Near-infrared photosensors based on uniform 2D carbon nanotube networks

Semiconducting single-walled carbon nanotubes (s-SWCNTs) offer extraordinary optical and electronic properties, including diameter-dependent band gaps and strong near-infrared (NIR) absorption, positioning them as promising candidates for developing advanced optoelectronic devices. However, the potential of fabricating high-quality CNT networks and their applications in photo-sensing is not fully investigated. In this work, we demonstrate the fabrication and characterization of high performance, near-infrared photosensors based on two-dimensional s-SWCNT networks. Three solution-based deposition methods, drop-casting, spin-coating, and dip-coating are explored, with the dip-coating process emerging as the most effective one for forming uniform, well-connected nanotube networks. The network morphology is characterized by SEM, AFM, and EDS, while the material purity and structure are validated using optical absorption, Raman spectroscopy, XRD, and XPS. A planar CNT/Si photosensor architecture is fabricated using gold electrodes and an n-doped silicon substrate. Under laser illumination at various wavelengths (405–980 nm), the device exhibits symmetric I-V behaviour and high photo response at 980 nm, corresponding to the S₂₂ excitonic transition of the CNTs. The photosensor shows rapid rise/decay times and peak responsivity of 12 mA/W. Energy band diagram modeling supports the observed bias-symmetric conduction and confirms the role of the CNT network in enabling efficient charge transport and photon–carrier conversion.