Misfit accommodation in epitaxial Ge films on Si

Abstract

Electron microscopy is well suited for the study of the initial stages of misfit dislocation nucleation and of dislocation reactions. High-resolution Z-contrast imaging has the added advantages of producing intuitively interpretable images with chemical sensitivity. This technique has been used to study film formation and misfit accommodation in epitaxial Ge films grown on Si. The epitaxial Ge films studied herein were produced by steam oxidation of Ge-implanted (001) Si. The implanted Ge is rejected by the growing SiO2 layer and has no time to diffuse into the Si. The partitioned Ge forms a distinct strained epitaxial layer on Si. With this growth process the Ge films are constrained to grow layer-by-layer instead of the normally observed island mode. The growth morphology in turn governs the interfacial misfit dislocation nucleation, location, and character.Figure 1 shows a cross-section view of a dislocation-free 5-nm thick Ge film on (001)Si produced by the oxidation of a Ge (2×l016 ions/cm2) implanted Si wafer. This is three to six times thicker than the observed critical thickness for Ge films grown on Si by more conventional growth processes. Ge normally grows as islands on Si and, after the equivalent of six monolayers of Ge is deposited, dislocations are introduced at the island parameters to relieve the misfit strains.