Effects of Oxygen Partial Pressure on the Properties of SnOx Thin Films Doped with Indium

This study examined the effects of the oxygen partial pressure on the properties of heavily indium-doped tin-oxide (In-SnOx) thin films grown at room temperature by reactive direct-current pulse sputtering from a mixed metallic target containing Sn (70 atomic %)-In (30 atomic %). X-ray photoelectron spectroscopy (XPS), dynamic secondary-ion mass spectrometry, X-ray diffraction (XRD), and Hall Effect measurements showed that the In-SnOx samples prepared with oxygen pressures of 10–20% had metallic properties. This was attributed to the notable Sn0 area ranges of 5.6–17.3%, low resistivity ranges of 5.5×10−3–2×10−4 Ωcm, and the high carrier concentration ranges of 3.5×1021–5.1×1022/cm3. On the other hand, the Sn4+ area and the resistivity increased significantly to 73.3% and 9.4 Ωcm. In comparison, the Sn2+ area and the electron concentration decreased dramatically to 23.6% and 6.5×1016/cm3, respectively, with increasing oxygen partial pressure up to 30%. The samples prepared with oxygen pressures higher than 20% exhibited nonmetallic properties with the dominant n-type SnO2 phase. This steep increase in the Sn4+ area was attributed to an increase in the oxygen contents in the samples, resulting in a decrease in the number of oxygen vacancy donors in the samples prepared with oxygen pressures higher than 20%. The decrease in the Sn2+ area was related to a decrease in the indium (In) contents in the samples, which also decreased the number of metal acceptors in the samples. XRD also showed that the metallic indium stannide (In0.2Sn0.8) and In–Sn–O(ITO) peaks coexisted for samples prepared with an oxygen pressure of 0–10%. In contrast, the samples prepared with oxygen pressures higher than 20% had an amorphous structure with SnO2 and SnO phases, supporting the XPS and Hall Effect measurement results.