The Hall values of mobility and electron concentration are also plotted in Fig. 5 for samples B and C. For B samples, varies only by a factor of 3.3, while varies by a factor of 3.0, so both factors contribute nearly equally to the observed 10-fold variation in resistivity. Since the mobility values for B and C samples are about the same, their difference in resistivity value is due mainly to their different electron concentrations. The electron and actual fluorine concentrations in sample C20 are and , a difference of only 14%, which is comparable to the level of uncertainty for [F] values from SIMS. A similar situation holds for sample B10. This suggests that a substantial portion of F dopant ions in SPEED-grown films can be electrically active. On the other hand, with decreasing [F], the electron concentration does not drop proportionally. For the lowest doped sample, by a factor of , which suggests an additional source of free carriers, possibly oxygen-vacancy double-donors. The resistivity of the undoped film before ion-implantation was determined by 4-pt probe to be , which is a factor 20 to 750 higher than for the F-doped samples shown in Fig. 5. That means that the doping process during SPEED growth is responsible for all of the additional charge carriers, even if they cannot all be accounted for by the concentration of F. Interestingly, the implanted standard prepared for SIMS had a resistivity of , i.e., higher than that of the undoped film before implantation. This suggests that implant damage substantially worsens the electron mobility and that the implanted F ions are not all electrically active. Thus, ion implantation is a poor approach to preparing FTO, unless a suitable annealing process can be developed to heal the damage and activate the dopants. In any case, SPEED has the practical advantage over implantation of being a low-cost, large-area fabrication process.