阴极电沉积ZnO薄膜的取向控制生长

采用阴极电沉积法,在Zn(NO3)2水溶液中,以304不锈钢为衬底制备了ZnO薄膜,研究了Zn2+浓度和电流密度对ZnO薄膜择优取向的影响规律。XRD结果表明:随着Zn2+浓度和电流密度增大,ZnO薄膜逐渐由(002)面择优取向生长转变为(101)面择优取向生长;当Zn2+浓度为0.005mol.L-1、电流密度为2.0mA.cm-2或Zn2+浓度为0.05mol.L-1、电流密度为0.5mA.cm-2时,可以得到(002)面择优取向生长的ZnO薄膜;当Zn2+浓度为0.05mol.L-1、电流密度为2.0mA.cm-2时,可以得到(101)面择优取向生长的ZnO薄膜。根据二维晶核理论,通过分析不同生长条件下的过饱和度及其对ZnO的(002)型和(101)型二维晶核形核活化能的影响,对这一规律进行了解释。可见,通过改变Zn2+浓度和电流密度能够实现阴极电沉积ZnO薄膜的取向可控生长。

Orientation-controlling Growth of Electrodeposited ZnO Films on Cathode

It is important to control the orientation of ZnO film because many properties of ZnO film vary with its preferred orientation. Most of ZnO films ever reported are orientated towards c-axis. However, in the light-emitting application, nonpolar or semipolar ZnO films grown not along with c-axis are much preferable because the luminous efficiency of the c-axis orientated ZnO film is low due to the quantum confined Stark effect. Thus, the study of ZnO film grown along with other than c-axis is necessary. In this paper, ZnO films were fabricated on 304 stainless steel substrates by the cathodic electrodeposition in Zn(NO)3 aqueous solution, and the influences of Zn2+ concentration and the current density on the preferred orientation of the ZnO film were studied. X-ray diffraction results showed that as Zn2+ concentration and the current density increases, the preferred orientation of ZnO film changes from (002) to (101) gradually. When Zn2+ concentration is 0.005 mol·L-1 and the current density is 2.0 mA·cm-2, or Zn2+ concentration is 0.05 mol·L-1 and the current density is 0.5 mA·cm-2, the prepared ZnO films are (002) preferred orientation. When Zn2+ concentration is 0.05 mol·L-1 and the current density is 2.0 mA·cm-2, the prepared ZnO film is (101) preferred orientation. The phenomenon can be explained based on the two-dimensional nuclei theory. When Zn2+ concentration or the current density is low, the supersaturation of ZnO around substrate is also low and the nucleation activation energy of two-dimensional (002) nuclei is lower than that of (101) nuclei, therefore ZnO film is (002) preferred orientation. When Zn2+ concentration and the current density is high, the supersaturation of ZnO is also high and the nucleation activation energy of (002) nuclei is higher than that of (101) nuclei, therefore ZnO film is (101) preferred orientation. The results suggested that orientation-controllable growth of the cathodically electrodeposited ZnO films can be achieved by adjusting Zn2+ concentration and the current density.