Transport properties of non magnetic and magnetic ZnO thin films under field effect

The integration of ZnO based high mobility transparent semiconductors with perovskites that exhibit a wide spectrum of physical properties (superconductivity, ferroelectricity, ferromagnetism, etc.) may lead to a wide variety of new electronic/optoelectronic devices; recently we reported about the realization of epitaxial ZnO/SrTiO3 heterostructures and about their application in the fabrication of field effect transistors transparent at visible wavelength. As further development in this field, here we present the results about the deposition of high crystalline quality Al or Co doped ZnO films grown by pulsed laser deposition on 110 face of strontium titanate single crystals. Field effect (FE) experiment, allowing to change the carrier concentration of the film by more than 4 orders of magnitude (from 1015 to 1020 e-/cm3 estimated by Hall effect measurements under FE), were employed to deeply investigate transport mechanisms. In particular, we observed a crossover of low temperature magnetoresistance from a negative behaviour in accumulation state to a positive one in depletion state. The measure of the activation energy as a function of the Gate potential allowed us to get information on the density of states.