Tailoring the morphology, optical and electrical properties of DC-sputtered ZnO:Al films by post thermal and plasma treatments

Post thermal and plasma treatments are used to improve the morphology, optical and electrical properties of ZnO:Al (AZO) films prepared by DC-sputtering at room temperature. H-plasma treated sample exhibits the biggest surface roughness (Root Mean Square, RMS) of 6 nm in all the samples. All the films show high transmittance above 90% in 400-800 nm visible range. The ∼0.20 eV blue-shift of the band gap is observed both in H2 annealed and H-plasma treated samples due to the defect and grain boundary passivation by hydrogen introduction. The improvement of the electrical properties is obvious except for 500 °C O2 annealed sample (ρ=8.96×10−2 Ω cm, μ=5.50 cm2 V−1 S−1, and n=1.26×1019 cm−3) because of the extra oxygen substitution for vacancy oxygen (Vo) and the formation of oxides. The lowest resistivity (2.94×10−3 Ω cm) and highest mobility (12.00 cm2 V−1 S−1) are obtained after H-plasma treatment. The significant increment of the carrier concentration indicates that hydrogen atoms have been injected to the lattice during H-plasma processing. Such good textured surface morphology and transparent conductive properties suggest that AZO films have potential possibilities in thin film silicon (TFS) solar cell for light trapping.