Nature,origin and effect of dislocations in epitaxial semiconductor layers

The paper is concerned with the manner in which dislocations in Group 3–5 compound epitaxial layer structures are generated, propagate and interact with one another. The different types of epitaxial layer and dislocation behaviour are initially reviewed. The examination methods used are based on electron microscopy. The TEM is used in conjunction with plan-view, cross-section, and angle-lap specimens to determine the detailed nature and three-dimensional distribution of the dislocations. The SEM EBIC and CL methods are used with bulk specimens to obtain electrical and luminescent information. In particular, the latter methods give micrograph-type images showing dark spots and lines corresponding to individual dislocations, the contrast arising because of electrical carrier recombination taking place at the dislocations. These methods are used to investigate the dislocation behaviours occurring in a wide range of specimens including homo- and hetero-epitaxial layers, and embracing small, medium and large mismatches. An attempt is made to obtain quantitative data concerning the processes occurring. The work has provided a better understanding in many instances, and sometimes allowed the occurrence of the dislocations to be better controlled. An example is given of the application of the results to the improvement in the quality of a GaAs transmission photocathode device-type structure.