Oxygen Concentration Dependence of the Optical and Electrical Properties of Mn-Doped Tin Oxide Thin Films Deposited on a Polyethylene Terephthalate Substrate.

Mn (2.59 wt.%)-doped tin oxide (MTO) was deposited on a polyethylene terephthalate (PET) substrate using RF magnetron sputtering at room temperature. Oxygen was introduced during the sputtering process to prevent the reduction of transmittance and the formation of nonstoichiometric compositions. The dependence of the optical and electrical properties of MTO thin films on the O₂/(Ar+O₂) ratio was systematically investigated. The transmittance of the MTO single layer (24 nm) at 550 nm gradually increased from 85.9% to 88.2% with an increase of the O₂/(Ar+O₂) ratio from 0% to 7.9%. The optical band gap was also affected by the O₂/(Ar+O₂) ratio, varying from 3.30 to 3.64 eV. The MTO film deposited at an O₂/(Ar+O₂) ratio of 2.7% showed the minimum resistivity (0.03 Ω·cm). The XPS spectra indicated that the SnO₂ thin films become almost stoichiometric as the O₂/(Ar+O₂) ratio increased. Thus, this sputtering process can be used to prepare flexible MTO films with a wider optical band gap, improved transmittance, and decreased resistivity.