Effects of Oxygen Ratio on the Properties of Tin Oxide Thin Films Doped with Bismuth

This study examins the effects of the oxygen ratio on the properties of bismuth (Bi)-doped tin oxide (Bi-SnOx) films deposited by radio frequency magnetron sputtering using a SnO (90at%)-Bi (10at%) ceramic target. The properties of the samples are characterized by X-ray photoelectron spectroscopy (XPS), Hall effect measurements, dynamic-secondary ion mass spectrometry (D-SIMS), and X-ray diffraction (XRD). The samples deposited without oxygen gas exhibit Sn4+ and Sn2+ XPS peak areas of 44.7 and 41.1%, respectively. The Sn4+ area increases to 64.1% with increasing oxygen ratio up to 20% with a concomitant decrease of the Sn2+ area to 26%, indicating that SnO2 with n-type conductivity is the dominant phase under a higher oxygen partial pressure. XPS shows that with increasing oxygen ratio, the chemical state of Bi changes from metallic Bi (Bi-0) to Bi3+. Furthermore, with increasing oxygen ratio, the Bi content in the samples increases because of the increase in Bi2O3 formation, which causes a decrease in the number of oxygen vacancies in the samples. These results suggest that the oxygen ratio is useful for controlling Bi doping in SnOx films. Therefore, Bi doping is valuable for suppressing the formation of oxygen vacancies and improving the properties of SnOx films.