where q0 and T0 denote material parameters. Here kBT0 ¼ 1:5
a3NðEÞ,
where N(E) is the density of states at the Fermi level and a denotes
the rate of fall-off of the envelope of the electron wave function. The
curve plotted for ln (R/R400) versus (1/T)1/4 shown in Fig. 8a gives a
straight line. From this the value of T0 has been obtained for pure
and Sn–ZnO films. It has been found that the values of T0 decreased
with the increase in Sn content (see Fig. 8b). This suggests that the
density of states increases with the increase in Sn concentration.