Tunable‐Conduction‐Band In–Zn–O‐Based Transparent Conductive Oxide Deposited at Room Temperature

Abstract

Aluminum (Al)‐doped indium zinc magnesium oxide (Al:IZMO)‐based transparent conductive oxide (TCO) films with a tunable conduction band structure are developed via deposition at room temperature under radio‐frequency (RF) magnetron co‐sputtering for the application of highly efficient photovoltaic devices. First, at the amorphous phase region with the [In]/([In] + [Zn]) compositional ratio of 0.5–0.8, Al‐doped indium zinc oxide (Al:IZO) films obtained by introducing a small amount of aluminum oxide (Al2O3) exhibit higher Hall mobility and lower carrier density than those of indium zinc oxide (IZO) without Al doping. Second, adding magnesium oxide (MgO) to Al:IZO allows the optical bandgap (Eg) control, with constant ionization energy of −7.31 eV, which can be expressed by Eg = 0.83y + 3.33 (eV) as a function of [Mg]/([Zn] + [Mg]) compositional ratio (y) (in the y value region of 0–0.12). This result suggests that the conduction band minimum can be tuned by 0.067 eV under the 8% Mg substitution into the Zn site in the Al:IZMO films while remaining valence band maximum. Al:IZMO‐based TCO films with conduction band controllability are deposited at room temperature for preventing thermal damage. These findings contribute to the device design and development of emerging photovoltaic applications.