To form small and dense Ge dots, an availability of simple bottom-up method by using reaction of Ge and carbon (C) formed on Si(100) at low temperature through post-annealing has been investigated. Ge dots were formed at annealing temperature (TA) above 450 degrees C. Small, dense and relatively uniform dots were formed for Ge = 7.5 MLs and C=0.05-0.1 ML at T-A= 650 degrees C. From the dependence of dot size and density on Ge thickness and C coverage, the effect of C is considered to decrease in bulk free energy of Ge in nucleation process, that is, C led to reduce nucleation barrier height and to decrease critical radius. (C) 2015 Elsevier B.V. All rights reserved.