Electrical and optical properties of chemically doped $p$-type MoS$_{2}$

Molybdenum disulfide is a model example of two-dimensional semiconductors, holding promise for applications in optoelectronic devices and field-effect transistors. So far, however, its practical use has been exclusively restricted to native, n-type doping. Here we experimentally demonstrate stable $p$-type conduction in molybdenum disulfide substitutionally doped with niobium. This chemical doping leads to a degenerate hole density of $\sim$ 1.8 $\times$ 10$^{14}$ cm$^{\mathrm{-2}}$ and enables gate-tunable van der Waals $p$-$n$ homo-junctions. Also, the $p$-type monolayer molybdenum disulfide exhibits a greatly enhanced and broadened photoluminescence compared to that acquired from undoped monolayers. Our study demonstrates the stable $p$-type doping in molybdenum disulfide, and also reveals an effective way to tailor optical and electrical properties of two-dimensional semiconductors with extrinsic dopants.