We examine how the photo-induced carriers contribute the thermoelectric transport, i.e. the nature of the photo-Seebeck effect, in the wide-gap oxide semiconductor ZnO for the first time. We measure the electrical conductivity and the Seebeck coefficient with illuminating light. The light illumination considerably changes the Seebeck coefficient as well as the conductivity, which is sensitive to the photon energy of the illuminated light. By using a simple parallel-circuit model, we evaluate the contributions of the photo-induced carriers to the conductivity and the Seebeck coefficient, whose relationship shows a remarkable resemblance to that in doped semiconductors. Our results also demonstrate that the light illumination increases both the carrier concentration and the mobility, which can be compared with impurity-doping case for ZnO. Future prospects for thermoelectrics using light are discussed.Comment: 5 pages, 4 figures, to be published in J. Phys. Soc. Jp

We have measured the Seebeck coefficient and the resistance under light illumination of 365 nm in a ceramic sample of ZnO at 100, 150, and 200 K, and have analyzed the photo-Seebeck coefficient and the photoconductivity using a two-layer model. We have evaluated the photo-doped carrier concentration from the magnitude of the photo-Seebeck coefficient to be of the order of 1019 cm−3, as is similar to the case of thin-film and single-crystal samples. The photo-doping effects are compared among ceramic, single crystal, and thin-film samples.