Silicon https://doi.org/10.1007/s12633-017-9686-y ORIGINAL PAPER Impact of Silicon Doping on the Properties of Transparent Conducting CdO Thin Films A. A. Dakhel 1 Received: 11 September 2017 / Accepted: 13 November 2017 © Springer Science+Business Media B.V., part of Springer Nature 2018 Abstract CdO thin films doped with different amounts of silicon ions have been deposited on glass substrates by the vacuum evaporation method in order to improve their properties for application as transparent conducting oxide (TCO) films. The structural, electrical, and optical properties of the host CdO films were systematically studied. The realization of doping with silicon ions was confirmed and studied by the X-ray diffraction (XRD) method. It was concluded that Si ions occupied locations in interstitial positions and structural vacancies of the CdO lattice. The bandgap of Si-doped CdO was blue shifted following the Moss-Burstein (B-M) effect. The dc-electrical behaviors were studied by the Van der Pauw method showing that the prepared Si-doped CdO films were degenerate semiconductors of controllable opto-electrical properties by doping level. The utmost improvements in mobility (μ) and conductivity (σ ) took place with the host CdO film doped with ∼2% Si, so that the mobility increased by ∼10 times and the conductivity by ∼100 times compared to the pristine CdO film. The results show that silicon is effective for CdO utilization in applications in the TCO field. Keywords Cadmium-silicon oxide · Si-doped CdO · CdO films 1 Introduction Cadmium oxide (CdO) is a transparent conducting oxide (TCO) that can be used in the optoelectronic field of applications like fabrication of solar cells, flat panels, phototransistors, as well as other types of applications as in the field of gas sensing [1–3]. The unique electro-optical properties of CdO stand behind those applications. Thin films of CdO are partially transparent to the visible and NIR spectral regions with a direct bandgap of about 2.2–2.7 eV [1, 3, 4]. The electrical conductivity of CdO is mainly caused by its natural non-stoichiometric cadmium interstitials and oxygen vacancies. Therefore, the CdO material has n-type degenerate semiconducting properties with low resistivity of about 10 −2 –10 −3 .cm [3].  A. A. Dakhel adakhil@uob.edu.bh 1 Department of Physics, College of Science, University of Bahrain, P.O. Box 32038, Sakhir, Kingdom of Bahrain On the other hand, the high demand for the opto- electronic devices requires continuous development in the optical and electrical properties of TCOs. In addition, the development of TCO properties [conductivity (σ ), mobility (μ) and optical transparency] is considered as a compromise between high transmittance and low resistivity. So it is supe- rior to improve the optoelectronic properties by improving the carrier mobility (μ) rather than increasing the carrier concentration (N el ), because the increasing of N el causes reduction in the optical transparency of the film. The electro-optical properties of CdO films could be controlled and developed by the method and conditions of synthesis, including doping with exotic ions. It was observed that the sizes of dopant ions have a great influence on the resultant host CdO properties [3]. From that point of view, a practical conclusion was accomplished that when the sizes of the dopant ions are slightly less than that of the Cd 2+ ion (0.095 nm [5]), the conductivity of the host CdO will be increased. Moreover, the doping with ions of much smaller sizes than that of Cd 2+ ions, like boron B 3+ ions (0.027 nm) [6], Al 3+ ions (0.0535 nm) [7–9], or Ti 4+ ions (0.0605 nm) [10], will lead to improvement of all the electronic parameters especially the carrier mobility.