Ultralow Dark Current and High‐Detectivity Infrared Phototransistors Enabled by Small‐Diameter Semiconducting Carbon Nanotubes

Abstract Due to their internal gain mechanism, emerging nanomaterial‐based infrared phototransistors show significant promise for highly sensitive detection; however, they usually suffer from high dark current (I_dark) and thus high noise, which restricts the actual detection capability of the detector. Here, a semiconducting carbon nanotube (CNT) film‐based phototransistor is proposed with an ultralow I_dark and a high response through the adoption of stacked ZnO/PbS colloidal quantum dot heterojunctions as the photogate to absorb the infrared photons and generate a photovoltage. Solution‐derived semiconducting CNTs with diameters ranging from 0.8 to 1.1 nm are utilized to create a network film that serves as the active channel of the transistor and provides an off‐state current as low as ≈50 fA; this enables an ultralow dark current (pA level) in the infrared phototransistor. By tuning the back‐gate bias, the synergistic modulation is demonstrated of the sensor response and electronic noise and achieve a high detectivity of 5.7 × 10¹³ Jones under an incident power density of 0.81 nW cm⁻² and 1300 nm infrared radiation. These findings provide a promising approach for attaining weak light infrared detection based on nanomaterial‐based photodetectors.