Saturation of the photoresponse in Nd0.67Sr0.37MnO3-delta epitaxial layersclose to the metal-insulator transition

Internal electrical fields of different origin are observed in the semicond ucting regime of Nd2/3Sr1/3MnO3-delta epitaxial layers and are assigned to thermoelectric effects and to an ambipolar charge distribution in trap stat es, following a photogeneration of electron-hole pairs. In particular, if t he resistivity shows a double peak, the photoresponse shows saturation in t he regime of the low-temperature peak, suggesting the existence of a gap in the transitional regime of the metal-insulator transition. (C) 1999 Elsevi er Science B.V. All rights reserved.