Amorphous CaAlO_x Thin Film as Transparent Conducting Oxide

Transparent conducting oxides (TCO) has been an important constituent in modern opto-electronic devices. To satisfy competing demands, approaches of increasing carrier concentration in a wide-bandgap semiconductor through heavy doping, in case of tin-doped indium oxide, have been employed. Based on the various degrees of freedom in fabrication, e.g. chemical composition, crystallography and epitaxial strain, diverse methods for engineering of transparent window and conductance of TCO have been reported. The modulation of orbital state involved in the chemical state of thin film can give rise to high conductivity nature even in amorphous material which could be in good use as flexible electronics.
In this presentation, we propose amorphous flat calcium aluminate (CaAlO_x, CAO) as a new TCO with a high electronic mobility and a wide transparency window. We fabricated CAO thin films using pulsed laser deposition. The resistivity of the thin films could be systematically modified by controlling the chemical composition, and for the thin films annealed at 10^-5 Torr, the resistivity was as low as 57 μΩ cm at room temperature. The surprisingly high performance of the new TCO deserves discussion on the electronic structure of amorphous thin films.