抄録
ZnO powders have been prepared chemically from zinc-sulfate, chloride, nitrate and acetatevia zinc oxalate and their photoconductive properties have been studied comparing with those of a commercial ZnO powder for photoreceptor use prepared by a physical process, i. e., oxidation of vapor of zinc. Effects of metal doping and firing temperature of the zinc oxalate on the photoconductivity of the ZnO powders have also been studied. The dark and photo-conductivity of the ZnO powders were measured using a surface type electrode without binder. All the measurements were made by the dc method in an evacuated chamber.
All the undoped ZnO powders showed photosensitivity to UV light, but the photosensitivities depended on the starting materials. The photosensitivity of the commercial ZnO powder is higher than those of the undoped ZnO powders prepared in this study. Doping of metals such as Cr, Na and Pb did not extend the photoconductive spectra to the longer wavelength region but increased the photosensitivity.
The activation energy for the dark conduction is 1.7 eV for the commercial ZnO, indicating the intrinsic conduction, while those are in the range of 0.36 to 0.52 eV for undoped ZnO in this study, indicating the extrinsic conduction. According to the TSC measurements, it has been confirmed that the ZnO powders with deeper traps are less photosensitive.
The most eminent difference in the photoconductive behavior between the chemically prepared ZnO and the commercial one is the rise and decay characteristics of the photocurrents. The photoresponse of the former is fast, while those of the later are very slow.
