Isolation and Control of Voids and Void-hillocks during Molecular Beam Epitaxial Growth of HgCdTe

Void defects were demonstrated to form away from the substrate-epifilm interface during the molecular beam epitaxial growth of mercury cadmium telluride on cadmium zinc telluride substrates. These were smaller in size compared to voids which nucleated at the substrate-epifilm interface, which were also observed. Once nucleated, voids usually replicated all the way to the surface even if the flux ratios were modified to prevent additional nucleation of voids. Occasionally, void defects which close before reaching the top surface without leaving any perturbations on the surface, have also been observed. The voids which form away from the substrate-epi interface, nucleate on defects, frequently hillocks, introduced into the film already grown, leading to formation of defect complexes. These voids can be smaller than 1 μm and appear almost indistinguishable from unaccompanied simple voids. However, these void-hillock complexes displayed a nest of dislocations decorating these defects, which become apparent upon dislocation etching, whereas unaccompanied simple voids did not. The nests could extend as much as 25 μm from the individual void-hillock complex. The density of dislocations within the nest exceeded 5 x 10 cm, whereas the dislocation density outside of the nest could decrease to < 2 x 10 cm.