CONTROLLING THREADING DISLOCATION DENSITIES IN GE ON SI USING GRADED SIGE LAYERS AND CHEMICAL-MECHANICAL POLISHING

A method of controlling threading dislocation densities in Ge on Si in volving graded SiGe layers and chemical-mechanical polishing (CMP) is presented. This method has allowed us to grow a relaxed graded buffer to 100% Ge without the increase in threading dislocation density norma lly observed in thick graded structures. This sample has been characte rized by transmission electron microscopy, etch-pit density, atomic fo rce microscopy, Nomarski optical microscopy, and triple-axis x-ray dif fraction. Compared to other relaxed graded buffers in which CMP was no t implemented, this sample exhibits improvements in threading dislocat ion density and surface roughness. We have also made process modificat ions in order to eliminate particles due to gas-phase nucleation and c racks due to thermal mismatch strain. We have achieved relaxed Ge on S i with a threading dislocation density of 2.1 X 10(6) cm(-2), and we e xpect that further process refinements will lead to lower threading di slocation densities on the order of bulk Ge substrates. (C) 1998 Ameri can Institute of Physics. [S0003-6951(98)01214-5].