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 MoS2 monolayer, exhibiting a photovoltaic response. This study promotes that 2D GeAs is a promising candidate for p-type material in vdW optoelectronic devices.