Dopant redistribution: We should note that the solubility of the species also plays an important role in deciding the growth rate. For example the solubility of stream in oxide is much more than the solubility of dry oxygen and hence the growth rate is more in the wet oxidation. There are two reasons why the growth rate is more in wet oxidation. One is that the solubility of stream is more; the second is the oxide formed is porous allowing easy diffusion of the species. Few other parameters also affect the oxidation kinetics. If the silicon is doped then the doping usually increases the oxidation rate, because it will increase the diffusivity. Second the dopant will redistribute silicon and silicon dioxide. This is called segregation. The ratio of dopant in silicon and silicon dioxide is usually not one, hence after oxidation some dopant will either move into the silicon dioxide or it will move away from silicon dioxide and into the silicon. This depends on the nature of the dopant. For example  if boron was originally present, if it was a P-type silicon with boron as the dopant  then it will redistribute itself and will be incorporated in the oxide, it will enhance the diffusion and  the parabolic rate constant will be higher. If phosphorous is present it will not be incorporated into the oxide, and it will not cause significant change in the parabolic rate constant.