Tuning Carrier Type and Density in Highly Conductive and Infrared-Transparent (Bi _{1– x} Sb _x ) ₂ Te ₃ Films

Infrared-transparent conductors have long been sought due to their broad optoelectronic applications in the infrared wavelength range. However, the search for ideal materials has been limited by the inherent trade-off between electrical conductance and optical transmittance. Band engineering offers an effective approach to modulate carrier type and density, enabling concurrent tuning of both the conductance and transmittance. In this work, we present a band engineering strategy that enables effective tuning of both infrared transmittance and electrical conductance in topological insulator (Bi 1– x Sb x ) 2 Te 3, bridging the gap and paving the way for applying topological insulators to infrared photoelectric devices. More importantly, with the combination of high carrier mobility and a large optical dielectric constant as suggested by the previous report, Sb 2 Te 3 achieves a high electrical conductance (∼1000 S/cm) and outstanding infrared transmittance (92.3%) in the wavelength range of 8–13 μm, demonstrating strong potential as an infrared-transparent conductor. Our findings reveal that concurrent enhancement of both carrier mobility and optical dielectric constant is key to overcoming the conductance–transmittance trade-off. This work provides valuable insight for the exploration of high-performance infrared-transparent conducting materials.