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

Abstract

We investigated how mixtures of Ar and O2 or N2 gases affect the structural, electrical and optical properties of RF-magnetron-sputtered NiO films. It is shown that the addition of O2 gas to Ar ambient (namely, Ar:O2=2:1 to 1:2) slightly reduces the (200) texturing of the NiO films. The introduction of N2 gas (from 0 to 2sccm) to Ar:O2 (2:1) mixture enhances the (200) texturing, while the addition of N2 gas (from 0 to 2sccm) to Ar ambient slightly weakens the (111) texturing. The deposition rate is reduced from 6.1 to 1.5nm/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 2.6nm/min, whereas adding N2 gas to Ar only ambient somewhat reduces the rate from 6.1 to 4.4nm/min. The carrier concentration of the films is increased and the mobility is decreased as the O2 flow rate in the Ar:O2 mixture 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 550nm and from 3.5 to 3.3eV, respectively) with increasing O2 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 3.6eV. 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 3.5eV).