Papers by Keyword: Dislocation Annihilation

Abstract: In this paper the effect of lattice friction stress on the process of dislocations annihilation is considered using dislocation dynamics method. It is shown that if dislocations of the opposite sign are located in the area where their own tension is greater than the friction stress, they annihilate. Consideration of this fact allows to connect the microscopic processes of annihilation with evolution of dislocation density in the sample under small external stresses and unloading. The area in which annihilation occurs is calculated to be proportional to the square of the friction stress/shear modulus ratio.It is also shown that the parameter responsible for the rate of dislocation annihilation depends on the cube of the ratio of the friction stress to the shear modulus, because it is inversely proportional to the number of annihilating dislocations and the time in which a dislocation pair annihilates.

Abstract: Epitaxial group-III nitride films, although in single crystalline form, contain still a large number of threading dislocations. These set limits to performance and lifetime of devices, notably to high power structures like lasers. The strategy in material development was and will be (at least until lattice-matched substrates become available) to reduce the dislocation densities. The present contribution elaborates on possible dislocation origination mechanisms that determine the population of dislocations in the epitaxial layers. These mechanisms can be controlled to a certain degree by proper deposition procedures. The achieved dislocation populations then determine the processes that can reduce the dislocation densities during growth of the epitaxial layers. The mutual annihilation of threading dislocations is rather efficient although affected by the glide properties of the growing epitaxial crystal and the thermal stresses during the cooling down after growth.