ELECTROLUMINESCENCE TRANSIENT AND ITS APPLICATION TO KINETIC-STUDY ON ELECTRODE-REACTIONS CAUSED BY CARRIER TUNNELING IN SEMICONDUCTOR ELECTRODES

A new method for studying electrode kinetics at a semiconductor-electrolyte interface is proposed. An n-type semiconductor is first put at the depletion mode by a large anodic bias V-A with which a majority carrier (electron) tunneling takes place from the electrolyte to the semiconductor, leaving reaction (oxidation) intermediates such as A-->A*+ e(-). When the semiconductor is put at the accumulation mode by a large cathodic bias V-C, after some time interval T-0 during which the external bias is kept 0 V, the electron transfer from the conduction band to the intermediates produced during anodic period takes place, accompanying light emission (electroluminescence). By varying T-0, the lifetime of the intermediates (A*) can be estimated. Practical measurements were made by using polycrystalline TiO2 prepared by the sol-gel method, which allowed a large tunnel current. It was found that oxidation intermediates disappeared from the surface by a second-order chemical reaction with a half-life of about 5000 s.