M. Lancin

30° Si(g) partial dislocation mobility in nitrogen-doped 4H-SiC

Well-controlled population of dislocations are introduced in 4H-SiC by bending in cantilever mode and annealing between 400 and 700°C. The introduced defects consist of double stacking faults, each bound by a pair of 30° Si(g) partial dislocations, and the expansion of which is asymmetric. The velocity of each individual 30° Si(g) pair is directly measured as a function of stress and temperature on the surface of samples etched after deformation. The activation energies of the 30° Si(g) partial dislocation pairs are strongly stress dependent, ranging between 1.25 and 1.7eV. These values are lower than the ones derived from plasticity experiments. This is probably because 30° Si(g) pairs and double stacking faults are generated in N-doped 4H-SiC (N=2×1018cm−3), with their development being promoted by quantum well action.Well-controlled population of dislocations are introduced in 4H-SiC by bending in cantilever mode and annealing between 400 and 700°C. The introduced defects consist of double stacking faults, each bound by a pair of 30° Si(g) partial dislocations, and the expansion of which is asymmetric. The velocity of each individual 30° Si(g) pair is directly measured as a function of stress and temperature on the surface of samples etched after deformation. The activation energies of the 30° Si(g) partial dislocation pairs are strongly stress dependent, ranging between 1.25 and 1.7eV. These values are lower than the ones derived from plasticity experiments. This is probably because 30° Si(g) pairs and double stacking faults are generated in N-doped 4H-SiC (N=2×1018cm−3), with their development being promoted by quantum well action.

Defects created in N-doped 4H-SiC in the brittle regime: Stacking fault multiplicity and dislocation cores

Defects introduced in N-doped 4H-SiC by surface scratching and bending at 823 K or 973 K were characterised by weak beam-dark field transmission electron microscopy (TEM), high-resolution TEM (HRTEM), large-angle convergent beam electron diffraction (LACBED), image analysis and dislocation core reconstructions. They consist of double stacking faults (DSFs) dragged by partial dislocation (PD) pairs in planes in which the Si–C dumbbells have the same orientation. The PDs forming a pair always have the same Burgers vectors. The reconstructions prove that their core composition depends on the dislocation character, the expansion direction and the orientation of the dumbbells in the glide planes. Only Si(g) are mobile, the lack of mobility of C(g) explaining why only three kinds of half-loops expand and why one DSF is always edged by two identical PDs. It is shown that the line morphology is not a sufficient criterion to determine the core composition. Although mechanical stresses were applied, additional thermodynamic and/or electronic driving forces influenced the DSF formation in our experiments.

Gettering of Diffused Au and of Cu and Ni Contamination in Silicon by Cavities Induced by High Energy He Implantation

Silicon samples were gold-diffused at different temperatures (870-950°C) and implanted with He ions at 1.6 MeV and fluences ranging from 2 × 10 16 up to 10 17 cm -2 . The implantation induced defects observed by conventional and high resolution cross section electron microscopy were found to be essentially cavities 10 to 100 nm in size which are faceted mainly along {111}, but also along {110} and {100} planes. The cavities are located at the sample depth predicted by the transport range of ions in matter simulation. Secondary ion mass spectroscopy profiles exhibit a shouldered shape with a maximum at the projected range. They demonstrate that the cavities are very efficient sinks for Au atoms; the shoulder of the profile could be related to the presence of smaller cavities and dislocations in the vicinity of the projected range. Gold concentration in the cavity area was below the detection limit of the energy dispersive spectroscopy technique, but both Cu and Ni contamination gave rise to silicides and could be chemically analysed. Cu 3 Si precipitates have grown in cavities as already reported in the literature, while NiSi 2 precipitates were observed for the first time in cavities.

Comparative study of the microstructure of the interphases in two SiC fibre/lithium aluminosilicate matrix composites

Abstract The microstructure of the interfacial region in two Nicalon SiC fibre/lithium aluminosilicate glass (with and without Nb2O5) matrix composites (which consists of a carbon layer and possibly NbC crystals) has been investigated by high-resolution electron microscopy. Special attention has been paid to the evolution of this microstructure from the matrix to the fibre. The study has revealed new data which have improved the understanding of these materials. The formation of the carbon layer begins at the surface of the glass and continues on the side of the fibre. A certain amount of carbon diffuses inside the matrix with a heterogeneous distribution. The addition of Nb2O5 to the glass results in the formation of a carbon layer with a more amorphous structure. An important feature has been revealed in the composite without Nb2O5 which contributes to its brittleness.

Structural characterization of 6H- and 4H-SiC polytypes by means of cathodoluminescence and x-ray topography

The cathodoluminescence (CL) technique is used to analyse the radiative recombination properties of four distinct silicon carbide (SiC) samples: a 6H-SiC n+-type Lely wafer, two off-axis 4H-SiC epitaxial layers of n type and p type, and a ()-oriented 4H-SiC n+-type substrate. The CL spectra, recorded at various temperatures and at various excitation conditions, show strong differences between the polytypes, indicating a better homogeneous distribution of radiative centres inside the 6H polytype than in the 4H one, and also between the different orientations. For the ()-oriented 4H sample, luminescence features decrease when the excitation intensity increases, probably due to a more significant indirect transition band. The CL spectra also vary for the same sample, due to the impurity and the microscopic defect density variations. Comparisons between two local spectra taken in two distinct areas of the ()-oriented 4H sample, and with images obtained by x-ray topography in the same areas, allow us to establish that some structural defects are involved in luminescence centres. A deep centre involved in green luminescence (at 1.80?eV) is found to be associated with basal plane dislocations with the Burgers vector .

Influence of metal trapping on the shape of cavities induced by high energy He+ implantation

In He implantation induced cavities highly contaminated with metals (Au, Ni, Pt) we found that, when no three-dimensional structure is observed, the shape of the cavities can be strongly modified depending on the nature of the metal and on its trapped quantity. The equilibrium shape of cavities is the Wulff shape associated with the minimum surface energy which can be determined using the code WULFFMAN. On the basis of these computations the effect of a metal chemisorption may be accounted for. At very low coverage (far below 1%) there is no effect to be expected. At coverages between 1% and 10%, independent of the nature of the metal, a reduction of the specific surface energy of the vicinal surfaces may produce spherical cavities. Eventually for coverages close to one monolayer, the specific surface energy of the concerned metal will drive the cavities toward spherical or highly facetted shapes depending on whether the specific energy of the metal is smaller or higher than the vicinal one of silicon.

Phase characterization in Si3N4-SiC particulate composites performed by EELS in a 1 MV microscope

Abstract The purpose of this work was to determine the origin of the influence of SiC on the Si3N4 grain growth in Si3N4-SiC particulate composites. Materials containing either 17 wt% or 34 wt% of SiC were analysed by electron energy-loss spectroscopy (EELS) in a 1 MV microscope. The typical EELS spectra of the different constituents were obtained. They included plasmon distribution and inner-shell excitation edges. The distribution of SiC grains in the composite was determined. A qualitative analysis of the intergranular phase was performed which demonstrates that dissolution-precipitation in the liquid oxide phase of both SiC and Si3N4 occurs during the sintering and thus influences the Si3N4 grain growth.

Analysis by Sims and by Eels-Edx in a Stem of Sic Fibers Reinforced Composites

A series of Nicalon SiC fibers (202) coated by CVD with C and SiC were analysed by Secondary Ion Mass Spectrometry (SIMS). Results (i) give the composition of the material, (ii) show its heterogeneity of composition, and (iii) demonstrate the limit of application of the method for the fibers analyses. SIMS and Electron Energy Loss Spectroscopy (EELS) analyses of one coated fiber segment were done. When elements are detected by both techniques, reasonable agreement is observed between the results. SiC - CVD deposits are not uniform: they are rich in carbon close to the fiber and tend towards stoechiometry after a few microns. The coated fibers are rich in oxygen and in free carbon. Analyses of a glass-ceramic matrix/ Nicalon SiC fiber (202) composite were performed using SIMS, EELS and Energy Dispersive X-Ray Spectroscopy (EDX).

Roles of Impurities and Implantation Depth on He + - Cavity Shape in Silicon

Silicon samples were implanted with He + ions at energies varying from 10keV to 1.55MeV using doses ranging from 1.45×10 16 cm -2 to 5×10 16 cm -2 to obtain similar He concentration at each projection range (R p ). In few samples, gold, platinum, nickel or silver was introduced prior to He + implantation by diffusion at temperatures ranging from 870°C to 1050°C. All samples were annealed in the 400°C–1050°C temperature range to determine the equilibrium stage of the growth of the cavity. The cavity characteristics (distribution, shape and size) were studied by cross section transmission electron microscopy (XTEM). Their morphology demonstrates the validity of the chemisorption hypothesis when they grow in silicon intentionally contaminated by metal. A consequence of the surface proximity on the cavity characteristics was verified and allows stepping forward two regimes of cavity growth: one, very fast, taking place in a He-free environment and another one, slower, occurring in a He-rich atmosphere.