High mobility hydrogenated zinc oxide thin films

In this work we present a comprehensive study of the role of hydrogen in the structure, morphology, composition and electro-optical properties of zinc oxide thin films deposited by rf reactive magnetron sputtering at room temperature. The transparency and conductivity of the in situ hydrogenated zinc oxide films (ZnO:H) are improved with the addition of H₂ to the sputtering atmosphere, where the resistivity dropped one order of magnitude (from 3×10⁻² to 2.8×10⁻³ Ωcm) for an optimal dilution of 1.5% in argon. The effect of hydrogen in the conductivity of undoped ZnO thin films has been attributed to the shallow donor behaviour. However, we observed that the increase in the conductivity came essentially from the improvement of the mobility that reached 47.1 cm²/Vs for a carrier concentration of 4.4×10¹⁹ cm⁻³. This improvement in the mobility happens with an effective hydrogen incorporation into the bulk of the sputtered ZnO:H films, being attributed to the passivation of grain boundaries trap states while carrier concentration is dominated by the formation of Zn interstitials.