Structural, electrical and optical properties of samarium fluoride doped SnO2 transparent conducting oxide thin films for optoelectronic device applications

Abstract

In this study, p-type transparent tin oxide (SnO₂) based semiconductor thin films were deposited onto glass substrates by sol-gel dip-coating method using samarium-trifluoride (SmF₃) as acceptor dopant. The films were prepared by co-doping 2 mol.% of SmF₃ into SnO₂ (SFTO), followed by annealing temperature at 475 ^°C. XRD analysis results showed that the films exhibited the tetragonal rutile SnO₂ phase. The p-type conductance of the SFTO films were confimed by Hall effect and Seebeck coefficient measurements. Resistivity and mobility of the SmF₃ doped SnO₂ film is 7.83 × 10^–3Wcm and 7.57 cm² V^–1 s^–1, respectively, which reduce in comparing with those of un-doped SnO₂ film. Carrier concentration is large increase from –9.34 ´ 10¹⁸ cm^–3 for un-doped- to +1.05 × 10²⁰ cm^–3  for SmF₃ doped-SnO₂ film. The p-type SFTO film showed a high transmittance of 74.3% at 550 nm, with band gap energy of 3.63 eV. Furthermore, a transparent p-SnO₂:SmF₃/n-ZnO:Al (Al doping level of 2 mol.%) heterojunction was fabricated on alkali-free glass substrates. The I-V curve measurement for the p-n heterojunction diode showed a typical rectifying characteristic with a forward turn-on voltage of 1.55 V. With obtained properties, the p-type SFTO film holds great promise for optoelectronic devices applications.