Solubility: The solubility of a dopant in the substrate also plays a key role. Even if the diffusivity is large, if the solubility is small, then it will take a long time to achieve a particular level of doping. This is because the total quantity diffused depends on the concentration gradient and the diffusivity. The concentration gradient depends on the solubility limit.

Typically, the solubility of dopant is much more than the doping level required. The solubility is a function of temperature and for most dopants, it varies between 10¹⁹ to 10²¹ atoms-cm^-3 in the temperature range of  400 -1000 ˚C. For impurities such as Cu, Fe or Au, the solubility is in the range of 10¹⁵ to 10¹⁸ atoms-cm^-3 in the same temperature range.

At 1000 ˚C, the diffusivity of As in Si is in the range of 10^-15 cm²/s, B in Si is in the range of 10^-14 cm²/s and P in Si is in the range of 5 ×10^-15 cm²/s. On the other hand, the diffusivities of some of the contaminants are much higher. For example, in Si at 500 – 1000 ˚C range, the diffusivity of Cu, Fe  and Au are in the range of 10^-2 to 10^-7 cm²/s.