Photocontrolled Surface Conductance in Anodized InSb

Abstract

Anodized p‐type InSb, cooled to the extrinsic conduction range in the dark, was found to have an n‐type inversion layer at the surface. Illumination changes the n‐type inversion layer to a p⁺ accumulation layer; any intermediate surface condition can be obtained by controlled exposure. A method for determining the surface conductance of the inversion layer is described. This method utilizes a high‐impedance grain boundary barrier to avoid shunting of surface conduction by bulk conduction. The highest surface conductance on unilluminated anodized samples was found to be 100 μmhos/square. Spectral response measurements show that photons in the energy range 0.8 to 3.5 eV are effective. The effect is believed due to photoemission of electrons from the InSb into the oxide. Transient response measurements for light on and off conditions on n‐ and p‐surfaces support this model.