Multilayer 2D germanium phosphide (GeP) infrared phototransistor.

Layered two-dimensional (2D) materials with broadband photodetection capability have tremendous potential in the design and engineering of future optoelectronics devices. To date, studies of 2D semiconductors are actively focused on graphene, black phosphorus, and black arsenic phosphorus as attractive candidates. So far, however, novel group IV-V 2D semiconductors (e.g., GeAs and SiAs) have not been extensively explored for broad-band optoelectronics applications. Here, we report a high-performance multilayered 2D GeP gate-tunable photodetector that operates at a short-wavelength infrared (SWIR) regime. With a back-gate device geometry, a p-type behavior is observed at room temperature. Furthermore, a broadband spectral response from UV to optical communication wavelengths is detected. Under a nanowatt-level illumination, a peak responsivity of 25.5 A/W at λ = 1310 nm is achieved with detectivity of ∼ 1×1011 cm.Hz1/2.W-1 at a source-drain bias of -5 V and medium gate voltage bias of -30 V. Additionally, the devices show a relatively low dark current of 40-250 nA for device area in the range of 50-600 µm2 and excellent stability and reproducibility. Our work demonstrates the potential of 2D GeP as an alternative mid-infrared material with broad optical tunability suitable for optical communication and low-light-level detection applications.