Realization of highly transparent and low resistance TiO₂/Ag/TiO₂ conducting electrode for optoelectronic devices

The effect of TiO₂ thickness on the optical and electrical properties of TiO₂/Ag/TiO₂ multilayer films deposited on glass substrates was investigated. The as-deposited TiO₂ samples were found to be amorphous. The transmission window became wider and gradually shifted toward lower energies as the TiO₂ thickness increased from 10 to 50 nm. In particular, the TiO₂/Ag/TiO₂ (40 nm/18.8 nm/40 nm) multilayer film exhibited a transmittance of ~ 95% at 550 nm. Incrementally increasing the TiO₂ thickness to 50 nm gradually decreased the carrier concentration to 6.1×10²¹ cm^-3, while the charge mobility varied from 22.3 to 20.4 cm² V^-1 s^-1. In addition, when increasing the TiO₂ thickness to 50 nm, the samples showed similar sheet resistances of 3.9-4.4 Ω/_□, but the resistivity increased by a factor of 3.8. Haacke's figure of merit (FOM) was calculated for the samples and plotted as a function of TiO₂ thickness; the TiO₂ (40 nm)/Ag (18.8 nm)/TiO₂ (40 nm) multilayer yielded the highest FOM of 159.9×10^-3 Ω^-1.