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

采用氧还原的方法，以高硅掺杂的导电GaN体单晶作为旋转圆盘电极（RDE）电沉积ZnO薄膜。用Koutecky-Levich（K-L）法测定了70℃时KCl水溶液中氧还原反应的电荷转移速率常数（ORR）。结果表明：GaN（10-11）→ GaN（1-100）→ GaN（11-20）>GaN（10-12）>GaN（10-13）>>GaN（0001），ZnO在所有晶面上均实现了异质外延生长。从（11-22）衍射的XRD ω-扫描的半峰全宽（FWHM）检查exptaxy（镶嵌扩展）的水平，其顺序为GaN（1-100）>>GaN（10-11）>GaN（10-13）>GaN（11-20）>GaN（10-12）>GaN（0001）。ORR的活性越高，沉积的ZnO的单晶度越高。还检查了沉积电位的影响。较高的过电位导致较高的ZnO核密度，但它们是随机取向的。因此，可以理解，当电极活性高时，可以获得具有良好质量的ZnO，但是当施加大的过电位以增加沉积速率时，则不能获得具有良好质量的ZnO。

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.