Structural improvement of zinc oxide films produced by ion beam assisted reactive sputtering

Reactively sputtered zinc oxide thin films exhibit low crystalline order when deposited on unheated substrates. To improve the structural order, films are usually deposited onto heated substrates at temperatures of about 200-300 degrees C. Nevertheless, techniques that enable room temperature deposition of ZnO films with high structural quality would be advantageous. In this work ion bombardment from an auxiliary ion gun during film growth is employed to improve the crystalline quality. Xe+ ion bombardment under appropriate conditions leads to the growth of films with high crystalline order. Based on our structural investigations employing x-ray diffraction, atomic force microscopy and transmission electron microscopy, a growth model is proposed which explains the impact of ion bombardment on the structural evolution. We prove that it is especially the nucleation stage of the growth process which is susceptible to this ion bombardment.