Pulsed laser deposition of transparent ZnO/MgO multilayers

We report on the structural, optical and electrical properties of ZnO/MgO multilayers grown by pulsed laser deposition technique. The film thickness of ZnO sublayer (t(Zno)) was found to have great impact on the properties of ZnO/MgO multilayers. Investigations reveal the structural phase transition from wurtzite phase to cubic phase with corresponding decrease in ZnO thickness. The optical transmittance of the multilayers is over 80% in the visible region and there is a gradual shift of absorption edge towards a longer wavelength with corresponding increase in ZnO sublayer thickness. Two absorption bands at around 400 nm and 270 nm were observed in the transmission spectra of ZnO/MgO multilayers for similar ZnO and MgO layer thickness, which has been ascribed to phase separation to hexagonal and cubic phases. The calculated optical band gap E-g shows a widening from 3.51 eV to 6.23 eV with corresponding decrease in ZnO sublayer thickness from 100 nm to 23 nm, which in turn leads to an increase in resistivity in ZnO/MgO multilayers. These results provide important information for the design and modeling of ZnO/MgO optoelectronic devices due to their adjustable bandgap energies. (C) 2010 Elsevier B.V. All rights reserved.