GeAs as an emerging p-type van der Waals semiconductor and its application in p-n photodiodes.

van der Waals (vdW) layered materials have shown great potential for future optoelectronic applications owing to their unique and variable properties. In particular, two-dimensional layered materials enable the creation of various circuital building blocks via vertical stacking, e.g. the vertical p-n junction as a key one. While numerous stable n - type layered materials have been discovered, p - type materials remain relatively scarce. Here, we report on the study of multilayer germanium arsenide (GeAs), another emerging p - type vdW layered material. We first verify the efficient hole transport in a multilayer GeAs field-effect transistor with Pt electrodes, which establish low contact potential barriers. Subsequently, we demonstrate a p-n photodiode featuring a vertical heterojunction of a multilayer GeAs and n - type MoS 2 monolayer, exhibiting a photovoltaic response. This study promotes that 2D GeAs is a promising candidate for p - type material in vdW optoelectronic devices.