Characterization of Amorphous SnO₂:N Thin-films Prepared by RF Magnetron Sputtering in Ar/N₂ Mixed Gas Atmosphere

Abstract

Nitrogen (N) has attracted attention as a hole dopant for SnO_x semiconductors. We have previously reported p-type conversion of n-type SnO₂ thin films by N doping by thermal annealing in N₂ atmosphere. Since the diffusion length of N is several 10 nm order, uniform N doping in the film is limited in terms of practical applications. In this study, we investigated N doping into the bulk using RF magnetron sputtering in Ar/N₂ mixed gas atmosphere. N-doped SnO₂ (SnO₂:N) thin film was fabricated by the sputtering at a substrate temperature of 300°C and a N₂ concentration varied between 25 and 80%. The fabricated thin films were amorphous under all deposition conditions. As the N₂ concentration increased, the absorption edge shifted to the longer wavelength and optical bandgap became narrower. XPS and PL analyses showed that as oxygen vacancy decreased, Sn-N bonding and N^3- component, which acts as an acceptor, increased. Hall-effect measurement showed the SnO₂:N deposited at 80% N₂ concentration has p-type conduction. We believe that this is because increase in density of states of N 2p orbital. However, the mobility was 0.12 cm²/Vs, suggesting limitation in improvement of electrical properties even in N doping into the bulk.