Dislocation interaction of layers in the Ge/Ge-seed/GexSi1−x/Si(0 0 1) (x ∼ 0.3–0.5) system: Trapping of misfit dislocations on the Ge-seed/GeSi interface

Abstract

High-resolution electron microscopy has been applied to study the dislocation redistribution between Ge and GeSi layers at the atomic scale. Ge0.3Si0.7 (30nm in thickness) and Ge0.5Si0.5 (10nm) buffer layers buried between the Si(001) substrate and the plastically relaxed Ge layer 0.5μm thick remain in a metastable (stressed) state during the growth of Ge/Ge-seed/GexSi1−x/Si(001) (x∼0.3–0.5) heterostructures, though the buffer layer thickness is several times greater than the critical value for insertion of misfit dislocations (MDs). An ordered grid of edge MDs is observed only on the Ge/GeSi interface; the mean distance between the MDs is ∼10nm (which is close to the equilibrium value for the non-stressed Ge/Si system). After 30min of annealing at 700°С, the Ge0.3Si0.7 buffer layer still remains in a metastable state, and the edge MDs are located only on the Ge/GeSi interface with the same dislocation spacing of ∼10nm. At the same time, approximately one-half of MDs in the structure with the Ge0.5Si0.5 buffer layer passes through the Ge/GeSi interface to the GeSi/Si(001) interface, and the buffer layer plastically relaxes by almost 100%. An assumption is put forward that there exists a barrier for the MD transition from the Ge layer to the GeSi layer, which results in MD trapping on this interface. The magnitude of this barrier depends on the difference in the compositions of the main Ge (x=1) film and the GexSi1−x buffer layer, and increases with increasing this difference.