Acceptor impurity concentration

Similarly, one can derive an equation for a p-type semiconductor, where the distance between the Fermi energy level and the valence band is a logarithmic function of acceptor impurity concentration. As the acceptor impurity increases so too does the hole concentration in valence band, with the Fermi level moving closer to the valence band. 

Pa < p0z < 105Pa (BD) The oxygen vacancy concentration now determined by the acceptor impurity concentration [A ], is little affected by changes in Po2 and remains sensibly constant. It follows from Eq. (2.49) that... 

Suppose now that the introduction of an acceptor impurity (increase of ev and es ) brings us from the point A to the point C (Fig. 9). This involves an increase in K, as seen from Fig. 9. This is in agreement with the results obtained by the same authors (41), who observed an increase in the photocatalytic effect on silica gel when acceptor impurities were added to the catalyst, and also with the data of Lunsford and Leland (42) who found that the effect was enhanced on MgO with increasing concentration of V-centers (acceptors). 

This chapter is devoted to the energetics and kinetics of the incorporation of hydrogen into the simplest and most studied of its possible hosts, crystalline silicon of high perfection containing known concentrations of shallow donor or acceptor impurities. It undertakes to review what has been learned from experiments about the phenomenological parameters... 

By varying the impurity concentration in the semiconductor, one may regulate not only the activity of the catalyst but its selectivity as well. Indeed, if the reaction proceeds along two parallel paths, one of which is of the acceptor type and the other of the donor type, then upon the monotonic displacement of the Fermi level (i.e., upon the monotonic change of Z) the reaction will be accelerated on one path and retarded on the other, as appears, e.g., from a comparison of Figs. 19a and 19b. Doping of the crystal may accelerate the reaction on one path and retard it on the other. 

We have seen that, at finite temperature, there will always be free carriers in a semiconductor, either by virtue of intrinsic excitation or as a result of a donor or acceptor impurity. From the electrochemical viewpoint, the most important result of this carrier concentration is that the material exhibits a finite conductivity. This conductivity is given by... 

It is essential that the silicon be intrinsic (/). It must neither be -type, containing free electrons from donor impurities, nor p-type, containing free holes from acceptor impurities in either type, the free charge carriers, at their usual concentrations, would overwhelm the few carriers produced by x-rays. Production of a reasonably large intrinsic crystal, which is not easy, requires two operations ... 

Thus, the result of optimization is a number, namely the value of the optimal concentration of donor or acceptor impurities. Naturally, the theory cannot indicate the exact figure of doping impurity concentration. Therefore the optimal concentration is experimentally determined by way of creating materials with different impurity concentrations and determination of their Z. 

The dependence of partial surface concentrations of 02 and C2H4 on variations in (j> of the catalyst seems to explain the unsteady nature of reaction kinetics. It will be expected, moreover, that addition of acceptor impurities will raise the reaction order for oxygen and decrease it for ethylene. The zero reaction order with respect to oxygen in the formation of C2H40 and C02, as found by Temkin et al., may apparently be explained as follows. 

---