A method of controlling threading dislocation densities was presented, for Ge on Si, which involved graded SiGe layers and chemical-mechanical polishing. It permitted the growth of a relaxed graded buffer to 100% Ge without the increase in threading dislocation density that was normally observed in thick graded structures. The specimen was characterized by using transmission electron microscopy, etch-pit techniques, atomic force microscopy, Nomarski optical microscopy, and triple-axis X-ray diffraction. When compared with other relaxed graded buffers in which chemical-mechanical polishing was not used, the present sample exhibited improvements in threading dislocation density and surface roughness. Relaxed Ge layers on Si were obtained, with a threading dislocation density of 2.1 x 106/cm2.

M.T.Currie, S.B.Samavedam, T.A.Langdo, C.W.Leitz, E.A.Fitzgerald: Applied Physics Letters, 1998, 72[14], 1718-20