High-performance p-type field-effect transistors using substitutional doping and thickness control of two-dimensional materials

In silicon field-effect transistors (FETs), degenerate doping of the channel beneath the source and drain regions is used to create high-performance n- and p-type devices by reducing the contact resistance. Two-dimensional semiconductors have, in contrast, relied on metal-work-function engineering. This approach has led to the development of effective n-type 2D FETs due to the Fermi-level pinning occurring near the conduction band, but it is challenging with p-type FETs. Here we show that the degenerate p-type doping of molybdenum diselenide and tungsten diselenide-achieved through substitutional doping with vanadium, niobium and tantalum-can reduce the contact resistance to as low as 95 ohm mu m in multilayers. This, though, comes at the cost of poor electrostatic control, and we find that the doping effectiveness-and its impact on electrostatic control-is reduced in thinner layers due to strong quantum confinement effects. We, therefore, develop a high-performance p-type 2D molybdenum diselenide FET using a layer-by-layer thinning method to create a device with thin layers at the channel and thick doped layers at the contact regions. Substitutionally doped two-dimensional diselenides can be used to make p-type field-effect transistors with reduced contact resistance and good electrostatic control by varying the thickness of the channel and contact regions.