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

Abstract SnO 2 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 SnO 2 thin films deposited via RF magnetron sputtering. Three SnO 2 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 SnO 2 :In films exhibit parabolic trends with respect to annealing temperature with minima values at 300 °C, while that of UID-SnO 2 increases monotonically. P-type conductivity was found in the 300 °C-annealed SnO 2 :18.2 at% In films both in air and N 2 , with the N 2 -annealing leading to higher mobility (162.7 cm 2 ·V −1 ·s −1 ) and lower resistivity (0.57 Ω·cm). The Fermi levels of the SnO 2 :In films are found to locate deep inside the bandgap, which is beneficial to form homojunctions with SnO 2 of shallow Fermi levels.