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

Ruthenium doped indium oxide (In1 − xRuxOy) films fabricated using DC magnetron co-sputtering with In2O3 and Ru targets were investigated for use as transparent conductive oxides. The In1 − xRuxOy 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 In1 − xRuxOy films increased as the Ru content increased. The transmittance of the In0.38Ru0.62Oy 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 (In0.9Sn0.1Oy, ITO) (150 nm)/ultrathin In0.38Ru0.62Oy (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/In0.38Ru0.62Oy bilayer is a candidate for use as an anode for organic electroluminescent devices.