Measurement-based optimization and analysis of α-IGZO/Ag/α-IGZO transparent conducting electrodes fabricated using DC magnetron sputter deposition

Abstract

Transparent conducting electrodes have been systematically developed for optoelectronic devices and applications in industry through materials exploration and manufacturing process optimization. The nanostructural, optical and electrical properties were correlated with the embedded Ag interlayer thickness for the first time, for α-IGZO/Ag/α-IGZO trilayer electrodes fabricated using DC magnetron sputter deposition. Optimizing the Ag interlayer thickness at 14 nm achieves a maximum Haacke figure of merit (FOM) of 7.3 × 10−3 Ω−1, at least two orders of magnitude greater than that of the single IGZO film, with X-ray diffraction patterns indicating a crystalline phase that is also retained for thicker layers. Electrical and surface topography measurements confirm a uniform, continuous Ag interlayer film with bulk metallic behavior and resistivity as low as 6 × 10−5 Ω cm. Experimentally-calibrated finite-element modeling and ray tracing simulations unravel in the multilayer films, backscattering and transmission effects from random surface roughness, as well as phonon- or ionized impurity-scattering mediated free carrier absorption plus surface/interface scattering and interference effects. Moreover, film thickness-sensitive tuning of the optical bandgap between 2.98 and 3.14 eV was demonstrated, yielding a maximum bandgap and Haacke FOM at the optimized Ag interlayer thickness, and with many-body interactions outcompeting the Burstein-Moss effect above this thickness.