Yasuhiko Ishikawa

Reduction of threading dislocations by image force in Ge selective epilayers on Si

Because of the 4% lattice mismatch between Ge and Si, threading dislocations (TDs) are generated in Ge epilayers on Si, deteriorating the performance of Ge devices on Si platform. We recently modeled the reduction of TD density in heteroepitaxial coalesced layers in terms of the bending of TDs induced by image forces at non-planar selective epitaxial growth (SEG) surfaces before the coalescence. The reduction of TD density was quantitatively verified for Ge layers on (001) Si with line-and-space SiO2 masks. In the present paper, detailed theoretical calculation and experimental results are presented. Numerical calculation shows that the image force is large enough to bend/move dislocations considering the Peierls stress or the mobility of TDs in Ge. Transmission electron microscope observations show that the TD bending is certainly induced. The TD density is lower above the SiO2 masks, as confirmed by the etch pit method. Such spatial distribution is well explained by the image-force-induced dislocation bending.