Keywords: TCO, transparent conducting oxides, amorphous In-Zn-O, IZO, conductivity, optical transparency, indium zinc oxide, thin films, nanotechnology, oxygen
Conductivity and transparency in amorphous In-Zn-O transparent conductors
Amorphous indium zinc oxide (a-IZO) is an increasingly important material both as a transparent conductor or semiconductor in transparent electronics and as an archetype amorphous electronic mixed metal oxide in itself. Here, a co-sputtering composition spread combinatorial approach was used to examine the conductivity and optical transparency in a-IZO thin films as a function of both In : Zn metals stoichiometry and the amount of oxygen added to the argon sputter gas. For optimising the conductivity, the percent oxygen in the sputter gas and the metals composition were found to have a strongly coupled effect. In particular, a-IZO films with conductivity σ > 2000 S/cm can be grown for a broad range of metals compositions, In content from ∼60 to ∼85 cation%, as long as the corresponding optimal oxygen level is used in the deposition. The amount of oxygen required increases with increasing indium content. When too much oxygen is used, the conductivity is reduced due to a decreased carrier concentration whereas when too little oxygen is used, the conductivity is reduced due to decreased electron mobility. Concurrent with the decrease in electron mobility, there is increasing optical absorption from 400 nm to 1000 nm which renders the oxygen deficient a IZO samples grey.