The synthetic semiconducting diamond electrode: A photoelectrochemical estimation of the diffusion length

Abstract

The synthetic diamond is a new electrode material: systematic investigation of it is still at an early stage. The CVD-grown films are moderately conductive when prepared under certain special conditions as the material is a p-type semiconductor [l] (although the nature of the acceptor, introduced during film growth, is still unclear). Thin-film polycrystalline diamond electrodes have been proven to be fairly stable in aqueous solutions; they are sensitive to visible and near-UV light [l]. Impedance spectroscopic studies have revealed that polycrystalline diamond thin films are microheterogeneous structures consisting of rather conductive diamond grains (crystallites) separated by less conductive intergrain boundaries (hypothetically consisting of amorphous carbon). Specific conductivities of the grains and intergrain boundary material were estimated as 1O-4 and lo-’ QR-’ cm-‘, respectively [2]. In this paper the diffusion length of minority carriers in polycrystalline diamond films is estimated from photopotential measurements. Diamond is a very wide-gap semiconductor (E, = 5.5 eV>; therefore, the photoeffects produced by visible and near-UV light cannot be caused by interband electron transitions. Moreover, the shape of the action spectrum of the photocurrent [l] makes it possible to explain the photoeffects by transitions of photo-excited electrons to or from the local levels situated within the bandgap. These levels may be caused by impurities or defects of the crystal structure, introduced during film growth.