  Novel group IVV 2D semiconductors (e.g., GeAs and SiAs) has arisen as an
attractive candidate for broad-band photodetection and optoelectronic
applications. This 2D family has wide tunable bandgap, excellent thermodynamic
stability, and strong in-plane anisotropy. However, their photonic and
optoelectronic properties have not been extensively explored so far. In this
work we demonstrate a broadband back-to-back metal-semiconductor-metal (MSM)
Schottky photodiode with asymmetric contact geometries based on multilayered 2D
GeAs. The photodetector exhibited a Schottky barrier height (SBH) in the range
of 0.40 to 0.49 eV. Additionally, it showed low dark current of 1.8 nA with
stable, reproducible, and excellent broadband spectral response from UV to
optical communication wavelengths. The highest measured responsivity in the
visible is 905 A/W at 660 nm wavelength and 98 A/W for 1064 nm near infrared.
Most notably, the planner configuration of this GeAs photodetector showed low
detector capacitance below 1.2 pf, low voltage operation (<1V), and a large
bandwidth which may exceed 40 GHz. The stability and broadband response of the
device are promising for this 2D materials application in high-speed
optoelectronic devices.
