MACROSEGREGATION DURING BRIDGMAN GROWTH OF GE1-XSIX MIXED-CRYSTALS

We investigated the Bridgman growth of non-dilute Ge1-xSix mixed cryst als and report on four samples of different composition. They are char acterized by metallography and composition analysis. The macroscopic a xial concentration profile is close to that of a completely mixed melt . The hydrodynamical origin of this strong stirring is discussed. Fluc tuations of growth rate and/or composition result in strong striation patterns. The spacing bf the striae is found to be similar for all mel t volumes, compositions and thermal environments used in our experimen ts, The crystal quality is generally poor. All samples show a grain st ructure. If the seed is of higher Si content than the first part of th e grown crystal, formation of grains is considerably reduced. A model for understanding this finding is proposed.