STRUCTURAL AND OPTICAL PROPERTIES OF ZNO NANOSTRUCTURES

Abstract

The structural and crystal quality of ZnO film, Au-catalyzed ZnO nanowires (NWs) and catalystfree ZnO NWs were studied. ZnO film deposited at 145 ^oC by atomic layer deposition (ALD) had a smooth surface (RMS roughness: 2.850 nm), high transmittance in the visible light region (89.9±6.7%) and good film resistivity (4.131x10^-3 Ω.cm). Thus, ZnO films with these attractive properties are suitable for transparent conducting oxide (TCO) applications. Both catalyst-free ZnO NWs and Au-catalyzed ZnO NWs were grown using chemical vapour deposition (CVD). Vertically aligned ZnO NWs (catalyst-free) could be synthesized using highly (002) oriented ZnO seed film pre-deposited on silicon substrate. The catalyst-free ZnO NWs exhibited the best crystal quality as it showed the largest percentage of Zn-O bonds in XPS analysis and highest UV/visible ratio in PL measurement. However, randomly grown Au-catalyzed ZnO NWs were synthesized on bare silicon substrate. The randomly grown NWs has been attributed to the large lattice mismatch between ZnO and silicon wafer. The growth of Au-catalyzed ZnO NWs was proposed to be governed by Vapour-Liquid-Solid_Vapour-Solid (VLS-VS) mechanism.