Effect of boric acid content on the structural and optical properties of zinc oxide films prepared by spray pyrolysis technique

ZnO is a very interesting material for many different applications in both microelectronic and optoelectronic devices. It is a wide-bandgap oxide semiconductor with a direct energy gap of about 3.37 eV. As a consequence, ZnO absorbs UV radiation due to band-to-band transitions. However, it can be used as transparent conductive oxide (TCO) thin films, mainly for applications such as solar cells, liquid crystal displays and heat mirror. Furthermore, ZnO is used as semiconducting multilayers, photothermal conversion system, gas sensors, and optical position sensors. In the thesis study, Boron doped ZnO films were prepared by spray pyrolysis technique at 450 °C substrate temperature, which is a low cost and large area technique to be well-suited for the manufacture of solar cells, using Boric acid (H3BO3) as dopant source, and their properties were investigated as a function of doping concentration. X-ray analysis showed that the films were polycrystalline fitting well with a hexagonal structure and have preferred orientation in (002) direction. And optical band gap of the undoped and Boron-doped ZnO films were found to vary from 3.46 to 3.29 eV. The changes observed in the energy band gap and structural properties of the films related to the Boric acid concentration are discussed in detail. Inthe thesis study, the structural and optical properties of undoped and doped ZnO films obtained by the spray pyrolysis technique shows that they are strongly dependent on the Boron concentration. Particularly,it was observed that the best crystallinity of ZnO films is obtained at the atomic percentage of dopants in (B/Zn) solution at %1.0. It was determined that the films have polycrystalline structures and show a preferential orientation along (002) with well-defined microstructures. It was observed that Boron incorporation (at 1.0%) caused the crystallinity levels to increase.It was determined that the crystallizationlevelis low at higher doping level (3.0% and 5.0 %) due to the increasing grain boundaries which behave as defects in the structure affecting the structural properties of the films. From the XRD analyses it was concluded that Boron incorporation plays a significant role in the crystalline and structural properties of the ZnO films, and 1.0% Boron incorporations are the most suitable Boron amounts.