Room-Temperature Phototransistor with Negative Photoresponsivity of 10⁸ A W⁻¹ Using Fullerene-Sensitized Aligned Carbon Nanotubes

Detection of low intensity light down to a few photons requires photodetectors with high gain. A new photodetector is reported based on C₆₀-sensitized aligned carbon nanotube (CNT) transistors with an extremely high responsivity of 10⁸ A W⁻¹ (gain > 10⁸) in the ultraviolet and visible range, and 720 A W⁻¹ (gain = 940) in the infrared range. In contrast to most sensitized phototransistors that operate on the photogating effect, the new photodetector operates on the modulation of the electrons scattering in the CNTs, leading to negative photoconductivity. Comparison with similar photodetectors using random CNT networks shows the benefit of using aligned CNTs. At room temperature, the aligned CNT photodetectors are demonstrated to detect a few tens of photons per CNT.