Modulation of the conductive behavior of NiO thin film deposited by HiPIMS through varying the O2 flow ratio

Abstract

Nickel oxide (NiO) films were prepared through High Power Impulse Magnetron Sputtering (HiPIMS). The influence of O2/(Ar + O2) flow ratio (oxygen flow ratio) from 0.5% to 3% on structural and optoelectronic qualities of NiO films were studied. The results indicate that deposition rate of NiO film reduces as increase of oxygen flow ratio. Atomic force microscopy shows that as oxygen flow ratio increases, surface roughness of NiO films decrease. The transmittances of the NiO films are over 60% in the visible wavelengths. Hall effect measurements suggested that by adjusting the oxygen flow ratio NiO films with different type of conduction can be obtained. The carrier concentration of NiO films increase significantly as oxygen flow ratio goes up, which is caused by the fact that more nickel vacancies and interstitial oxygen are formed in NiO films. Therefore, the electrical conductivity enhances accordingly. The XPS analysis demonstrates the presence of both Ni2+ and Ni3+ oxidation states and also confirms the transition of conductive type of the NiO films. HiPIMS is a potential approach for depositing n type or p type transparent conductive oxide NiO films.