Influence of buffer layer on optoelectronic properties of B-Mg co-doped ZnO ultrathin film for high-performance transparent conductor application

In order to develop transparent conductors for optoelectronic devices, B-Mg co-doped ZnO (BMZO) thin films and ZnO/BMZO bilayer films were prepared by using a magnetron sputtering system in this work. The properties of the films with varying operating pressure and buffer layer thickness were measured and investigated systematically. It is found that all films have high transparency, which are almost independent of the buffer layer thickness and the working pressure. Working pressure affects the chance of collision between sputtered particles and gas molecules, which impacts on the average free range of sputtered particles and the energy of the particles. Thus, the BMZO films with high crystallinity and low resistivity can be obtained at appropriate working pressure. The introduction of ZnO buffer layer makes the BMZO films more suitable for TCO applications compared to monolayer BMZO. The results showed that the thickness of the buffer layer with the introduction of ZnO buffer layer decreased the surface roughness and internal stress of the films, which increased the electrical and optical properties of the film. In particular, the ZnO/BMZO film prepared at a working pressure of 3 Pa, exhibits the optimized optoelectrical properties when the buffer layer thickness is 12 nm.