Effect of different sputtering gas mixtures on the structural, electrical, and optical properties of p-type nio thin films

We investigated how mixtures of Ar and 0₂ or N₂ gases affect the structural, electrical and optical properties of RF-magnetron-sputtered NiO films. It is shown that the addition of 0₂ gas to Ar ambient (namely, Ar:o₂=2:1 to 1:2) slightly reduces the (2 0 0) texturing of the NiO films. The introduction of N₂ gas (from 0 to 2 seem) to Ar:0₂(2:1) mixture enhances the (2 0 0) texturing, while the addition of N₂ gas (from 0 to 2 seem) to Ar ambient slightly weakens the (1 1 1) texturing. The deposition rate is reduced from 6.1 to 1.5 nm/min when o₂ gas is added to Ar ambient. The addition of N₂ gas to the Ar:o₂(2:1) mixture slightly increases the deposition rate from 1.8 to 2.6 nm/min, whereas adding N₂ gas to Ar only ambient somewhat reduces the rate from 6.1 to 4.4 nm/min. The carrier concentration of the films is increased and the mobility is decreased as the o₂ flow rate in the Ar:o₂mixture is increased. The addition of N₂ gas to the Ar:o₂ (2:1) mixture increases the resistivity of the films, while adding N₂ gas to Ar ambient decreases the resistivity. The transmittance and optical bandgap of the films are reduced (from 58.4 to 45.5% at 550 nm and from 3.5 to 3.3 eV, respectively) with increasing 0₂ flow to Ar ambient When N₂ gas is added to the Ar:o₂ (2:1) mixture, the transmittance in the visible wavelength range increases from 58.4 to 71.3% and the optical bandgap increases from 3.5 to 3.6 eV. However, adding N₂ gas to the Ar only ambient results in decrease in the transmittance in the visible wavelength region (from 69.3 to 56%) and the optical bandgap (from 3.7 to 3.5 eV).