Impact of In-doping and post-annealing on the properties of SnO2 thin films deposited by magnetron sputtering

Abstract

SnO2 is a transparent semiconductor that has shown versatile applications in various fields. This study investigates the impact of In-incorporation and post-annealing on the structural, optical and electronical properties of SnO2 thin films deposited via RF magnetron sputtering. Three SnO2 target compositions were employed, with one unintentionally doped (UID), one with 1.0 at% In, and the other with 18.2 at% In. UV–vis spectroscopy reveals the presence of band tails in the as-deposited films, which can be significantly suppressed through annealing, particularly in air. Oxygen vacancy-related defect states below the conduction band minimum are believed to be responsible. Further, film thicknesses, refractive indices, and absorption coefficients were estimated from the UV–vis spectra of the films, employing the irritative Swanepoel method. The resistivities of SnO2:In films exhibit parabolic trends with respect to annealing temperature with minima values at 300 °C, while that of UID-SnO2 increases monotonically. P-type conductivity was found in the 300 °C-annealed SnO2:18.2 at% In films both in air and N2, with the N2-annealing leading to higher mobility (162.7 cm2·V−1·s−1) and lower resistivity (0.57 Ω·cm). The Fermi levels of the SnO2:In films are found to locate deep inside the bandgap, which is beneficial to form homojunctions with SnO2 of shallow Fermi levels.