The relationship between activation parameters and dislocation glide in 4H-SiC single crystals

4H-SiC single crystals were deformed by compression in the temperature rang e 550 to 1300 degreesC and a strain rate range of 3.1 x 10(-5) to 6.5 x 10( -4) s(-1) to determine the critical resolved shear stress for slip on the ( 2(11) over bar 0)(0001) primary slip system. Two different methods to deter mine the activation parameters for dislocation glide were examined. In the first method, where the activation enthalpy for dislocation glide DeltaH(g) is assumed to be a function of the applied stress tau, DeltaH(g) drops fro m similar to7.4 eV at tau approximate to 8 MPa to similar to2.8 eV at tau a pproximate to 235 MPa. In the second method, where the activation enthalpy for dislocation glide, Q, is assumed to be stress-independent, the values d etermined at strain rates of less. than 6.3 x 10(-5) s(-1) were Q approxima te to (2.1 +/- 0.7) eV at low temperatures (T < 1100<degrees>C) and Q appro ximate to (4.5 +/- 1.2) eV at high temperatures (T > 1100 degreesC). Transm ission electron microscopy investigations of the deformed samples show that very different configurations of dislocations are activated under the acti on of the applied stress. At 1300 degreesC, the dislocations were all perfe ct, albeit dissociated into leading/trailing partials separated by a ribbon of stacking fault, while at 700 degreesC only single leading partials, eac h dragging a stacking fault and without their corresponding trailing partia ls, were observed.