Enhanced Low-Temperature SWIR Sensing Using 1600 nm PbS Quantum Dots Thin-Film Phototransistors: A Comparison with 940 nm Devices

This paper proposes a gap-type metal-semiconductor-metal (MSM) phototransistor architecture based on lead sulfide quantum dots (PbS QDs) for room-temperature infrared (IR) thermal sensing applications. Owing to their tunable bandgap, strong IR absorption, and simple fabrication, PbS QDs are promising candidates for low-cost photodetection. The devices with PbS QDs exhibiting peak absorptions at 940 and 1600 nm were fabricated and compared. The 1600 nm device demonstrated a lower detectable temperature threshold and a linear photocurrent–temperature response above 150 °C, whereas the 940 nm device required over 300 °C. The enhanced performance of the 1600 nm device arises from its narrower bandgap, enabling stronger IR absorption and higher responsivity. However, the larger QD size and higher defect density result in a slower total response time (13.21 s) compared with the 940 nm device (157 μs). Consequently, the 940 nm device is suitable for real-time monitoring of high-temperature objects, while the 1600 nm device is preferable for static or slowly varying thermal radiation. These findings highlight the potential of PbS QD–based gap-type MSM photodetectors to achieve extended room-temperature IR sensing without external cooling, providing a feasible approach for low-cost and uncooled thermal imaging applications.