Formation and Stability of 90 Degree Dislocation Cores in Ge Films on Si(001)

The atomic structures and energetics of 90-degree dislocation cores in Ge films on Si(001) substrates are investigated using the first-principles density-functional calculations. To discuss the energetics of 90-degree dislocations, pairs of five- and seven-membered Ge rings are proposed as the core structure of 90-degree dislocation. The proposed core structure is found to be energetically stable with increasing Ge overlayers and we discuss the critical thickness of 90-degree dislocation.