Islands formation conditions in silicon-germanium alloys grown by MBE

Islands formation on Si1-xGex epitaxial layers has been investigated by electron microscopy techniques in order to study the correlation between the mechanisms of islands growth and the deposition parameters such as the substrate temperature (T-s) and Ge content (x). In this respect, two sets of samples were prepared: the first set was deposited keeping T-s constant at 600 degrees C and varying x from 0.44 to 0.89, whereas the second set was deposited at a constant x = 0.68 value varying T-s in the range 400-700 degrees C. Results evidenced that at high values of strain the formation of large and thick islands is energetically favoured and that, at a constant strain value, their nucleation takes place above a critical substrate temperature.