Influence of Acceptor Defects on the Structural, Optical and Electrical Properties of Sputtered NiO Thin Films

Abstract

NiO thin films have many applications due to the versatility of their optical and electrical characteristics, which can be controlled by the deposition parameters and/or subsequent heating. To achieve proper control, understanding their behavior, it is necessary to establish the influence of acceptor defects on the electronic characteristics of the films in relation to the preparation procedure. For this purpose, polycrystalline NiO thin films are grown by reactive DC sputtering on unheated glass substrates, with different acceptor defects depending on the oxygen partial pressure in the sputtering gas mixture. Their structural, morphological, optical, and electrical properties are analyzed comparatively in the as‐grown conditions and after heating in air at 400 °C. The results indicate that nickel vacancies along with hole carriers are effectively increased in films prepared at high oxygen ratios, increasing the electrical conductivity and the optical absorption at low energies, while distorting the crystalline lattice and decreasing the mean crystallite size. The heat treatment improves the crystallinity, bringing the different samples toward an equilibrium state that equates their optical and electrical characteristics. The intrinsic equilibrium constant is in the order K i ≈ 1022 cm−6, whereas the hole effective mass is found dependent on the carrier concentration.