A Note on the Theory of Semiconductors

One obtains two different theories of semiconductors, depending on whether the free energy due to the spin of electrons in donor (or acceptor) centres is taken into account (approach A) or not (approach B) it is shown (i) that the former approach can be carried through for a degenerate semiconductor, (ii) that it applies formally to the case when the interaction between impurity centres and conduction electrons is taken into account, provided one of the symbols is reinterpreted, and (iii) that it is to be preferred. Approach B has, however, been used almost universally It is shown that it corresponds to the unlikely situation in which fifty per cent of the electrons from each impurity level come from paired states, and the remaining fifty per cent from unpaired states having the same activation energy.