Solution-processed, ultrasensitive, high current density vertical phototransistor using porous carbon nanotube electrode

Abstract

Multi-wall carbon nanotube (MWCNT) thin film has been identified as the ideal electrode material due to their inherent electronic and optoelectronic properties. We have successfully fabricated a vertical field-effect phototransistor (vFEpT) using MWCNT as a porous source electrode. The optimized MWCNT electrodes showed an electrical conductivity of 3.92 × 103 S/m and a sheet resistance of about 490 Ω/□, with a layer thickness of about 520 nm. The as-fabricated transistor has p-type conductivity because of the unintentional doping of the PbS layer and the intrinsic hole transport property of the MWCNT network. Additionally, the device shows excellent photoelectric performance at 30 mWcm−2 of illumination, with a high current density of 2.3 × 10−3 Acm−2. With a high conductivity network for carrier transfer and separation, the special characteristics of MWCNT nanoporous thin film enable improved photoelectric properties, such as a high photoresponsivity of 3.16 AW−1 and a specific detectivity of 2.33 × 1012 Jones when illuminated at 808 nm light irradiance with an intensity of 0.6 µW/cm2. Furthermore, the device demonstrated a steady dynamic response to an optical signal, with rising and falling times of 31.8 ms and 32.9 ms, respectively. This work presents a new method for creating high-performance vertical phototransistors with MWCNT as the source electrode.