“…The lack of size quantization effect in type 2 structure (absence of the second peak in the temperature dependence of conductivity) may be due to the accumulation of strains during the growth of successive Ge layers, which leads to an increase in the size of the quantum dots [11], and/or non-uniform strain relaxation, resulting in a large number of defects [12]. Introduction of thick Si spacer layers in type 3 structure should significantly reduce these factors, which leads to the appearance of the size quantization in Ge quantum dots and, thus, the appearance of the second peak in the temperature dependence of conductivity.…”