Influence of oxygen and argon flow on properties of aluminum-doped zinc oxide thin films prepared by magnetron sputtering

• The aluminum-doped zinc oxide films were prepared by RF-magnetron sputtering.
• The average transmittance of the samples was above 89% in the range of 400–900 nm.
• The films deposited at low oxygen pressure showed low resistivity.
• The grain size and thickness of films were studied.

In this study, the influence of the oxygen/argon (O2/Ar) flow ratio on aluminum-doped zinc oxide (ZAO) films using a Zn1.22Al0.02O1.25 target was investigated systematically. Different samples were obtained by changing the O2/Ar flow ratio from 0.11 to 3. The grain size first decreased and then increased as the O2/Ar flow ratio increased, reaching a minimum size of 8.53 nm at a flow ratio of 1. All films showed different average transmittances above 400 nm because of different surface structures and film thicknesses; the thickness of films varied from 261 to 897 nm. Moreover, the ZAO films exhibited different optical bandgaps between 3.22 eV and 3.31 eV. The resistivity first increased from 2.1 × 10− 4 Ωcm to 350 × 10− 4 Ωcm and then decreased to 220 × 10− 4 Ωcm with increasing O2/Ar flow ratio. Both the carrier concentration and Hall mobility first decreased from 5.6 × 1020 cm− 3 to 0.3 × 1020 cm− 3 and from 3.9 cm2/Vs to 0.6 cm2/Vs, respectively, and then increased to 0.9 × 1020 cm− 3 and 1.1 cm2/Vs, respectively, with increasing O2/Ar flow ratio.