Defects generated by misfit strain in SiGe/Si(001)

The structure of misfit dislocations in a ${\mathrm{Si}}_{0.67}$${\mathrm{Ge}}_{0.33}$/Si(001) strained-layer superlattice by transmission electron microscopy (TEM) has been analyzed. An orthogonal set of misfit dislocations, using plan-view TEM specimens, was observed at the strained-layer interfaces relaxing the strain in the structure. Conventional g⋅b diffraction contrast experiments displayed 60°-type misfit dislocations with a/2 〈100〉 {111} slip system. To observe the propagation and generation of misfit dislocations in the superlattice, a number of annealing experiments were carried out in a vacuum furnace at temperatures between 550 and 1050 °C at a pressure of 1×${10}^{\mathrm{-}6}$ Torr for 5 min. The experimental study was performed in the microscope taking micrographs before and after each annealing process. Consequently, two orthogonal sets of misfit dislocations were generated in the superlattice at two different temperatures (760 and 940 °C). It was ascertained that the first set of dislocations is generated by the threading dislocations and the second set is produced by the structure. An interstitial type of dislocation loop was attained for the dislocation generation mechanism at high temperatures.