Transmission electron microscopy in situ investigation of dislocation mobility in semiconductors

TEM in situ straining experiments provide a unique way to investigate in real time the behaviour of individual dislocations under applied stress. The results obtained on a variety of semiconductors are presented: numerous dislocation sources are observed which makes it possible to measure the dislocation velocity as a function of different physical parameters (local shear stress, temperature, dislocation character, length of the moving dislocation,...). The experimental results are consistent with a dislocation glide governed by the Peierls mechanism, even for II-VI compounds which have a significant degree of ionic character. For compounds, a linear dependence of the dislocation velocity on the length of the moving segment is noticed, whereas for elemental semiconductors a transition between a length-dependent and a length-independent velocity regime is observed. Analysed in the framework of the kink diffusion model (Hirth and Lothe theory), these results allow an estimation of the kink formation and migration energies. For a variety of semiconductors, the dislocation behaviour is sensitive to electronic excitations. A strong increase of dislocation mobility with increasing electron beam intensity is observed (radiation-enhanced dislocation glide). It is attributed to a lowering of the lattice friction, due to non-radiative recombinations of electronic carriers at dislocation sites.