SPECTRALLY SENSITIZED PHOTOCONDUCTIVITY OF ZINC OXIDE CRYSTALS*

Abstract

Abstract— Spectral sensitization of photoconductivity was found after coating single crystals with an organic dye in a methanol solution. Similar experiments have been carried out under conditions designed to exclude the influence of solvent and adsorbed gases. The dye was deposited from vapor onto clean crystal surfaces in ultrahigh vacuum and the spectral distribution of the photoconductivity was observed without admission of air. With both methods of dyeing, the quantum yields, referred to the absorbed light, were comparable to the yield in the intrinsic region. Also the influence of a transverse electric field upon surface conductivity before and after dyeing was studied. From the ‘field effect’ it is concluded that the adsorbed dye causes a considerable increase of the density of electronic surface states near the Fermi level.