Ultrafast and Highly Sensitive Dual-Channel FET Photodetector Based on a Two-Dimensional MoS₂ Homojunction

Two-dimensional transition metal dichalcogenide-based phototransistors have been intensively studied in recent years due to their high detection rate and flexibility. However, the photogating effect, usually appearing in the devices, leads to a poor transient photoresponse, which slows down the imaging rate of the camera based on the devices. Here, we demonstrate a dual-channel two-dimensional field-effect phototransistor composed of a vertical molybdenum disulfide (MoS₂) p-n homojunction as the sensitizing channel layer. Owing to the effective separation by the vertical built-in electric field and rapid migration of photoexcited electrons and holes in the separated channels, the fabricated dual-channel FET device simultaneously exhibits prominent responsivity and greatly improved time response in comparison to the pristine MoS₂ FET detectors. Excellent device performance has been achieved, with a responsivity of 3.4 × 10⁴ A/W at a source-drain voltage (V_DS) of 1 V, corresponding to a detectivity (D*) of 1.9 × 10¹³ Jones@532 nm and a gain of more than 10⁵ electrons per photon, an external quantum efficiency of 9.6%, and a response time of tens of milliseconds. Especially, the response time of the dual-channel FET device is 3 orders of magnitude faster than that of the pristine device. Our results provide a new way to overcome the inherent photogating drawback of two-dimensional FET optoelectronic devices and to develop a related high frame rate imaging system.