Dislocation-free undoped semi-insulating GaAs epilayers prepared by chloride chemical vapor deposition and successive wafer annealing

Do Solids Flow?

“…They cost infinite energy 2 and, hence, they are absent in three-dimensional crystals at thermal equilibrium. Although equilibrium crystals can be prepared [5,6], typical growth procedures lead to imperfect crystals characterized by a dislocation density that ranges from 10 6 − 10 10 cm −2 . When a shear stress σ is applied, dislocations move with a velocity proportional to the stress and lead to what is called plastic flow [7].…”

“…In the following we investigate in more detail the flow process and endeavor to obtain some predictions for the flow curve of a "solid". For not too small shear stresses, there is a finite density of critical nuclei 6 and one has to take into account their growth and their continuous deformation due to a constant shear rate. Forgetting the continuous deformation for the time being, one finds that the growth is a two-stage process: critical nuclei first expand driven by a free-energy gain, until they start to overlap.…”

“…The pre-requisite to discover the effect predicted in this work is therefore to prepare perfect crystals. This is not an easy procedure but it can be done [5,6]. Colloids are other interesting systems to test our results.…”