J. L. Demenet

On transition temperatures in the plasticity and fracture of semiconductors

Abstract Recent experiments on deformation of semiconductors show an abrupt change in the variation in the critical resolved shear stress τY with temperature T. This implies a change in the deformation mechanism at a critical temperature T c. In the cases examined so far in our laboratories (Case Western Reserve University and Poitiers) and elsewhere, this critical temperature appears to coincide approximately with the brittle-to-ductile transition temperature T BDT. In this paper, new deformation experiments performed on the wide-bandgap semiconductor 4H-SiC over a range of temperatures at two strain rates are described together with a transmission electron microscopy characterization of induced dislocations below and above T c. Based on these, and results recently reported on a few III–V compound semiconductors, a new model for the deformation of tetrahedrally coordinated materials at low and high temperatures is proposed, and the relation of the transition in deformation mode to the transition in fracture mode (brittle to ductile) is discussed.

Microstructures of 4H–SiC single crystals deformed under very high stresses

The microstructure of 4H–SiC single crystals deformed under very high stresses and at low temperature (T ≤ 350°C) have been analysed by transmission electron microscopy. Depending on deformation conditions, large stacking faults, weakly dissociated perfect dislocations and possibly undissociated perfect dislocations have been observed. From these results, it appears that the nucleation of partial dislocations, which is a limiting process in deformation of 4H–SiC below ~1000°C, can be helped by very high stress. Consequently, it is not excluded that a deformation mechanism by undissociated perfect dislocations can take place under very high stress, as observed in Si and GaAs.

TEM study of defects generated in 4H-SiC by microindentations on the prismatic plane

The deformation microstructure of single crystals of 4H-SiC resulting from microindentations on a prismatic surface was investigated by TEM. Indentations were performed at 400 and 675°C, i.e. below the brittle to ductile transition temperature of 4H-SiC (temperature close to 1100°C). TEM analysis reveals dissociated dislocations as well as extended stacking faults in the basal plane. In addition, perfect edge dislocations are observed on prismatic planes. From the observations, it is assumed that perfect dislocations are nucleated in the prismatic plane and cross-slip on the basal one where they dissociate.

Characterization of room-temperature plastic deformation of ß-Si3N4 by atomic force microscopy and transmission electron microscopy

Dislocation microstructures induced by room-temperature microhardness tests have been investigated in silicon nitride. Surface analysis of the residual indent by atomic force microscopy reveals intragranular slip bands and demonstrates that room-temperature plastic deformation involves dislocation motion as well as cross-slip events. Cross-slip events have been found to occur between {1010} prismatic planes. Transmission electron microscopy shows that dislocations have a Burgers vector b = [0001] and are located along the screw direction. Based on these observations, specific dislocation core configurations are discussed.

Plasticity of InSb at Low Temperature: Analysis of Microstructures by Transmission Electron Microscopy

This paper considers the plasticity of InSn under high stress, at low temperatures. The studies cover the plasticity of InSh in the temperature range between 20 and 200°C and under stress which is applied by superimposing uniaxial pressure on a confining hydrostatic pressure. The analysis of the deformed substructures by transmission electron microscopy revealed the existence of different deformation mechanisms at different temperatures, and consequently. stress regimes At temperatures T ≥ 50°C the dominant deformation mechanism is the glide of perfect dislocations, while at room temperature the deformation can be attributed to partial dislocations. At lower temperatures. screw dislocalions become dominant, a fact that demonstrates the small mobility of these dislocations. Extended stacking faults introduced by the dissociation of β-type segments demonstrate the higher mobility of the 90 β partial dislocations conspired to the mobility of the 30 β ones. In contrast, the absence or extended dissociation for the 60 α-type dislocations suggests that the 90 α and the 30 α partial dislocations have the sortie mobility An additional interesting issue arises from the observations showing a small difference in mobility between the 30 α and the 30 β partial dislocations The significance of these observations is discussed and the results are correlated to similar observations in other III-V compounds.

A Revisitation of Some Problems of Dislocations in Silicon

Dislocation microstructures obtained following plastic deformation close to the Brittle to Ductile Transition temperature have been investigated using multiscale imaging techniques. TEM investigations show a multiplicity in the dislocation core configurations which can appear as dissociated of as perfect segments. The evidence, after etching, of trails of point defect behind dislocations is also characteristic of these deformation conditions. These observations are discussed in the light of the possible core structures of dislocation proposed in silicon.

Deformation-induced dislocations in 15R-SiC grown by sublimation

Single-crystal 15R-SiC boules have been successfully grown by sublimation. The Vickers hardness of a Si-terminated (0001) face has been measured in the temperature range 25-1300C. As expected, the hardness decreases with increasing temperature from about 30GPa at room temperature to about 10GPa at 1300C. The fracture toughness is estimated to be about 1.0MPam 1/2 at room temperature. Transmission electron microscopy investigation of the dislocations introduced by indentation at 900 and 1300C shows that they are activated predominantly on the basal plane. Most of them consist of a single leading partial without the corresponding trailing partial.

Effect of electronic doping on the plasticity of homoepitaxial 4H-SiC single crystals

Instrumented micro-indentations have been performed at room temperature on 4H-SiC homoepitaxial single crystals with different doping. For these experiments, it appears that the pop-in event occurs at the same level of load for intrinsic and n-type SiC and at a higher load level for p-type. Correlation of the pop-in event with dislocation nucleation indicates that doping acts on dislocation nucleation and that p-type doping plays a hardening role on the plastic behaviour of 4H-SiC. This result is confirmed by the conventional measurement of imprint size using scanning electron microscopy.