FACET FORMATION IN STRAINED SI1-XGEX FILMS

The surface morphology of epitaxial (001) Si1-xGex films, subject to biaxial strain, is studied by atomic force microscopy (AFM). Distinct facets are observed, oriented on {105}, {311}, and {518} crystal faces. The tiled arrangement of facets resembles a mosaic. We find that the growth sequence begins with the shallow {105} facets, followed by the appearance of steeper facets. After strain relaxation, the morphology coarsens and facets become less distinct. The existence of discrete facets produces a kinetic barrier to strain-induced roughening; and we show that increasing this barrier (by growing at reduced strain or reduced temperature) leads to a flatter surface morphology.