Improvement of the effective work function and transmittance of thick indium tin oxide/ultrathin ruthenium doped indium oxide bilayers as transparent conductive oxide

Abstract Ruthenium doped indium oxide (In 1 − x Ru x O y ) films fabricated using DC magnetron co-sputtering with In 2 O 3 and Ru targets were investigated for use as transparent conductive oxides. The In 1 − x Ru x O y films had an amorphous structure in the wide compositional range of x = 0.3–0.8 and had an extremely smooth surface. The transmittance and resistivity of the In 1 − x Ru x O y films increased as the Ru content increased. The transmittance of the In 0.38 Ru 0.62 O y film improved to over 80% when the film thickness was less than 5 nm, while the specific resistivity ( ρ ) was kept to a low value of 1.6 × 10 − 4  Ω cm. Based on these experimental data, we demonstrated that thick indium tin oxide (In 0.9 Sn 0.1 O y , ITO) (150 nm)/ultrathin In 0.38 Ru 0.62 O y (3 nm) bilayers have a high effective work function of 5.3 eV, transmittance of 86%, and low ρ of 9.2 × 10 − 5  Ω cm. This ITO/In 0.38 Ru 0.62 O y bilayer is a candidate for use as an anode for organic electroluminescent devices.