Electrodeposition of semiconductors for optoelectronic devices: results onzinc oxide

Electrodeposition of polycrystalline semiconductor thin films is mainly use d for photovoltaic applications. Most of the work concerns chalcogenide com pounds like CdTe, CuInSe2, CdS... This route is also emerging for semicondu ctor oxide preparation. Results concerning the electrodeposition of zinc ox ide layers by reduction of dissolved oxygen in presence of Zn(II) ions are presented. Epitaxial growth can be achieved in zinc chloride solutions on s ingle crystal GaN layers. Bandgap (E-g) variations and effects on photolumi nescence are observed by changing the deposition conditions and post-deposi tion treatments. For instance, changing the potential from -1.1 to -1.5 V v ersus MSE in chloride solutions increases E-g from 3.4 to 3.55 eV. Changing chloride to perchlorate anions shifts E-g from 3.52 to 3.38 eV at -1.4 V. A thermal annealing in air further decreases the E-g down to the classical value (3.27 eV). This is correlated to a decrease in ZnO lattice parameters . A concomitant variation of the photoluminescence emission in the blue is observed. The highest yield is achieved on the epitaxial layers after annea ling (500 degrees C, 1 h). Specific aspects about the deposition mechanism are also discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.