Physical origin of trench formation in Ge∕Si(100) islands

Monte Carlo simulations of stress buildup and relief shed light onto the physical origin of trench formation in Ge∕Si(100) islands. By monitoring the stress evolution as the island grows layer by layer, we find that a trench is most likely being formed halfway during growth. The primary driving force for this phenomenon is the reduction of the concentrated stress below the edges of the island, but not the need to provide Si into it, as is widely believed. However, once the trench is formed, subsequent intermixing through it is enhanced, and nearly compensates for the stress in the island.