Reactive Ion-Assisted Deposition of Cerium Oxide Hole-Blocking Contact for Leakage-Current Suppression in an Amorphous Selenium Multilayer Structure

Cerium oxide has proven as a proper hole-blocking contact in multilayer amorphous selenium X-ray detectors to reduce leakage current by limiting hole injection. To further improve its blocking properties, one of the key factors is to prepare a thin layer of cerium oxide with full oxidation. In this paper, a cerium oxide thin film was deposited by reactive oxygen ion assisted e-beam evaporation that utilized an independent oxygen ion source to create ionized oxygen, allowing for a refined oxidation control without requiring high process temperatures. Compared with films obtained without ion-beam assistance, oxygen ion assisted deposition enhanced the refractive index of oxide film from ~1.8 to 2.2 at a wavelength of 550 nm and improved the electrical resistivity from ~10⁶ to 10¹⁰ Qcm. X-ray photoelectron spectroscopy and X-ray diffraction measurements further gave insights into the stoichiometry and the crystal structures. To investigate blocking effectiveness, multilayer selenium sandwich structures with and without the cerium oxide blocking contact were fabricated and the leakage current was evaluated.