A TEM IN-SITU INVESTIGATION OF DISLOCATION MOBILITY IN THE II-VI SEMICONDUCTOR COMPOUND ZNS - A QUANTITATIVE STUDY OF THE CATHODOPLASTIC EFFECT

The cathodoplastic effect has been studied in ZnS by in situ transmiss ion electron microscopy (TEM) deformation experiments in the temperatu re (T) range 290-470 K and for electron beam intensities (I) varying f rom 35 to 5600 A m-2. The dislocation glide governed by the Peierls me chanism is greatly enhanced by increasing I. The velocity per unit len gth (P) of screw and both types of 60-degrees dislocations varies line arly with I below a critical intensity I(S); then, it tends to saturat e. These results are consistent with a radiation-enhanced dislocation glide (REDG) mechanism. Thermal activation energies for dislocation mo tion are estimated to 1-16 +/- 0.10 eV in the absence of electronic ex citation and 0.30 +/- 0.10 eV under electron irradiation. For I < I(S) , screw and both kinds of 60-degrees dislocations (alpha,beta), have s imilar activation energies unlike the other semiconductor compounds. I n the frame of the REDG model, the reduction in activation energy is a ttributed to the energy released upon non-radiative capture of excited carriers at straight dislocation sites.