Didier Chaussende

Characterization and modelling of the ion-irradiation induced disorder in 6H-SiC and 3C-SiC single crystals

6H-SiC and 3C-SiC single crystals were simultaneously irradiated at room temperature with 100 keV Fe ions at fluences up to 4 × 1014 cm−2 (~0.7 dpa), i.e. up to amorphization. The disordering behaviour of both polytypes has been investigated by means of Rutherford backscattering spectrometry in the channelling mode and synchrotron x-ray diffraction. For the first time, it is experimentally demonstrated that the general damage build-up is similar in both polytypes. At low dose, irradiation induces the formation of small interstitial-type defects. With increasing dose, amorphous domains start to form at the expense of the defective crystalline regions. Full amorphization of the irradiated layer is achieved at the same dose (~0.45 dpa) for both polytypes. It is also shown that the interstitial-type defects formed during the first irradiation stage induce a tensile elastic strain (up to ~4.0%) with which is associated an elastic energy. It is conjectured that this stored energy destabilizes the current defective microstructure observed at low dose and stimulates the formation of the amorphous nanostructures at higher dose. Finally, the disorder accumulation has been successfully reproduced with two models (namely multi-step damage accumulation and direct-impact/defect-stimulated). Results obtained from this modelling are compared and discussed in the light of experimental data.

Large area quasi-free standing monolayer graphene on 3C-SiC(111)

Large scale, homogeneous quasi-free standing monolayer graphene is obtained on cubic silicon carbide, i.e., the 3C-SiC(111) surface, which represents an appealing and cost effective platform for graphene growth. The quasi-free monolayer is produced by intercalation of hydrogen under the interfacial, (6 root 3 x 6 root 3)R30 degrees-reconstructed carbon layer. After intercalation, angle resolved photoemission spectroscopy reveals sharp linear pi-bands. The decoupling of graphene from the substrate is identified by x-ray photoemission spectroscopy and low energy electron diffraction. Atomic force microscopy and low energy electron microscopy demonstrate that homogeneous monolayer domains extend over areas of hundreds of square-micrometers

Revealing the electronic band structure of trilayer graphene on SiC: An angle-resolved photoemission study

In recent times, trilayer graphene has attracted wide attention owing to its stacking and electric-field-dependent electronic properties. However, a direct and well-resolved experimental visualization of its band structure has not yet been reported. In this paper, we present angle-resolved photoemission spectroscopy data which show with high resolution the electronic band structure of trilayer graphene obtained on alpha-SiC(0001) and beta-SiC(111) via hydrogen intercalation. Electronic bands obtained from tight-binding calculations are fitted to the experimental data to extract the interatomic hopping parameters for Bernal and rhombohedral stacked trilayers. Low-energy electron microscopy measurements demonstrate that the trilayer domains extend over areas of tens of square micrometers, suggesting the feasibility of exploiting this material in electronic and photonic devices. Furthermore, our results suggest that, on SiC substrates, the occurrence of a rhombohedral stacked trilayer is significantly higher than in natural bulk graphite. (Less)

Continuous Feed Physical Vapor Transport Toward High Purity and Long Boule Growth of SiC

A new reactor concept for the growth of silicon carbide bulk crystals and/or thick epitaxial layers is presented. A coupled approach involving process modeling and numerical simulation and experimental results and characterization was used. This new process combines both high-temperature chemical vapor deposition (HTCVD) for continuous feeding of the polycrystalline source and physical vapor transport (PVT) for single-crystal growth. A special crucible design was built to perform both steps simultaneously. For the feeding step (HTCVD), tetramethylsilane diluted in argon was used. The typical growth rate obtained by the continuous feed PVT process is 100 μm/h at 1900°C. The growth of thick epitaxial layers is demonstrated with a pure two-dimensional growth regime.

A comprehensive study of SiC growth processes in a VPE reactor

Abstract We performed an experimental study of the effect of the gas phase composition on the growth mechanism of 3C-SiC on Si(100) by atmospheric-pressure vapour phase epitaxy at 1350°C. Silane and propane diluted in hydrogen were used as precursors for the growth. We demonstrate the existence of an equilibrium partial pressure of carbon above the growing surface, which ensures a mirror-like morphology. For too low a carbon partial pressure (C/Si ratio in the gas phase lower than 2.7 with a growth rate of 3 μm h −1 ), the layer morphology and crystalline quality quickly degrade. For too high a carbon partial pressure (C/Si ratio higher than 5 with the same growth rate), SiC clusters form on the growing layers. We propose a mechanism of formation for these clusters taking into account the interactions between the C and Si species in the hot boundary layer.

Raman scattering from Ti3SiC2 single crystals

The lack of single crystalline Ti3SiC2 samples is currently limiting the accurate measurement of its basic properties as its layered crystalline structure presents a very strong anisotropy. In this letter, we report the growth of pure Ti3SiC2 single crystals after a careful study of the Ti3SiC2 liquidus surface extent through thermodynamical calculations. From a Raman scattering study on those single crystals, an unambiguous assignment of most of the phonon modes has been established, giving an answer to the discrepancies existing in the literature.

Status of SiC bulk growth processes

The present paper gives an overview of the different routes to grow SiC single crystals. The focus is put on the new emerging processes compared with the well established ones. A review of the process engineering modelling is given. Finally, some selected results are pointed out as they should be considered for the future development of SiC material.

X-ray diffuse scattering from stacking faults in thick 3C-SiC single crystals

Stacking faults in thick (001)- and (111)-oriented 3C-SiC single crystals are studied by high resolution x-ray diffraction. The authors demonstrate that the analysis of the diffuse scattering intensity distribution can be used as a nondestructive means to accurately determine the densities of Shockley-type stacking faults. The diffuse scattering intensity is simulated with a scattering model based on a difference-equation description of faulting in fcc materials. It is shown that the (001) SiC crystals exhibit an anisotropic fault distribution, whereas the (111) SiC crystals exhibit an isotropic fault distribution, in excellent quantitative agreement with transmission electron microscopy observations.

Large Area DPB Free (111) β-SiC Thick Layer Grown on (0001) α-SiC Nominal Surfaces by the CF-PVT Method

Thick (111) oriented β-SiC layers have been grown by hetero-epitaxy on a (0001) a-SiC substrate with the Continuous Feed-Physical Vapour Transport (CF-PVT) method. The growth rate was 68 µm/h at a pressure of 2 torr and a temperature of 1950°C. The nucleation step of the β-SiC layer during the heating up of the process was studied in order to manage first the a to b heteropolytypic transition and second the selection of the b-SiC orientation. With a adapted seeding stage, we grew a 0.4mm thick layer almost free of Double Positioning Boundaries on a 30mm diameter sample. First observations of the layer by cross-polarised optical Microscopy are presented both in planar view and in cross section geometry.

Study of the interaction between graphite and Al-Si melts for the growth of crystalline silicon carbide

The chemical interaction between Al-Si melts of different compositions and graphite was investigated in order to clarify the mechanism of spontaneous growth of silicon carbide crystals from these melts. Calibrated graphite small rods were used as carbon source to facilitate comparison between experiments. For a temperature set to 1100°C, the reaction time and Si content of the melt were varied from 1 to 48 hours and 20 to 40 at.%, respectively. It has been found that in a first stage the liquid reacts at a relatively slow rate to form a microcrystalline SiC layer around the graphite rod. When this SiC layer has reached a certain thickness, a violent attack follows in some specific sites by rapid dissolution of the rod. Radial liquid channels progress from the surface of the rod up to its centre and then total conversion of graphite into SiC rapidly occurs. The local Si content of the melt, which controls the carbon solubility in the liquid, governs the overall mechanism. To form faceted β-SiC crystals, the growth mechanism should involve carbon dissolution in one place and supersaturation in another place in relation with local changes of the Si content in the melt.