Electrical and Optical Properties of Fluorine Doped Tin Oxide Thin Films Prepared by Magnetron Sputtering

TLDR

Depositing FTO by magnetron sputtering is an environmentally friendly technique that, using loosely packed blended powder targets, offers an efficient and low‑cost means of screening candidate compositions. The study investigates how the chemical composition of the SnO₂/SnF₂ target influences the structural, optical, and electrical properties of the resulting thin films. FTO coatings were fabricated by mid‑frequency pulsed DC closed‑field unbalanced magnetron sputtering from blended SnO₂/SnF₂ targets in an Ar/O₂ atmosphere, deposited as 400 nm films on glass without post‑deposition annealing. The optimized 12 % SnF₂/88 % SnO₂ target produced a polycrystalline tetragonal film with 83 % visible transmittance, a 3.80 eV band‑gap, 6.71 × 10⁻³ Ω·cm resistivity, 1.46 × 10²⁰ cm⁻³ carrier concentration, and 15 cm²/V·s mobility.

Abstract

Fluorine doped tin oxide (FTO) coatings have been prepared using the mid-frequency pulsed DC closed field unbalanced magnetron sputtering technique in an Ar/O2 atmosphere using blends of tin oxide and tin fluoride powder formed into targets. FTO coatings were deposited with a thickness of 400 nm on glass substrates. No post-deposition annealing treatments were carried out. The effects of the chemical composition on the structural (phase, grain size), optical (transmission, optical band-gap) and electrical (resistivity, charge carrier, mobility) properties of the thin films were investigated. Depositing FTO by magnetron sputtering is an environmentally friendly technique and the use of loosely packed blended powder targets gives an efficient means of screening candidate compositions, which also provides a low cost operation. The best film characteristics were achieved using a mass ratio of 12% SnF2 to 88% SnO2 in the target. The thin film produced was polycrystalline with a tetragonal crystal structure. The optimized conditions resulted in a thin film with average visible transmittance of 83% and optical band-gap of 3.80 eV, resistivity of 6.71 × 10−3 Ω·cm, a carrier concentration (Nd) of 1.46 × 1020 cm−3 and a mobility of 15 cm2/Vs.