Hydrogenation of the wide-gap oxide semiconductor as a room-temperature and 3D-compatible electron doping technique

A hydrogen atom, characterized by one unpaired electron and the smallest atomic radius, underlies the operations of various solid-state devices such as transistors, capacitors, solar cells, etc. Given its specific character as donor impurity in oxides, hydrogen may also facilitate efficient electron doping in a wide range of oxide devices. Here, we demonstrate room-temperature electrochemical hydrogenation of an archetypical oxide semiconductor (TiO2) thin film to achieve a 3D-compatible electron doping technique. The hydrogenated region can be precisely defined by photolithography without the influence of polycrystalline grain boundaries. Besides, secondary ion mass spectroscopy with deuterium isotope reveals considerable amount of hydrogen condenses around the TiO2 bottom interface indicating the critical influence of the interface on hydrogen stability. This hydrogen shows excellent stability in contrast to its high diffusivity in bulk TiO2, enabling robust electron doping for oxide thin film devices as well as suggesting stable interface hydrogen reservoir for electrochemical phenomena.