Semiconductors with isoelectronic impurity clusters are actively studied now as promising materials for device applications. The heterogeneity of clusters in shape, size and composition is a serious obstacle to their use. The formation conditions of identical impurity clusters in Ge:(C, Pb) is presented. Ge:(C, Pb) is Ge-rich CxPbyGe1-x-y alloy. The stiffness coefficients, bond stretching and bond bending elastic constants of Pb with the diamond structure are estimated. The self-assembling conditions of 4C10Pb and 1C4Pb clusters in Ge:(C, Pb) obtained by minimizing the free energy are calculated from 0 degrees C to 800 degrees C and with impurity contents in the dilute and ultra-dilute limits. The formation of 4C10Pb clusters is more favorable than that of 1C4Pb clusters. The majority of carbon atoms should be in 4C10Pb clusters with impurity contents x = 6 x 10(-4), y = 3 x 10(-3) and x = 4 x 10(-4), y = 2 x 10(-3) up to 700 degrees C. The most Pb atoms have to be in 4C10Pb clusters in alloys with x = y = 3 x 10(-3) and x = y = 1 x 10(-3) up to 700 degrees C. Accordingly, a high temperature treatmentmay be used for self-assembling stimulation if 4C10Pb clusters were not formed during a growth process. The conditions demonstrate that Ge:(C, Pb) are promising materials to obtain arrays of the identical isoelectronic impurity clusters with the desired density. (C) 2017 Elsevier B.V. All rights reserved.