Influence of interband transition on the laser-induced voltage in thermoelectric CaxCoO2thin films

Abstract

Laser-induced voltages in incline-oriented thin films of thermoelectric Ca${}_{x}$CoO${}_{2}$ have been investigated at four laser wavelengths. Large film in-plane voltage signals, several tens of volts, were identified at each wavelength regardless of the occurrence of interband optical transition. The thermal model based on heat conduction equation demonstrates that this transverse voltage is closely related to heat conduction normal to the film surface and, hence, that it is associated with a phenomenon called the off-diagonal thermoelectric effect. However, distinct discrepancies between the experiment and the thermal model were identified for short laser wavelengths at which interband transition occurred. We discuss the discrepancies in terms of a photovoltaic effect (the photo-Dember effect), showing that the laser-induced voltage may not be purely thermal in origin when it is accompanied by interband transition.