Using Intermittent Process to enhance the optoelectronic properties of Ga-doped ZnO thin films

Gallium doped ZnO (GZO) as Transparent conductive oxide (TCO) is poison less and cheaper than Indium Tin Oxide (ITO) [1], which will have the opportunity to take place it. Un-doping ZnO has poor electrical properties [2], but the quality of thin film will be influenced after doping. Depend on this, lots of researches have tried to solve this problem such as thermal annealing after grown thick films, grown a buffer layer, embedding a metal layer and so on [3], which can perhaps improve the optoelectronic properties, but also increase the cost for grown processes. In this study, the "Intermittent Process" is designed to enhance the quality of thin film and also optoelectronic properties. The intermittent process is defined to insert the intermittent time during growing thin film to form multiple layers. Therefore, there are two main parameters, which are intermittent number (IN) and intermittent time (IT). The different intermittent numbers (IN) as 0, 1, 2, 3, 4 and intermittent time (IT) are 5, 7.5, 10, 12.5, 15 minutes 4 had been chosen. After the optimum IN and IT are studied, the substrate heating will also be used during Intermittent Process, which include 300°C, 400°C, 500°C. The comparison between as-grown sample and the thin film with optimum parameters treatment is shown in table1. The SEM images as figure 1 show the results of the surface structure after different treatments. After Intermittent Process and substrate heating, the surface of GZO thin film become more compact and smoother, which means the optoelectronic properties of thin film could be enhanced due to the larger grain size reduced the grain boundary and made the light and electron easy to transmit. In order to demonstrate the phenomenon of Intermittent Process can lead a better condition for deposition, the cross-section HRTEM is measured as shown in Figure 2. [4]. In the beginning of buffer layer shown in Figure 2(b), lots of disordered structures are clearly observed. Better crystalline structures are clearly observed after the intermittent structures as shown in Figure 2(c). Based on this analysis of the atomic resolution TEM image, the Intermittent Process is proven to effectively improve the quality of thin film.