Misfit Dislocations In Epitaxial Layers Research Articles

Nondestructive evaluation of misfit dislocation densities in ZnSe∕GaAs heterostructures by x-ray diffuse scattering

Estimating the low densities of misfit dislocations in epitaxial layers in the early stages of relaxation is difficult, requiring a very sensitive method. The characteristic patterns of diffuse x-ray scattering are therefore utilized to quantify the linear density of misfit dislocations. This is demonstrated for ZnSe∕GaAs(001) heterostructures with ZnSe layer thickness slightly above the critical thickness. The densities that resulted from calculated patterns of x-ray scattering perpendicular to the diffraction vector are found to be in good agreement with the results of cathodoluminescence and transmission electron microscopy. Moreover, the diffuse x-ray scattering is used to quantitatively study the thermally induced increase in the linear densities of misfit dislocations. Samples are annealed at various temperatures for increasing periods successively and are analyzed between the annealing steps by high-resolution x-ray diffraction. The density of dislocations is found to saturate for longer annealing periods. The saturation value and the rate of increase of the dislocation density depend both on the annealing temperature and on the crystallographic direction.

Interaction characteristics of dislocations in strained epitaxial layers

In connection with nucleation and multiplication processes of misfit dislocations in epitaxial layers, elastic interactions of some configurations of dislocation surface half-loops and angular dislocations are investigated. By using the programme code produced by Gosling and Willis [J. Mech. Phys. Solid 42, 1199 (1994)], which calculates the image stresses of a straight dislocation half-line in a half-space and enables one to construct the stress field of any configuration of dislocation loops, the interaction energy of two surface half-loops is obtained. With the change of the relative positions of the two half-loops, the sign of the interaction energy varies from minus to plus, in accordance with which the interaction force between the two half-loops varies from an attractive force to a repulsive one. The interaction forces exerted on threading segments are also estimated for two angular dislocations, and their effects on the Matthews and Blakeslee equilibrium are discussed.

Diffuse x-ray scattering from misfit dislocations in SiGe epitaxial layers with graded Ge content

A theory has been developed describing x-ray diffuse scattering from misfit dislocations in epitaxial layers. This approach has been used for explaining the origins of diffuse x-ray scattering from SiGe layers with linearly graded Ge content. The distribution of the diffusely scattered intensity in reciprocal plane measured by triple-axis x-ray diffractometry has been compared with theoretical predictions and a good agreement has been achieved. It is demonstrated that the main part of the diffusely scattered intensity originates from random strains caused by misfit dislocations at the substrate–epilayer interface or in the relaxed part of the compositionally graded layers. The contribution of the threading dislocation segments to the diffuse scattering is rather small.

A Multiplication Mechanism for Misfit Dislocations

ABSTRACTA new mechanism which describes how misfit dislocations in epitaxial layers multiply is presented. This work demonstrates how a single threading dislocation can give rise to an array of dislocation sources, where each source generates a single dislocation loop perpendicular to the primary misfit dislocation. As a threading dislocation with pure screw character glides through an epilayer, certain processes occur which lead to the production of a single dislocation half-loop, and the regeneration of the original threading dislocation. The regenerated threading dislocation continues to propagate on its primary glide plane, which allows the process to repeat itself at some later time. The result of this sequential process is an array of half-loops perpendicular to the primary misfit dislocation. The shape and symmetry of the arrays also contains information regarding how the mechanism operates. The proposed mechanism is related to misfit dislocation arrays in a single Si0.87Ge0.13 layer on Si(001).