Monolayer black phosphorus and germanium arsenide transistors via van der Waals channel thinning

Two-dimensional (2D) semiconductors can potentially be used to create scaled electronic devices. However, for a number of promising 2D materials—such as black phosphorus and germanium arsenide—the fabrication of monolayer transistors is challenging and is limited by the difficulties in forming robust electrical contacts with the delicate 2D materials. Here, we report the fabrication of monolayer black phosphorus and germanium arsenide transistors with three-dimensional raised contacts using a van der Waals peeling technique. Through layer-by-layer mechanical peeling, the channel region of a multilayer black phosphorus transistor can be gradually reduced to monolayer thickness without degrading its delicate lattice and while retaining a multilayer contact region. Using the technique, we measure the electrical properties of the same 2D transistor with different channel thicknesses. We find that the carrier mobility of black phosphorus drops sharply when reducing body thickness, behaving more like a conventional bulk semiconductor rather than a pure van der Waals semiconductor.