Optical and electrical properties of NiO for possible dielectric applications

Abstract

Nickel oxide (NiO) is a versatile wide band gap semiconductor material. At present, transparent conducting oxide films find application as transparent electrodes and window coatings for opto-electronic devices but most are n-type. However p-type conducting films, of which NiO is one, are required as optical windows for devices where minority carrier injection is required. In this study, nickel (Ni) was resistively deposited on glass substrates and oxidised (isochronally) in oxygen at temperatures ranging from 300 ºC to 600 ºC. The oxidised Ni layers were subsequently characterised using scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-visible photospectrometry in the range 200 nm - 1000 nm. The four point probe method (van der Pauw geometry) was used to determine the sheet resistances of the oxidised films. SEM results of the surface revealed a strong dependence of the surface texture and particle size on the oxidation temperature and time. XRD performed on the oxidised Ni indicated progressive transformation from nanograined polycrystalline Ni to NiO at elevated temperatures. Film thicknesses, particle sizes, energy band gap and wavelength-dependent refractive indices were determined from transmission and absorbance data.