Epitaxial Growth of Boron Carbide on 4H-SiC

In this work, the successful heteroepitaxial growth of boron carbide (B x C) on 4HSiC(0001) 4{\textdegree} off substrate using chemical vapor deposition (CVD) is reported. Towards this end, a two-step procedure was developed, involving the 4H-SiC substrate boridation under BCl 3 precursor at 1200{\textdegree}C, followed by conventional CVD under BCl 3 + C 3 H 8 at 1600{\textdegree}C. Such a procedure allowed obtaining reproducibly monocrystalline (0001) oriented films of B x C with a step flow morphology at a growth rate of 1.9 $\mu$m/h. Without the boridation step, the layers are systematically polycrystalline. The study of the epitaxial growth mechanism shows that a monocrystalline B x C layer is formed after boridation but covered with a B-and Si-containing amorphous layer. Upon heating up to 1600{\textdegree}C, under pure H 2 atmosphere, the amorphous layer was converted into epitaxial B x C and transient surface SiB x and Si crystallites. These crystallites disappear upon CVD growth

Formation de macromarches sur substrat 4H-SiC via la fusion de silicium dans une configuration sandwich

International audienceWith a view to designing a homogeneous and controlled step-bunched morphology on large monocrystalline 4H-SiC(0001) surfaces, a sandwich configuration was investigated. A piece of silicon was melted between two 4H-SiC 4° off wafers, allowing a better spreading of the liquid than with a Si drop approach. Using as low liquid Si thickness as 30 µm, homogeneously highly stepbunched surfaces were obtained, though with irregular step shapes. This was found to be the result of time dependent dissolution of the SiC-bottom wafer under the natural vertical thermal gradient of the setup. The most parallel step and terrace structures were generated using 400 µm thick liquid Si though this led to long range inhomogeneities associated with complex mass transport. The proposed mechanism includes the combined effect of H2 etching at the edges acting as C pump and electromagnetic convection rolls for long range transport of these dissolved C atoms

Exploring SiC Growth Limitation of Vapor-Liquid-Solid Mechanism when Using Two Different Carbon Precursors

International audienceIn this paper, conditions for obtaining high growth rate during epitaxial growth of SiC by vapor-liquid-solid mechanism are investigated. The alloys studied were Ge-Si, Al-Si and Al-Ge-Si with various compositions. Temperature was varied between 1100 and 1300°C and the carbon precursor was either propane or methane. The variation of layers thickness was studied at low and high precursor partial pressure. It was found that growth rates obtained with both methane and propane are rather similar at low precursor partial pressures. However, when using Ge based melts, the use of high propane flux leads to the formation of a SiC crust on top of the liquid, which limits the growth by VLS. But when methane is used, even at extremely high flux (up to 100 sccm), no crust could be detected on top of the liquid while the deposit thickness was still rather small (between 1.12 μm and 1.30 μm). When using Al-Si alloys, no crust was also observed under 100 sccm methane but the thickness was as high as 11.5 µm after 30 min growth. It is proposed that the upper limitation of VLS growth rate depends mainly on C solubility of the liquid phase

Growth of Nanocrystalline Translucent h-BN Films Deposited by CVD at High Temperature on SiC Substrates

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Growing 3C-SiC heteroepitaxial layers on α-SiC substrate by vapour–liquid–solid mechanism from the Al–Ge–Si ternary system

International audienceIn this work, we present and compare the results obtained from different Si-based melts (Ge–Si, Al–Si and Al–Ge–Si) for growing SiC layers on α-SiC substrate by vapour–liquid–solid (VLS) mechanism. It was found that, depending on melt composition, the deposit could be either a complete 3C or α-SiC layer or even a mixture of these polytypes. The binary Al–Si melt leads systematically to a highly p-type homoepitaxial α-SiC deposit while Ge–Si melt gives a non-intentional n-type doped layers of either 3C or 6H polytypes depending on growth conditions. However, highly p-type doped 3C heteroepitaxial deposit can be obtained if a small amount of Al is added to the Ge–Si binary liquid phase. This means that the VLS mechanism is very flexible and allows growing either n- or p-type SiC layers of 3C or 6H polytypes

Investigation of 3C-SiC(111) Homoepitaxial Growth by CVD at High Temperature

International audienceStarting from 3C-SiC(111) layers grown by Vapour-Liquid-Solid mechanism, homoepitaxial growth by Chemical Vapour Deposition was carried out on top of these seeds. The effect of the growth temperature and of the C/Si ratio in the gas phase was investigated on the surface morphology, the roughness and the defect density. It was found that the initial highly step-bunched surface of the VLS seeds could be greatly smoothen using appropriate conditions. These conditions were also found to reduce significantly the defect size and/or density at the surface

Propriétés thermochromiques de quelques matériaux oxydes colorés

International audienceThe thermochromic properties up to 500°C of some colored, commercial and non-toxic oxides were studied. It includes Bi 2 O 3 , Fe 2 O 3 , In 2 O 3 , WO 3 , Er 2 O 3 , YAG:Ce (Ce doped yttrium aluminum garnet Y 3 Al 5 O 12) and YInMn-Blue (Mn doped yttrium indium oxide YInO 3). From the CIELAB colorimetric parameters (L*a*b*), evolution of the color contrast ΔE with temperature was calculated. It allowed estimating that most of these oxides change color reversibly with increasing temperature. Two exceptions were identified: i) Er 2 O 3 which stayed almost identically pink on all the temperature range and ii) WO 3 which original color was not recovered upon cooling back to room temperature. While the color change of the other oxides was gradual with increasing temperature, YAG:Ce compound behaved differently since its thermochromicity abruptly started above 300°C. The obtained datasets for all these compounds can be used for anticipating the thermochromic properties of these powders and the blends made out of them

Deposition of nanocrystalline translucent h-BN films by chemical vapor deposition at high temperature

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3C-SiC Heteroepitaxial Layers Grown on Silicon Substrates with Various Orientations

International audienceThis work investigates the 3C-SiC heteroepitaxial growth on silicon substrates having a wide variety of orientations, i.e. (100) on axis and 2°off, (111), (110), (211), (311), (331), (510), (553) and (995). All the 3C-SiC layers were grown using the same two-step CVD process with a growth rate of 2 µm/h. According to X-ray diffraction characterizations, direct heteroepitaxy (layer having exactly the same orientation as the substrate) was successful on most of the Si substrates except for (110) one which was the only orientation leading to obvious polycrystalline deposit. Each layer led to a specific surface morphology, the smoothest being the ones grown on Si(100)2°off, and (995) substrates. None of these layers cracked upon cooling though those grown on Si(111), (211) and (553) substrates were highly bowed

Elimination of twin boundaries when growing 3C-SiC heteroepitaxial by vapour-liquid-solid mechanism on patterned 4H-SiC substrate

International audienceIn this work we report on the study of twin boundary (TB) evolution during heteroepitaxial growth of 3C-SiC on patterned 4H-SiC(0001) substrate by vapour-liquid-solid (VLS) mechanism. Ge 50Si 50 melt was used at a temperature of 1450°C. 3C-SiC deposit was obtained on top and outside the mesas. Some lateral enlargement of these mesas was observed but it was systematically homoepitaxial. Elimination of TBs inside the 3C-SiC deposit on top of the mesas was observed for specific mesa shape and/or orientation of the sidewalls. Though three-fold or six-fold symmetry mesas are recommended for TB elimination, originally circular mesas lead also to the same result due to initial faceting toward hexagonal shape