Electrochemical Behavior of Semiconductors under Illumination

In contrast to metals, the average free energy of electrons can be changed in semiconductors to a great extent by illumination. Especially the concentration of minority electronic carriers can differ by orders of magnitude from the equilibrium value. This has two major effects on electrode processes: (a) change of charge distribution and potential drops in the space charge layer; and (b) variation of the rate of electrode reaction in which minority carriers are involved. Some examples are given for those effects at various semiconductors.