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 O-2 or N-2 gases affect the structural, electrical and optical properties of RF-magnetron-sputtered NiO films. It is shown that the addition of O-2 gas to Ar ambient (namely, Ar:O-2=2:1 to 1:2) slightly reduces the (2 0 0) texturing of the NiO films. The introduction of N-2 gas (from 0 to 2 sccm) to Ar:O-2 (2:1) mixture enhances the (2 0 0) texturing, while the addition of N-2 gas (from 0 to 2 sccm) to Ar ambient slightly weakens the (1 1 1) texturing. The deposition rate is reduced from 6.1 to 1.5 nm/min when O-2 gas is added to Ar ambient. The addition of N-2 gas to the Ar:O-2 (2:1) mixture slightly increases the deposition rate from 1.8 to 2.6 nm/min, whereas adding N-2 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 O-2 flow rate in the Ar:O-2 mixture is increased. The addition of N-2 gas to the Ar:O-2 (2:1) mixture increases the resistivity of the films, while adding N-2 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 O-2. flow to Ar ambient. When N-2 gas is added to the Ar:O-2 (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 N-2 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). (C) 2012 Elsevier Ltd. All rights reserved.