Atomic structures and energetics of 90° dislocation cores in Ge films on Si(001)

We report on atomic structures and energetics of 90 degrees dislocation cores in Ge films on Si(001) substrates on the basis of the first-principles total-energy calculations. The dislocation core structure consisting of a row of pairs of five- and seven-membered Ge rings is proposed and found to be stable with increasing Ge overlayers. The scanning tunneling microscopy images of the 90 degrees dislocation core structure are calculated and show the possibility to observe the proposed core structure.