Analogy of Fermi Level of pH

• The variation of the position of the Fermi level in semiconductors is analogous to the variation of pH in water.

• For a weak acid, as pH in water decreases, a larger fraction is present in the protonated form HA.

• For weak acceptors, as the Fermi level moves torward the valence band edge, a larger fraction is not ionized:

  A ==> A^- + h⁺

  (i.e., by LeChatlier's principle, at high hole concentrations, most of the acceptor is present as A rather than as A^-.)