A broad spectral response is highly desirable for radiation detection in modern optoelectronics; however, it still remains a great challenge. Herein, we report a novel ultrabroadband photodetector based on a high-quality tin monoselenide (SnSe) thin film, which is even capable of detecting photons with energies far below its optical band gap. The wafer-size SnSe ultrathin films are epitaxially grown on sodium chloride via the 45° in-plane rotation by employing a sputtering method. The photodetector delivers sensitive detection to ultraviolet-visible-near infrared (UV-Vis-NIR) lights in the photoconductive mode and shows an anomalous response to long-wavelength infrared at room temperature. Under the mid-infrared light of 10.6 μm, the fabricated photodetector exhibits a large photoresponsivity of 0.16 A W-1 with a fast response rate, which is ∼3 orders of magnitude higher than other results. The thermally induced carriers from the photobolometric effect are responsible for the sub-bandgap response. This mechanism is confirmed by a temperature coefficient of resistance of -2.3 to 4.4% K-1 in the film, which is comparable to that of the commercial bolometric detectors. Additionally, the flexible device transferred onto polymer templates further displays high mechanical durability and stability over 200 bending cycles, indicating great potential toward developing wearable optoelectronic devices.
Keywords: SnSe film; flexible infrared photodetector; photobolometric effect; two dimensional structure; ultrabroad spectral response.