Defects and polytypism in SiC : the role of diffuse X-ray scattering

International audienceStacking faults (SFs) and the 3C‐6H polytypic transition in thick (001)‐oriented 3C‐SiC crystals are studied by means of diffuse X‐ray scattering. The presence of SFs lying in the {111} planes gives rise to streaked reciprocal lattice points with the streaks being parallel to the directions. In the case of low SF densities the defects are uncorrelated and the simulation of the diffuse intensity distribution allows to derive the SF density. In partially transformed crystals, the SFs are spatially correlated which gives rise to an intense and asymmetric diffuse scattering distribution. Its simulation allows to determine both the transformation mechanism and the transformation level

Polytypic transformations in SiC: Diffuse x-ray scattering and Monte Carlo simulations

International audienceSolid-state phase transitions in SiC are investigated using diffuse x-ray scattering andMonte Carlo simulations. As an example, the 3C-6H transformation is investigated in detail. The transformation is modeled with a statistical algorithm based on the concept of double cross-slipping and subsequent dissociation of basal plane dislocations. The corresponding diffuse x-ray scattering curves are calculated and quantitatively compared with experimental data obtained from 3C-SiC crystals annealed at high temperatures (1700-2100◦ C). From the simulations, it is demonstrated that the transformation implies the multiplication and ordering of double and triple stacking faults (SFs). The transformation level and root-mean-squared strains associated with the dislocations are determined from the simulations. The defect structure formed during the transition can be rationalized by considering the relative energies of the SFs. Using an axial next-nearest-neighbor Ising interaction model we show that single SFs are not energetically favored, whereas the simultaneous occurrence of double and triple SFs implies that their relative energy difference remains below a critical value (∼8-9%)

Study of the stability of 3C-SiC single crystals using high resolution diffuse X-ray scattering

International audienceThe stability of (001)‐oriented 3C silicon carbide crystals is studied by a method coupling high resolution x‐ray diffraction and numerical simulations. The analysis of the diffuse scattering intensity distribution along selected directions in reciprocal space allows us to obtain qualitative and quantitative informations regarding the 3C‐6H transition. Our latest results concerning the influence of the initial crystal quality (presence of defects) and of annealing time on the 3C‐6H transition are presented in this article

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

International audience6H-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

Nondestructive Evaluation of Photo-Electrical Properties of 3C-SiC (111) Homoepitaxial Layers Grown by CVD

International audienceFree carrier absorption (FCA) and picosecond light-induced transient grating (LITG) techniques were applied to study the photoelectrical properties of 3C-SiC(111) homoepitaxial layers grown by CVD method on VLS (vapour-liquid-solid) grown seeds. The thickness of the CVD layers was ~10.5 µm with non-intentional type doping of n (~ 1017 cm-3) or p (<1015 cm-3). The carrier lifetime and the diffusion coefficient were measured as the function of the sample temperature, the injected excess carrier density at different growth parameters. At room temperature the ambipolar diffusion coefficient was Da=2.5-3 cm2/s, while the lifetime was in the range of 12-18 ns. The best structural and electrical properties were obtained for a CVD layer grown at high, 1600 °C temperature

On the stability of 3C-SiC single crystals at high temperatures

International audienceThe 3C-6H polytypic transition in 3C-SiC single crystals is studied by means of diffuse X-ray scattering (DXS) coupled with transmission electron microscopy (TEM). TEM reveals that the partially transformed SiC crystals contain regions of significantly transformed SiC (characterized by a high density of stacking faults) co-existing with regions of pure 3C-SiC. The simulation of the diffuse intensity allows to determine both the volume fraction of transformed material and the transformation level within these regions. It is further shown that the evolution with time and temperature of the transition implies the multiplication and glide of partial dislocations, the kinetics of which are quantified by means of DXS