SEMICONDUCTOR PROPERTIES OF ANODIC SULFIDE FILMS ON ANTIMONY
Doctor of Philosophy
Anodic sulfide films on antimony metal have been studied in relation to their electrochemical and photoelectrochemical properties. The formation of the anodic films in aqueous hydrosulfide solutions has been investigated using potentiodynamic, galvanostatic and potentiostatic techniques. The sulfidation mechanism and the efficiency of charge storage in the surface phase was found to be strongly dependent on the electrode potential and current density. The initial stages of formation followed a high field growth process involving ionic migration through the film. For thicker films, the growth rate was controlled by a chemical step involving mass transport and nucleation processes. Metal dissolution accompanied film formation under most growing conditions. The electronic and potential distribution at the sulfide/solution interface have been examined using a. c. impedance measurements. The charge distribution across the film exhibited a strong influence on the electrochemical behavior of the system. A band model has been used to describe the potential arrangement in the space-charge region near the surface. The sulfides possessed n-type semiconductor properties and this conductivity has been correlated to their non-stoichiometric nature. The donor density has been estimated from Mott-Schottky plots to be approximately 2 x 10('20) cm('-3). The solid-state characteristics of the films were investigated using photocurrent and photopotential methods. The development of photosensitivity has been discussed in relation to the growth behavior. The optical properties that give rise to the photoactivity has been determined from the spectral response of the photoeffects. The light absorption process has been found to involve phonon assisted excitations. The fundamental band edge for the indirect transitions was calculated to be near 1.77 eV.