Shallow n-type doping by transition-metal impurities (Hf, Zr, or Ti) in amorphous In2O3

Through first-principles electronic-structure calculations, we suggest that because the transition metal(TM)-d levels are located deep within the conduction band, TM (M = Hf, Zr, or Ti)-doped amorphous In2O3 (a-In2O3) can provide shallow donors, even though the effective mass of the a-In2O3 is slightly increased. We examined the microscopic structure of the doped oxides. The effective coordination number of In is little changed by the doping. The atomic structures of Sn, Hf, and Zr are similar, but the coordination number of Ti is smaller than those of the other dopants. The effective masses of the electron of the TM-doped a-In2O3 system are larger than those of the undoped a-In2O3 and Sn-doped a-In2O3.