Hydrogen-plasma induced strongly-correlated transparent conducting titanate thin-films*

Transparent conducting oxides (TCO’s) are one of the key materials for optoelectronic device applications such as display panels and solar cells. Recently, strongly correlated complex oxide thin-films have been suggested as new TCO’s by utilizing the large effective mass of the conducting carriers. However, conventional chemical doping on complex oxides often results in unwanted impurity bands. Here, we present that epitaxial Ba_0.5Sr_0.5TiO₃ (BST) thin-films exhibit phase transitions from a wide-gap insulator to an Anderson insulator and eventually to a transparent conductor via hydrogen-plasma exposure (HPE). BST thin-films are well-known robust insulators; no chemical doping methods can generate conducting carriers. Our pulsed laser deposited BST thin films on GdScO₃ substrates are optically transparent. After about 3 minutes of HPE, the samples exhibit an absorption band at infrared energies. Further HPE up to 5 minutes exhibits a Drude response in the optical conductivity. The transparency of HPE BST thin-films remains the same as unexposed samples below 1.5 eV. We will discuss how HPE can open a new way for generating TCO’s.