Structural stability and scanning tunneling microscopy images of strained Ge films on Si(001)

We investigate energetics and scanning tunneling microscopy (STM) images of several Ge films on Si(001) substrates using a first-principles total-energy calculation within the density-functional theory. We calculate the film energies of various Ge films with dimer-vacancy lines (DVL) and 90 ^â̂̃ dislocation cores (DC) deposited on Si(001) substrate as a function of Ge-layer thickness. Our energetics calculation suggests that 90^â̂̃ DC structure becomes stable when sufficiently thick Ge overlayers are deposited on Si(001) substrate. We also calculate the STM images of p(2×2), 2×8 DVL, and 90 ^â̂̃ DC structures, and we find that STM images of their surface structures are distinguishable from one another.