Light-induced conversion of an insulating refractory oxide into a persistent electronic conductor

• Published in: Nature (London) Vol. 419; no. 6906; pp. 462 - 465
• Main Authors: Hayashi, Katsuro, Matsuishi, Satoru, Kamiya, Toshio, Hirano, Masahiro, Hosono, Hideo
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 03.10.2002; Nature Publishing Group
• Subjects: Absorption; Atmosphere; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electronic transport in condensed matter; Exact sciences and technology; Ions; Irradiation; Materials science; Metals; Mixed conductivity and conductivity transitions; Optics; Oxides; Physics; Superconductivity; Ultraviolet radiation; Inorganic compounds; Electrical conductivity; Heat resistant materials; Dielectric materials; F centers; Ternary compounds; Photoinduced effect; Color centers; Experimental study; Calcium oxides; Complex impedance; Ultraviolet radiation; Electronic conduction; Illumination; Absorption spectra; Aluminium oxides; Absorption edge
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature01053

Materials that are good electrical conductors are not in general optically transparent, yet a combination of high conductivity and transparency is desirable for many emerging opto-electronic applications. To this end, various transparent oxides composed of transition or post-transition metals (such as indium tin oxide) are rendered electrically conducting by ion doping. But such an approach does not work for the abundant transparent oxides of the main-group metals. Here we demonstrate a process by which the transparent insulating oxide 12CaO·7Al2O3 (refs 7-13) can be converted into an electrical conductor. H- ions are incorporated into the subnanometre-sized cages of the oxide by a thermal treatment in a hydrogen atmosphere; subsequent irradiation of the material with ultraviolet light results in a conductive state that persists after irradiation ceases. The photo-activated material exhibits moderate electrical conductivity (∼0.3 S cm-1) at room temperature, with visible light absorption losses of only one per cent for 200-nm-thick films. We suggest that this concept can be applied to other main-group metal oxides, for the direct optical writing of conducting wires in insulating transparent media and the formation of a high-density optical memory.