We investigated the effects of low temperature (LT) Ge buffer layers on the two-step Ge growth by varying the thickness of buffer layers. Whereas the two-step Ge layers using thin (<40 nm) Ge buffer layers were roughened due to the formation of SiGe alloy, pure and flat Ge layers were grown by using thick (>50 nm) LT Ge buffer layers. The lowest threading dislocation density of 1.2 x 10(6) cm(-2) was obtained when 80-nm-thick LT Ge buffer layer was used. We concluded that the minimum thickness of buffer layer was required to grow uniform two-step Ge layers on Si and its quality was subject to the thickness of buffer layer. (C) 2010 Elsevier B.V. All rights reserved.