 5.4 J cm-2, the number of laser pulses applied varied from 1 to 20, and the chuck temperatures from 25 to 400 degrees C. For all series, a common scenario was observed as a function of ED, with initial solid state reactions, then local melting, and finally complete melting and dewetting of the top layer at high ED. An in-depth understanding of the effect of laser conditions on these stages is proposed based on electrical data, Raman spectroscopy, optical microscopy, scanning electron microscopy and transmission electron microscopy cross analysis. Increasing the pulse number and using a heated chuck can substantially lower the energy density (ED) necessary to achieve low-resistance contacts. In addition, trends in sheet resistivity and contact resistivity are related to microstructural evolution during NLA exposure. A contact resistivity of around 5 x 10-5 Omega.cm2 is obtained when the wafer is processed at 25 degrees C. It drops to 10-5 Omega.cm2 when processed at 400 degrees C.

We demonstrate the application of atom probe tomography for assessing the crystalline orientation of nanoscale semiconductor structures via the analysis of charge state ratio maps in the detector space. The experimental realization is carried out in the context of adventitious cone-shaped domains present in AlGaN quantum dot superlattices. The cone-shaped domains, which emerge from shallow pits generated in AlN and propagate through the superlattices, are shown to exhibit small misorientation angles of their crystalline 〈0001〉 poles. The results of the atom probe tomography analysis are confirmed by convergent beam electron diffraction measurements. The use of this methodology adds another layer to the application of this technique to semiconductor nanoscale systems, providing not only compositional maps but also information on the crystallographic orientation.

Neural Network hardware in-memory implementations based on memristive synapses are a promising path towards energy efficient Edge computing. Among others, Oxide-based Resistive Random Access Memory (OxRAMs) devices utilization for synaptic weight hardware implementation has shown promising performance on various types of Neural Networks, notably when coupled with bit-error correcting codes or adaptive programming schemes for the device intrinsic variability management. In this context, memristive footprint reduction coupling with Multi-Level-Cell (MLC) operation remains essential to hardware implement highly accurate state-of-art Neural Networks, whose number of parameters is exponentially increasing over time. In this work, a compact OxRAM-based 1 Transistor – 1 Resistor (1T1R) architecture, where the memory is integrated inside the 40 nm × 40 nm drain contact of thin-gate oxide FDSOI transistors, is demonstrated in 28 nm technology. The memory structure is optimized from the OxRAM active material level to the cell architecture. This results in 106 endurance and 11-level MLC encoding resilient to 109 inference cycles compatible with 0.0357 μm2 bitcell footprint potential in 28 nm technology. Altogether, the proposed 1T1R cell density is competitive with respect to ultra-dense 1S1R-based Crossbar arrays, while being compatible with in-memory Neural Network inference implementations on-chip.

Selective area growth (SAG) of GaN nanowires was performed on GaN on c-plane sapphire templates masked with SiN using hydride vapor phase epitaxy (HVPE). GaN nanowires exhibited various morphologies, discussed as a function of the pattern design, the partial pressure of the Ga gaseous precursor, the composition of the carrier gas, and the growth temperature. The morphologies are elucidated by involving a comparative study of growth rates of facets relative to each other. CL measurements showed high emission quality for GaN nanowires grown at 930 degrees C. This work places HVPE as an effective epitaxial technique for growing III-N nanostructure-based devices at a low cost.

To fabricate native and monolithic full color micro-displays with a pixel pitch below 10 µm, the three primary colors should be achieved with the InGaN alloy. The prerequisite is to get an efficient red emission with thin InxGa1-xN quantum well (QW) width and an In content of 35%. However, the In content is limited to 25% when grown on GaN. A full InGaN structure combined with different types of relaxed InGaN pseudo-substrates are used to reduce the strain in the active zone. Red electroluminescence was obtained until 650 nm. Homogeneous red emitting InGaN based QWs were also demonstrated.

In this paper, a comparative study of C-, N- and Xe-based pre-amorphization implantation (PAI) processes is proposed. The impact of the use of such processes on the agglomeration resistance and physical properties of the final Ni( Pt )Si layer, as well as the formation mechanisms via solid-state reactions and electrical performances via the transfer length measurement (TLM) method, is evaluated. It is shown that although all species are able to increase the agglomeration temperature of Ni( Pt )Si layers (up to more than 100 degrees C), the underlying mechanisms are different. For C- and N-based PAI processes a strong chemical effect is observed, while for Xe-based processes the amorphization depth plays an important role. Consequently, the beneficial effect of stabilizing Ni( Pt )Si layers at high temperatures using C- and N-based PAI processes has to be balanced with an increased layer resistivity (up to 30%) combined with a strong deterioration of the associated specific contact resistivity (which is multiplied by almost a factor 10). In this sense, Xe-based PAI processes seem to be a better option as they could allow to combine both requirements.

AbstractFull color micro-displays with a pixel pitch of below 10 µm are needed for augmented and virtual reality applications. In the native emission approach, high efficiency Red-Green-Blue (RGB) pixels could be achieved using monolithically integrated InGaN based micro-LEDs. Here, we report the growth of high optical quality RGB InGaN/InGaN quantum wells grown on InGaN nanopyramids of diameter less than 1 µm by metal organic vapor phase epitaxy. We synthesized the nanopyramids by nanoselective area growth using an in situ patterned epitaxial graphene on SiC as an embedded mask. The RGB emission properties at different locations on the sample are dependent on the size of the InGaN nanopyramids. Advanced correlative analysis conducted on the same transmission electron microscopy lamella reveal a fully or at least nearly relaxed In0.13Ga0.87N core and very regular quantum wells emitting in the red range (620 nm) along the pyramid sidewalls with an In content up to 40%.

Nowadays, the growing worldwide electrification requires new materials for power management. SiC currently dominates the market thanks to excellent energy efficiency and broad operating capabilities. The present paper proposes an experimental study of the Ni-SiC backside ohmic contact formation using 308 nm nanosecond laser annealing (NLA). After Nickel (80 nm) sputtering over 4H-SiC wafers, various laser conditions are investigated, with energy density (ED) ranging from 2.4 to 5.4 J/cm², pulse number from 1 to 20 and chuck temperature from 25 °C (RT) to 400 °C. For all series, a common scenario is noticed as the ED increases, with first solid-state reactions, then local melt and, finally, complete top layer melt and de-wetting at high ED. An in-depth understanding of the impact of laser conditions on these stages is achieved, based on electrical data, Raman spectroscopy, optical microscopy, Scanning Electron Microscopy (SEM) and Scanning Transmission Electron Microscopy (STEM). Results reveal that both high pulse numbers and the use of a hot chuck enable to significantly reduce the ED needed to form low resistance contacts. In addition, sheet resistances and contact resistivities are linked to the microstructure evolution upon NLA exposure. As a proof-of-concept, an acceptable process point yields a contact resistivity around 5×10 -5 Ω cm² when the wafer is processed at 25 °C and a value as low as 10 -5 Ω cm² for 400 °C processing. The mechanisms involved and discussed in the present work may very likely pave the way for other contact formation with limited thermal budget.

We study the origin of bimodal emission in AlGaN/AlN QD superlattices displaying a high internal quantum efficiency (around 50%) in the 230-300 nm spectral range. The secondary emission at longer wavelengths is linked to the presence of cone-like domains with deformed QD layers, which originate at the first AlN buffer/superlattice interface and propagate vertically. The cones originate at a 30 degrees-faceted shallow pit in the AlN, which appears to be associated with a threading dislocation that produces strong shear strain. The cone-like structures present Ga enrichment at the boundaring facets and larger QDs within the conic domain. The bimodality of the luminescence is attributed to the differing dot size and composition within the cones and at the faceted boundaries, which is confirmed by the correlation of microscopy results and Schrodinger-Poisson calculations.

This study investigates the influence of substrate temperature and III/V ratio on the synthesis of Mg-doped GaN layer using plasma-assisted molecular beam epitaxy. We demonstrate that optimum growth conditions are the result of a delicate balance between substrate temperature, Mg flux, and III/V ratio. At low substrate temperatures, where Ga desorption from the growing surface is negligible, a pronounced self-compensation effect linked to polarity inversion significantly reduces net acceptor concentration at relatively low Mg cell temperatures. Increasing the substrate temperature allows for higher Mg fluxes, enhancing the net acceptor concentration before reaching the collapse due to polarity inversion. Detailed analysis of Ga desorption during growth interruptions highlights the susceptibility of the Ga bilayer to perturbations under varying Mg fluxes, attributed to the replacement of Ga adatoms by Mg. We demonstrate that the polarity inversion is triggered when the Ga bilayer is reduced to a monolayer, either by the influence of the Mg flux or by a reduction of the Ga flux. This study demonstrates that maintaining a substantial Ga excess, within the bilayer regime and close to the Ga droplet accumulation threshold, is vital for preventing polarity inversion.

Aluminum nitride (AlN) is a wide bandgap material used in acoustic devices, piezo- micro-electromechanical system and is promising for other electronic applications. However, for most applications, the AlN crystalline quality obtained by PVD or MOCVD is insufficient, and suitable growth substrates providing an adapted lattice match and coefficient of thermal expansion are limited. Alternatively, monocrystalline AlN wafers are not yet available in 200/300 mm sizes and suffer from high costs and quality issues. Here, we propose a novel approach involving a two-dimensional transition metal dichalcogenide (TMD) material as a seed layer, which displays an excellent lattice matching with AlN (>98%) allowing a strong enhancement in the c axis texture of sputtered AlN layers on Si(100)/SiO2 thermal oxide (500 nm) substrates. We have successfully demonstrated an eightfold improvement of the AlN (002) rocking curve compared to reference samples grown on thermal SiO2, thus providing a relevant and cost-effective process for the large-scale deployment of high-quality III-N materials on silicon-based substrates.

We study the origin of bimodal emission in AlGaN/AlN QD superlattices displaying high internal quantum efficiency (around 50%) in the 230-300 nm spectral range. The secondary emission at longer wavelengths is linked to the presence of cone-like defects starting at the first AlN buffer/superlattice interface and propagating vertically. These defects are associated with a dislocation that produces strong shear strain, which favors the formation of 30{\deg} faceted pits. The cone-like structures present Ga enrichment at the boundary facets and larger QDs within the defect. The bimodality is attributed to the differing dot size/composition within the defects and at the defect boundaries, which is confirmed by the correlation of microscopy results and Schr\"odinger-Poisson calculations.

Conventional ultraviolet (UV) lamps for disinfection emit radiation in the 255-270 nm range, which poses a high risk of causing cancer and cataracts. To address these concerns, solid-state far UV-C sources emitting below 240 nm are gaining attention as a safe and sustainable disinfection solution for occupied spaces. Here, we delve into the extension of the AlxGa1-xN/AlN quantum dot (QD) technology towards the far UV-C range, which presents various challenges associated with the reduction of the lattice mismatch and band offset when Al is incorporated in the QDs. We explore the structural and optical impact of increasing the Al content through the increase of the Al flux and eventual correction of the Ga flux to maintain a constant metal/N ratio. We also examine the impact of extreme miniaturization of the QDs, achieved through a reduction of their growth time, on the spectral behavior and internal quantum efficiency (IQE). The high Al content results in QDs with a reduced aspect ratio (height/diameter) and thicker wetting layer when compared to the GaN/AlN system. Self-assembled QDs grown with a metal/N ratio ranging from 0.5 to 0.8 show an IQE around 50%, independent of the Al content (up to 65%) or emission wavelength (300-230 nm). However, samples emitting at wavelengths below 270 nm exhibit a bimodal luminescence associated with inhomogeneous in-plane emission attributed to fluctuations of the QD shape associated with extended defects. Reducing the QD size exacerbates the bimodality without reducing the emission wavelength. The power efficiencies under electron beam pumping range from 0.4% to 1%, with clear potential for improvement through surface treatments that enhance light extraction efficiency.

By collecting simultaneously optical and chemical/morphological data from nanoscale volumes, the Photonic Atom Probe (PAP) can be applied not only to the study of the relationship between optical and structural properties of quantum emitter but also to evaluate the influence of other factors, such as the presence of point defects, on the photoluminescence. Through the analysis of multiple layers of InGaN/GaN quantum dots (QDs), grown so that the density of structural defects is higher with increasing distance from the substrate, we establish that the light emission is higher in the regions exhibiting a higher presence of structural defects. While the presence of intrinsic point defects with non-radiative recombination properties remains elusive, our result is consistent with the fact that QD layers closer to the substrate behave as traps for non-radiative point defects. This result demonstrates the potential of the PAP as a technique for the study of the optical properties of defects in semiconductors.

Transition metal dichalcogenides (TMDs) have received great attention over the past decade due to their wide range of optoelectronic properties and intrinsic compatibility with ultimately downsized devices (as ultrathin or even 2D layers), making them desirable for next-generation technologies. To obtain TMDs with satisfying optoelectronic properties, very high process or annealing temperatures are generally applied (above 550 degrees C), requiring a dedicated growth substrate followed by a mechanical transfer of the TMD layer onto the target device. Hexagonal tin(IV) disulfide (SnS2) and orthorhombic tin(II) monosulfide (SnS) are another class of layered semiconducting metal chalcogenides displaying n-type and p-type conduction, respectively. Unlike early-transition-metal TMDs, highly crystalline SnS2 and SnS layers can be grown at relatively low temperatures (below 400 degrees C), which make them more suited for direct implementation on integrated circuits. In this article, we demonstrate the relevance of volatile and nontoxic liquid organosulfur compounds as a safe and convenient alternative to both elemental sulfur and H2S for producing either SnS2 or SnS ultrathin layers with good crystallinity. Between 300 and 400 degrees C, atomic layer deposited SnO2 is directly converted into 2H-SnS2 by using tert-butyl disulfide (TBDS). If tert-butylthiol (TBT) is used, the alpha-SnS phase is obtained. At 250 degrees C, TBDS converts alpha-SnS into SnS2, and the zip mechanism allowing this transformation is analyzed at the atomic scale by using super-resolved transmission electron microscopy.

We report a correlative microscopy study of a sample containing three stacks of InGaN/GaN quantum dots (QDs) grown at different substrate temperature, each stack consisting of 3 layers of QDs. Decreasing the substrate temperature along the growth axis leads to the proliferation of structural defects. However, the luminescence intensity increases towards the surface, in spite of the higher density of threading dislocations, revealing that the QD layers closer to the substrate behave as traps for non-radiative point defects. During atom probe tomography experiments combined with in-situ micro-photoluminescence, it was possible to isolate the optical emission of a single QD located in the topmost QD stack, closer to the sample surface. The single QD emission line displayed a spectral shift during the experiment confirming the relaxation of elastic strain due to material evaporation during atom probe tomography.

The solid phase recrystallization of partially amorphized SOI structures using a pulsed Ultra-Violet Nanosecond Laser Annealing (UV-NLA) is reported. It is shown that combining UV-NLA process with a heating chuck at low temperature (450 °C) results in the perfect recrystallization of the amorphized portion of the silicon layer. Actually, sub-melt multi-pulse UV-NLA enables obtaining the total crystal recovery and a very high dopant activation rate, comparable to melt laser annealing approaches or high temperature rapid thermal annealing, with a very low overall thermal budget. This approach is a great alternative to traditional solid phase epitaxial regrowth process, which reach it limits, in terms of recrystallization rate, at temperatures lower than 500 °C. The process presented here is thus suitable for integration paths in which the thermal budget must be limited as for example 3D sequential integration. Besides the high activation rate, another benefit of the solid phase recrystallization, compared to an equivalent laser anneal in the melt regime, is the almost unchanged surface roughness. Furthermore, the use of an in-situ metrology based on Time Resolved Reflectometry (TRR) enables the monitoring of the crystalline seed thickness evolution during UV-NLA and the estimation of the recrystallization rate.

The full InGaN structure was grown on two different InGaNOS substrates from Soitec. An electron blocking layer was inserted in the full InGaN light emitting diode (LED). Enhanced internal quantum efficiency of red emitting InGaN/InGaN quantum wells was measured with a value above 10% at 640 nm. 10 μm diameter circular micro-LEDs are emitted at 625 nm with an external quantum efficiency of 0.14% at 8 A cm−2 with an estimated light extraction efficiency below 4%. With a a lattice parameter of 3.210 Å, InGaN based red LED can also emit up to 650 nm.

3D analysis of an arsenic-doped silicon fin sample is performed in a transmission electron microscope (TEM). High angle annular dark-field scanning TEM (STEM-HAADF) and energy-dispersive x-ray spectroscopy (STEM-EDX) modes are used simultaneously to extract 3D complementary multi-resolution information about the sample. The small pixel size and angular step chosen for the STEM-HAADF acquisition yield reliable information about the sidewall roughness and the arsenic clusters’ average volume. The chemical sensitivity of STEM-EDX tomography gives insights into the 3D conformality of the arsenic implantation and its depth distribution. Non-negative matrix factorization method is employed to identify the chemical phases present in the sample automatically. A total variation minimization algorithm, implemented in 3D, produces high-quality volumes from heavily undersampled datasets. The extension of this correlative approach to electron energy-loss spectroscopy STEM tomography and atom probe tomography is also discussed.