Mechanical stability of ultrathin Ge/Si film on SiO2: the effect of Si/SiO2 interface

We perform two-dimensional linear elastic finite element analysis to investigate the mechanical stability of ultrathin Ge/Si film grown on or bonded to SiO2, using imperfect interface elements between Si and SiO2 to model Si/SiO2 interfacial slippage. We demonstrate that the overall composite film is stable when only the tangential slippage is allowed, however, it becomes unstable when normal slippage is allowed: the coherently strained Ge island induces a large local bending of Si layer, and separates the Si layer from the underlying SiO2 forming a void at the Si/SiO2 interface.