ISLANDS FORMATION CONDITIONS IN SILICON-GERMANIUM ALLOYS GROWN BY MBE

Islands formation on Si1-xGex epitaxial layers has been investigated b y electron microscopy techniques in order to study the correlation bet ween the mechanisms of islands growth and the deposition parameters su ch as the substrate temperature (T-s) and Ge content (x). In this resp ect, two sets of samples were prepared: the first set was deposited ke eping T-s constant at 600 degrees C and varying x from 0.44 to 0.89, w hereas the second set was deposited at a constant x = 0.68 value varyi ng 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 energetic ally favoured and that, at a constant strain value, their nucleation t akes place above a critical substrate temperature.