Multi directional epitaxial electrodeposition of ZnO thin films on bulk GaN single crystals

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Heavily Si-doped conductive GaN bulk single crystals were used as a rotating disk electrode (RDE) to electrodeposit ZnO thin films employing the reduction of oxygen. Charge transfer rate constants for oxygen reduction reaction (ORR) were determined from the I-V curves in KCl aqueous solution at 70℃ by Koutecky-Levich (K-L) analysis. The order of GaN(10-11)〓GaN(1-100)〓GaN(11-20)>GaN(10-12)>GaN(10-13)>>GaN(0001) was found. Heteroepitaxial growth of ZnO was achieved for all crystal faces. The level of exptaxy (mosaic spread) was checked from the full-width at half maxima (FWHM) of the XRD ω-scan for the (11-22) diffraction and was in the order of GaN(1-100)>>GaN(10-11)〓GaN(10-13)>GaN(11-20)>GaN(10-12)>GaN(0001). The higher activity for the ORR approximately resulted in the higher single crystallinity of the deposited ZnO. The effect of the deposition potential was also checked. The higher overpotential resulted in the higher density of ZnO nuclei but they were randomly oriented. It is therefore understood that ZnO with good quality can be obtained when the electrode activity is high, but not when a large overpotential is applied to increase the rate of deposition.