Al-doped ZnO (AZO) thin films were

Al-doped ZnO (AZO) thin films were deposited on normal glass substrates in pure Ar atmosphere using unbalanced RF magnetron sputtering technique from AZO (ZnO: 98 wt% and Al2O3: 2 wt%) ceramic target that was high purity of 99.999%. Fig. 1 presents a schematic diagram of the unbalanced RF magnetron sputtering system of AZO films with extended plasma towards the substrate. The RF system consists of solenoid coils, which were placed around the sputter target. The unbalanced magnetic field can be generated through the supply of electric current to the solenoid coils. Under certain applied currents, the resulting magnetic field distributes the plasma towards the vicinity of the substrate and it enhances the ion flux density through electron transportation along the helical path around the magnetic field lines with induced ionization. During the film deposition, the substrates were kept at room temperature. Prior to film deposition, the glass substrates were treated ultrasonically with acetone and distilled water successively for 10 min at 30 °C, then blown with highpressure nitrogen gas and finally dried on hot plate at 100 °C for 5 min. The rotating substrate holder was placed at 15 cm from the sputter target. RF sputter power of 100 W was maintained constantly to the AZO target throughout all experiments. The deposition chamber was pumped down to a pressure of 5 106 Torr, using a pumping system consists of oil-sealed rotary pump coupled with a turbo molecular pump. Highly purified argon gas was introduced directly into the deposition chamber at a flow rate of 30 sccm through a fine mass flow controller. During the film deposition, the working pressure was held constant at 4.3 103 Torr for the duration of 30 min. The pre-sputtering process was performed for 10 min in Ar ambient to remove the other contaminants present on the surface of the target. The external magnetic field from 0 to 6.0 mT (0, 3.0 and 6.0 mT) has been developed by fine-tuning of electrical current to the coaxial solenoid coils from 0 to 0.2 A (0, 0.1 and 0.2 A) respectively. The magnitude of external magnetic field was produced by the coaxial solenoid coils which consists of 3500 turns of Cu wire and they were mounted around the conventional RF magnetron source. With effect of solenoid coil current, the magnetic field lines can be extended and confined near the substrate surface, which would have a much greater impact on the sputter ion density. The AZO films deposited at various magnetic fields are further denoted as AZO-magnetic field in mT, e.g., AZO-0 (magnetic field: 0 mT).