Influence of O2/Ar flow ratio on the structure, optical and electrical properties of DC reactively magnetron-sputtered face-centered cubic NiO films at room temperature

Abstract

Single-phase NiO films with high carrier mobility and low electrical resistivity are crucial for NiO-based heterojunction solar cells. Herein, a series of face-centered cubic (fcc) nickel oxide (NiO) films was room-temperature prepared at different O2/Ar flow ratio (Roa) values through low-cost DC reactive magnetron sputtering. With increase of Roa, the film crystallization is initially improved, and the film's free carrier concentration increases, thereby resulting in a slight blue shift in optical absorption edge. The oxygen-rich state in the form of nickel vacancies and interstitial oxygen enlarges the film's lattice distortion and thus leads to a red shift in optical absorption edge. The reduced film transmittance with increase of Roa is due to the enhanced point defect scattering. The free carrier concentration of the films reaches the maxima of 3.17 × 1019/cm3 at 3:1 Roa and the hole mobility reaches the maxima of 1.53 cm2/Vs at 2:1 Roa.