Influence of unintentionally incorporated Ar atoms on the crystalline polarity of magnetron-sputtered Al-doped ZnO polycrystalline films on glass and sapphire substrates

The authors investigated the relationship between the content of incorporated Ar atoms and the crystalline polarity of polycrystalline Al-doped ZnO (AZO) films and examined the influence of this relationship on the resulting growth rate, crystallographic texture, and electrical properties. They deposited AZO films on glass and c-plane sapphire substrates via radio-frequency magnetron sputtering at substrate temperatures (T-s) of 100 or 200 degrees C using sintered AZO targets with an Al2O3 content of 2.0wt.%. The incorporation of a large amount of Ar atoms induced a change in the crystalline polarity from Zn-polar to O-polar, the latter of which is associated with numerous obstacles, such as a lower deposition rate, large residual compressive stress, and increased electrical resistivity. The authors demonstrated that increasing the T-s led to a reduction in the amount of unintentionally retained Ar atoms, thereby affording Zn-polar AZO films with their associated advantages.