Semiconductor–Semimetal Transition‐Driven Photocurrent Spurt and Infrared Band Response in Lead Iodide at High Pressure

Abstract Topological semimetals have attracted flourishing interest as promising candidates for their unique advantages in achieving highly sensitive, low‐energy photodetection with ultrafast operation. Although various semimetals have been explored recently, new semimetals are still being pursued for high‐responsivity photodetectors with broadband response. Here, a pressure‐induced semiconductor–semimetal transition is observed in two‐dimensional wide‐band semiconducting lead iodide (PbI₂). The photocurrent under visible light shows abrupt increases by two orders of magnitude at ≈25 GPa, where the crystalline structure transforms from the Pnma to I4/MMM phase. Meanwhile, the responding band expands from visible light to at least the telecom wavelength 1550 nm. The high‐pressure absorption spectra of PbI₂ suggest that the electrical band is closed at the transition point, while the charge transport shows that the sample is still not metallic. Through first‐principles calculations, the photocurrent spurt and infrared band response are attributed to the appearance of a semimetal phase at high pressure, which well explains the nonmetallic transport. The prominent drop in lifetime to a few picoseconds in ultrafast spectroscopy under pressure further confirms the semiconductor–semimetal transition in PbI₂. Pressure‐induced semimetallization opens a new strategy for designing a high‐performance photodetector with broadband response.