Al-impurity-doped transparent conductive oxide films of In 2O 3−ZnO system

Abstract

The effects of Al 2O 3 dopings in pseudobinary (In 2O 3) 1− δ (2ZnO) δ films were investigated, and carrier generation mechanism was discussed. Here the δ value is the ratio of Zn/(Zn+In). For Al 2O 3 doping below 2 wt%, low-resitivity amorphous films in 2–4×10 −4 Ω cm were deposited over a narrow range of δ=Zn/(Zn+In) (0.2⩽ δ⩽0.4). At Al 2O 3=2 wt% doping, the resistivity was improved in the same narrow range of δ. Using a ZnO:Al target with 3 wt% Al 2O 3, film resistivities of 2–4×10 −4 Ω cm were attained over a relatively wide range of δ in the amorphous phase (0.2⩽ δ⩽0.6). This result was due to the increase in carrier concentration at δ=0.3–0.6. The Al 2O 3 doping also influenced on optical band gap: band gap shrinkage for Al 2O 3=2 wt% and band gap widening for Al 2O 3=3 wt%. For homologous crystalline films, Al 2O 3 doping decreased carrier concentration, independent of the level of Al 2O 3 doping. The Al 2O 3 doping increased linearly optical band gap energy. These results indicate that the Al atoms are impurities that distort the lattice in homologous film.