关键词: infrared-transparent conductor, indium tin oxide, ultra-thin Cu capping layer, oxygen vacancy

Abstract: Infrared-transparent conductors have attracted considerable attention due to their potential applications in electromagnetic shielding, infrared sensors, and photovoltaic devices. However, most known materials face the critical challenge of balancing high infrared transmittance with high electrical conductivity across the broad infrared spectral band (2.5-25 μm). While ultra-thin indium tin oxide (ITO) films have been demonstrated to exhibit superior infrared transmittance, their inherent low electrical conductivity necessitates additional enhancement strategies. This study systematically investigates the effects of oxygen vacancy concentration regulation and ultra-thin copper capping layer integration on the infrared optoelectronic properties of 20 nm-thick ITO films. A fundamental trade-off is revealed in ITO films that increased oxygen vacancy content enhances the electrical conductivity while compromising the infrared transmittance. Meanwhile, following the introduction of a Cu capping layer, the Cu/ITO system exhibits opposing dependencies of infrared transmittance and electrical conductivity on the capping layer thickness, with an optimum thickness of $\sim 3$ nm. Finally, by constructing a Cu (3 nm)/ITO (20 nm) heterostructure with varying oxygen vacancy content, we demonstrate the combined effect of the ultra-thin Cu capping layer and moderate oxygen vacancy content on optimizing the carrier transport network. This configuration simultaneously minimizes surface/interfacial reflection and absorption losses, achieving high infrared transmittance (0.861) and a low sheet resistance of 400 $\Omega $/sq. Our findings highlight the critical role of the combined effect of metal/oxide heterostructure design and defect engineering in optimizing infrared-transparent conductive properties.

Key words: infrared-transparent conductor, indium tin oxide, ultra-thin Cu capping layer, oxygen vacancy