Heteroepitaxy on compliant substrates: relaxation of misfit stress at low critical film thickness

Abstract

In spite of outstanding experimental success in reducing the density of threading dislocations (TDs) within thin films grown heteroepitaxially on using a compliant substrate instead of a conventional bulk substrate, theories of strain relief on compliant substrates are often based on inadequate theorems like the elastic strain-partitioning and the free-slipping hypothesis. Instead, the present paper modifies the well accepted dislocation model of Matthews by supposing that the misfit dislocations (MDs) relax or dissipate owing to the presence of a weak layer in compliant substrates. This relaxation reduces the drag force on the TDs and therefore the critical film thickness as estimated in a quantitative way. The consequences include less interaction and multiplication of the dislocations, reduced TD density, more homogeneous film structure, and lower final equilibrium strain.