Starting 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.

Like on 6H-SiC substrates, 3C-SiC islands precipitation was found to be the initial stage of the VLS growth of 3C-SiC layers on 4H-SiC surfaces. This precipitation happens between 1100 and 1200°C with a heating rate of 2.8°C.s-1, without addition of propane. The islands size increases in a similar manner whether the final temperature increases (for a given heating rate) or the heating rate decreases (for a given final temperature). This enlargement can give rise to a complete cubic layer for the highest temperatures or the slowest heating rates. It is suggested that the carbon atoms involved in the enlargement process (after the nucleation) come from the graphite crucible.

6H and 4H–SiC epilayers were Al-implanted at room temperature with multiple energies (ranging from 25 to 300 keV) in order to form p-type layers with an Al plateau concentration of 4.5×1019 cm-3 and 9×1019 cm-3. Post-implantation annealing were performed at 1700 or 1800 °C up to 30 min in Ar ambient. During this process, some samples were encapsulated with a graphite (C) cap obtained by thermal conversion of a spin-coated AZ5214E photoresist. From Atomic Force Microscope measurements, the roughness is found to increase drastically with annealing temperature for unprotected samples while the C capped samples show a preservation of their surface states even for the highest annealing temperature. After 1800°C/30 min annealing, the RMS roughness is 0.46 nm for the lower fluence implanted samples, slightly higher than for unimplanted samples (0.31 nm). Secondary Ion Mass Spectroscopy measurements confirm that the C cap was totally removed from the SiC surface. The total Al-implanted fluence is preserved during postimplantation annealing. A redistribution of the Al dopants is observed at the surface which might be attributed to Si vacancy-enhanced diffusion. An accumulation peak is also observed after annealing at 0.29 9m, depth corresponding to the amorphous/crystalline interface that was determined on the as-implanted samples by Rutherford Backscattering Spectroscopy in channeling mode. The redistribution of the dopants has an impact on their electrical activation. A lower sheet resistance (Rsh= 8 k) is obtained for samples annealed without capping than for samples annealed with C capping (Rsh= 15 k ).

Epitaxial 3C-SiC(111) films were grown on 6H-SiC(0001) Si face on axis substrates by chemical vapor deposition under H2, SiH4 and C3H8 in a cold wall vertical reactor. Two temperatures were studied (1450 and 1700°C) with various C/Si ratio and deposition time. It was found that under conditions giving high lateral growth (low C/Si and/or high temperature), homoepitaxial growth occurred even at temperatures as low as 1450°C. For other conditions, the 3C-SiC polytype was detected and always together with the formation of double positioning boundaries whose density was found to depend on the growth conditions but not on the initial surface reconstruction. Single domain enlargement was observed when growth was performed at 1700°C over a nucleation layer grown at 1450°C.

In this paper, we present a study of the surface preparation of on-axis, Si face 6H–SiC(0001) and 4H–SiC(0001) substrates for the growth of 3C–SiC heteroepitaxial layers. The treatments were performed in a vertical cold-wall reactor, at temperatures ranging from 1350 to 1650°C for 10–30min, under H2 or H2+C3H8 atmospheres. By atomic force microscopy investigation, the 4H–SiC surfaces were always found to be rougher than the 6H–SiC ones so that we mainly studied the use of 6H–SiC. All the samples displayed a more or less regular surface covered with small steps (up to 1nm height). Si droplet formation was observed in some specific conditions, which, hence, are to be avoided. The most regular array of steps (∼0.7nm height) was obtained on 6H–SiC seeds under H2 treatment at 1450°C for 10min. On such surfaces, 3C–SiC growth was performed using a mixture of SiH4+C3H8 at 1450°C with a C/Si ratio of 3 in the gas phase.

We report on the effect of the arsenic precursor and growth temperature on atomic ordering of InGaAs alloy nearly lattice-matched to InP grown by metalorganic vapor phase epitaxy. The optical properties, microstructure and surface morphologies show that the samples grown at 570–600 °C with the trimethylarsenic have some characteristic features: (i) a strong power-dependent redshift of the photoluminescence peak position relative to the band-gap; (ii) the presence of CuPt ordered structures as seen by high resolution transmission electron microscopy and transmission electron diffraction pattern; and (iii) a high surface density of islands as observed by atomic force microscopy. Ordering is seen for trimethylarsenic-grown epilayers up to 600 °C growth temperature, while it is not observed for arsine-grown epitaxial layers at the same growth temperature. A link between the surface morphology and the underlying chemical order as a result of the surface processes leading to the chemical ordering for trimethylarsenic-grown epilayers is discussed.

We compare two series of 4H-SiC layers grown with either silane/propane or hexamethyldisilane/propane precursor systems. In both cases, the growth rate increases with precursor flow. However it saturates and, then, tend to decrease at high temperature. The range of growth conditions (C/Si ratio, growth rate, growth temperature) which give good surface morphology has been studied. The operating windows are identical for the two systems In both cases, micro-Raman and LTPL spectroscopy confirm the formation of high quality 4H-SiC polytype.

En The MOVPE growth of the BgaAs alloy with the influence of the boron gas phase composition Xv is reported followed by a thermodynamical approach. The incorporation behavior of boron into GaAs is complex as the rate of incorporation is highly non linear with Xv. Due to the lack of available thermodynamical data for Bas, we proposed by extrapolation to determine the order of magnitude for the enthalpy of formation and Gibbs free energy values of the alloy. Our approach is based on the comparison of the trend between several series in different systems (BP, BN, AlAs, GaAs). The calculation yields the boron partial pressure PB being much lower than PGa. The alloy content is controlled by the Ga equilibrium partial pressure. A surface segregation of boron is due to several factors such as a high vapor supersaturation needed during growth or a complex phase diagram.

From a comparative evaluation of hexamethyldisilane (HMDS) and silane-propane (SP) precursor systems, it is shown that HMDS needs a small addition of propane to deposit heteroepitaxial layers of 3C-SiC on Si with superior crystalline properties. In this case, propane compensates for the secondary reactions induced by hydrogen reacting with carbon. Using atmospheric pressure CVD conditions, the new system (HMDS-propane) demonstrates several advantages. It is safer to handle than SP and allows a higher growth rate (up to 7 mum/h at 1350degreesC) without any degradation of the layer morphology. However, lowering the deposition temperature, HMDS has been found more stable than silane. This is opposite to most standard belief but explains why, in this case, a high temperature step (similar to1350degreesC) is always necessary to grow high quality material.

Coherent InAs islands separated by GaAs spacer (d) layers are shown to exhibit self-organized growth along the vertical direction. A vertically stacked layer structure is useful for controlling the size distribution of quantum dots. The thickness of the GaAs spacer has been varied to study its influence on the structural and optical properties. The structural and optical properties of multilayer InAs/GaAs quantum dots (QDs) have been investigated by atomic force microscopy (AFM), transmission electron microscopy (TEM), and photoluminescence (PL) measurements. The PL full width at half maximum (FWHM), reflecting the size distribution of the QDs, was found to reach a minimum for an inter-dots GaAs spacer layer thickness of 30 monolayers (ML). For the optimized structure, the TEM image shows that multilayer QDs align vertically in stacks with no observation of apparent structural defects. Furthermore, AFM images showed an improvement of the size uniformity of the QDs in the last layer of QDs with respect to the first one. The effect of growth interruption on the optical properties of the optimized sample (E30) was investigated by PL. The observed red shift is attributed to the evolution of the InAs islands during the growth interruption. We show the possibility of increasing the size of the QDs approaching the strategically important 1.3 μm wavelength range (at room temperature) with growth interruption after InAs QD deposition.

Combinations of meso-, macro- and microporous coatings with a chemical composition of 90%Al2O3-10%SiO2 were elaborated on SiC Hi-Nicalon fibers using the sol-gel process. They were evaluated as porous interphase for the reinforcement of CMC. The mesoporous oxide, in contact with the fiber, allows cracks deviation whereas the macroporous one, in contact with the matrix, avoids the gaseous infiltration of the mesopores during the SiC CVD matrix process. It also prevents from oxygen diffusion during high temperature under air. The characterization of the composites was performed by SEM (scanning electron microscopy), TEM (transmission electron microscopy), X-ray diffraction, and EDS (energy dispersive spectrometry). TEM evidenced the porosity gradient as expected. A tensile test on the composites revealed brittle behavior (fracture) and no fiber debonding was observed.

From a comparative evaluation of hexamethyldisilane (HMDS) and silane–propane (SP) precursor systems, it is shown that HMDS needs a small addition of propane to deposit heteroepitaxial layers of 3C–SiC on Si with superior crystalline properties. In this case, propane compensates for the secondary reactions induced by hydrogen reacting with carbon. Using atmospheric pressure chemical vapour deposition conditions, the new system (HMDS–propane) demonstrates several advantages. It is safer to handle than SP and allows a higher growth rate (up to 7 µm h−1 at 1350 °C) without any degradation of the layer morphology. However, when lowering the deposition temperature, HMDS is revealed to be more stable than silane. This is in contrast to most standard beliefs but explains why a high temperature (∼1350 °C) is always necessary to grow high-quality material using HMDS.

In a first step towards the growth of BInGaAs, we have grown and characterized the BxGa1−xAs/GaAs ternary compound with boron composition up to x=0.06 on GaAs(0 0 1) vicinal substrates. The incorporation behavior of boron has been studied as a function of growth temperature, diborane flux, gallium precursor and carrier gas (hydrogen and nitrogen). A maximum for boron incorporation (x≈0.04–0.06) is found at 550–600°C depending on the precursor and the carrier gas. The epilayers have good crystalline quality as measured by X-ray rocking curve of the (0 0 4) diffraction peak (full-width at half-maximum of 38 arcsec for x=0.035). However, the surface morphology is very sensitive to the diborane supersaturation in the gas phase. At high diborane flow rate, the surface appears as though it is covered in dust. A low surface roughness of 0.4 nm was measured by atomic force microcopy (AFM) in the best growth conditions. AFM images also show a cross-hatch pattern for the highest boron composition.

We have investigated the growth, the microstructure and the optical properties of the GaAs0.97N0.03/GaAs interface. Epilayers were grown at 520–550°C using trimethylgallium, dimethylhydrazine and arsine on GaAs(001) vicinal surfaces. A 5–6nm thick layer of GaAsN with N-enrichment is clearly seen by cross-sectional transmission electron microscopy at the interfacial region. The nitrogen composition at the interface is twice that of the bulk epilayer (close to 1.6%) as shown by photoluminescence spectroscopy (PL) and high resolution X-ray diffraction. The PL data of several samples shows two peaks located at 1–1.1 and 1.2–1.3eV associated with the interfacial region and the bulk layer, respectively. We discuss several mechanisms for the nitrogen enrichment by comparing the GaAsN film thickness. The step/terrace surface morphology of GaAs before growth is probably the key parameter.

4H-SiC seeds have been treated at high temperatures (1650–1900°C) under Ar or N2 in a sublimation like graphite crucible with SiC powder at the hotter part. It was found that the surface morphology is significantly altered by the nature of the atmosphere. Surfaces without step bunching under 1bar of N2 appear for low temperature range (≤1700°C) whereas at higher temperature or lower pressure a step bunch morphology appears. Ar always gives step bunched surfaces but with more regular and parallel steps. Thermodynamical calculations performed on the SiCN (Ar) system show that N2 plays an important role on the gas phase chemistry of decomposition of SiC by forming gaseous species of nitrides. The theoretical results correlate well with the observations of surface morphology and graphitisation of the SiC powder.

The behavior of boron incorporation into GaAs has been studied by x-ray photoelectron spectroscopy, x-ray diffraction, and atomic force microscopy. As the boron content of the film was increased, both the characteristic peak for the B 1s core level at 188 eV and As Auger transition (260 eV) could be detected by XPS. At 550–600 °C, single crystalline films could only be grown for x⩽0.06. Upon increasing the diborane flux in the gas phase, the film stoichiometry and the boron surface composition evolved rapidly towards a boron-rich subarsenide compound. This trend is followed by a clear degradation of the surface morphology and an increase in the surface roughness. A surface segregation of boron is suggested due to the high diborane vapor supersaturation needed during growth.

4H-SiC seeds have been treated at high temperature (1650-1900degreesC) under Ar or N-2 in a sublimation like graphite crucible with SiC powder at the hotter part. It was found that the surface morphology is significantly altered by the nature of the atmosphere. N-2 gives a smoother surface for the low temperature range (<1700degreesC) whereas at higher temperature it degrades compared to Ar. Thermodynamical calculations performed on the Si-C-N (Ar) system show that N-2 plays an important role on the gas phase chemistry of decomposition of SiC by forming gaseous species of nitrides. It is found that the gas phase is C rich when N-2 is used at low temperature whereas it becomes Si rich at a temperature higher than 1700degreesC. The theoretical results correlate well with the graphitisation of the SiC powder.

HMDS has been compared to the silane/propane system for the homoepitaxy of 4H-SiC in the growth temperature range from 1450degreesC to 1600degreesC. It was found that HMDS leads to a growth rate as high as 7 mum/h but with a lower growth efficiency compared to silane/propane. The layers grown with HMDS have good properties (AFM roughness, impurities level) comparable to that obtained with the silane/propane system.