Replacement and Rearrangement of an Oxide Lattice by Germanium Doping in Solution-Processed Indium–Zinc-Oxide Thin-Film Transistors

Germanium (Ge) doping effects on solution-processed indium-zinc-oxide (IZO) thin-film transistors (TFTs) were investigated. Ge doping increased the carrier concentration of Ge-doped IZO (Ge:IZO) thin films from 3.32 × 10¹⁴ to 3.13 × 10¹⁵ cm³ by Ge substitution for zinc (Zn). Ge easily substituted for Zn in the IZO active layer, due to its comparably small atomic radius. By this substitution, Ge doping provided additional valence electrons to the active layer, resulting in a value for the field-effect mobility of a Ge:IZO TFT that was almost two times greater than that of a pristine IZO TFT. Consequently, despite the Ge:IZO TFT being a quaternary system, it displayed a better electrical performance and stability at low processing temperatures, thus demonstrating the feasibility of this device for flexible displays.