All matter above absolute zero temperature, including our bodies and planets light years away, emits thermal infrared radiation. Thus, infrared detection plays a large role in the modern world, as can be seen in thermal imaging, wireless control, and observational astronomy. The infrared wavelength range may be divided into near-infrared (NIR, 0.7–1 μm), short-wave infrared (SWIR, 1–3 μm), mid-wave infrared (MWIR, 3–5 μm), long-wave infrared (LWIR, 7–14 μm), and very-long-wave infrared (VLWIR, 12–30 μm) regions. Human body thermal radiation is centered around 9.5 μm, thus LWIR is of high interest for applications such as night-vision detection of humans. Researchers are currently searching through the class of two-dimensional (2D) materials for a LWIR-absorbing material. 2D materials, which have demonstrated excellent electrical and optical properties, offer a low-profile, potentially high-performance solution for night-vision detection. Platinum diselenide (PtSe2) is currently the only 2D material experimentally reported in literature to absorb up to LWIR. However, the responsivity of PtSe2 photoconductors suffers greatly at LWIR wavelengths.

This technical report presents electrical and optical characterization of three 2D materials: palladium diselenide (PdSe2), tellurium (Te), and platinum/sulfur/selenium (PtS(2-x)Se(x)x) alloys. Just recently, researchers have claimed PdSe2 to be a LWIR material, however we show through rigorous optical and electrical characterization that PdSe2 is instead a SWIR material. Solution-synthesized Te is introduced as a high-performance SWIR material. Lastly, we show progress on PtS(2-x)Se(x) alloys, which surpasses PtSe2 in terms of responsivity at LWIR wavelengths.




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