Ultrasensitive negative photoresponse in 2D CrGeTe photodetector with light-induced carrier trapping.

CrGeTe, a layered ferromagnetic semiconductor, has triggered extensive research interest due to its fantastic ferromagnetism and semiconducting characteristics as well as potential applications in next-generation spintronic and nanoelectronic devices. On the basis of its ferromagnetism, combined with rich electronic and optical properties, CrGeTe could be a promising candidate for optoelectronics including magnetophotonics and photodetectors. However, there are no relevant studies addressing this to date. In this work, we comprehensively investigated the photoresponse characteristics of few-layer CrGeTe-based detectors. An uncommon negative photoconductivity (NPC) and correlated mechanism are explored with the CrGeTe photodetector. It is found that, both NPC and positive photoconductivity (PPC) may exist in an individual CrGeTe device, which are adjustable by control of the incident light intensity. More significantly, the NPC behavior enables ultrasensitive photoresponses of the CrGeTe photodetectors, where the detection of a weak light with an incident power intensity as low as 0.04 pW and a high responsivity of 340 AW is achieved. This extraordinary performance demonstrates that the two-dimensional (2D) CrGeTe holds great promise for applications in ultraweak light detection.