Question

Fig. 6.11 illustrates logarithmic electric conductance as a function of reciprocal temperature (T in kK units) for some n-type semiconductor. Using this plot, find the width of the forbidden band of the semiconductor and the activation energy of donor levels.

Answer 1

At high temperatures (small values of T-1) most of the conductivity is intrinsic i.e. it is due to the transition of electrons from the upper levels of the valance band into the lower levels of conduction vands**.**

For this, we can apply approximately the formula

At low temperatures (high values of 1/T) the conductance is mostly due to impurities. If E0 is the ionization energy of donor levels then we can write the approximate formula (valid at low temperature)

The slope must be calculated at low temperatures. Evaluation gives the slope