Interface analysis of KN and NN by XPS measurements
Many electronic devices are based on lead containing materials, such as PZT. Since at least the European Union decided to ban toxic materials from electrical and electronic equipment and to substitute these materials by safer materials, lead free materials have been attracting more and more interest. Especially potassium niobate (KN) and sodium niobate (NN) based materials look promising for applications, such as power electronic capacitors, which are necessary in the field of renewable energies and electromobility [1–3]. In these devices, interfaces, in particular semiconductor-metal interfaces, play an important role because they determine the charge transport properties. These properties are defined by the band alignment and the Schottky barrier height of two materials, respectively. Furthermore, it is important to have knowledge about the Fermi level range within a material for electronic device engineering. In order to understand the accessible Fermi level range in KN and NN X-Ray Photoelectron spectroscopy (XPS) measurements have been performed. In this context, several oxidizing and reducing treatments, such as oxygen plasma and water exposure, have been applied. Schottky barrier heights to ITO and RuO2 have been investigated by conducting interface experiments. All these treatments and the subsequently XPS measurements have been performed in-situ. Experiments were done on both, ceramic and thin film samples. Furthermore, potassium sodium niobate (KNN) thin films, have been investigated. In order to change the Fermi level of a material and, therefore, control the electrical properties, dopants can be introduced into a materials system. In this regard, donor doped NN ceramics, such as Sr- and Ca-doped samples, have been conducted. All the results obtained by XPS measurements are compared to the electrical properties of the materials.