Anomalous Ultra‐Broadband Photoresponse Based on PdSe ₂ with Asymmetric Contact

Abstract Anomalous photoresponse with negative photoconductance (NPC) is rarely observed which is quite different from the common semiconductor with positive photoconductance (PPC) as the light can induce additional carriers. NPC effect is not widely studied because the performance of the NPC is limited and the device fabrication is uncontrollable. Here, a controllable way is reported to fabricate an anomalous photoresponse device through asymmetric metal contact with the PdSe ₂ . A mirror electrode‐enhanced vertical asymmetric contact (VAC) PdSe ₂ device is designed. The VAC PdSe ₂ device demonstrated the NPC effect in an ultra‐broadband spectral range from 637 nm to the long‐wave infrared (LWIR) 10.6 µm. Notably, the device exhibits excellent uncooled mid‐wave infrared (MWIR) and LWIR detection ability with a high photoresponsivity ( R ) of 128.4 AW ⁻¹ and 38.2 AW ⁻¹ , respectively. Furthermore, the lateral asymmetric contact (LAC) PdSe ₂ device is also investigated. The LAC PdSe ₂ device demonstrated competitive performance including high photovoltaic responsivity up to 0.22 AW ⁻¹ and external quantum efficiency (EQE) of 67.5%, fast photoresponse speed with rise time τ _r = 28.7 µs and decay time τ _d = 31.2 µs, and anisotropic dichroic ratio ( γ ) of ≈1.15. The results open a new platform for studying anomalous photoresponse with high performance in uncooled LWIR photodetection.