N-type doping of black phosphorus by using benzyl viologen.

Black phosphorus (BP) meets several critical material requirements for the development of future nanoelectronic applications, but the realization of n-type semiconductor behavior form it has remained elusive. Here, we report the ambipolar characteristics of few-layer BP, induced using an novel technique: chemical doping with benzyl viologen (BV), which serves as a surface charge transfer donor for BP flakes. The n-doped BP devices exhibit excellent electron mobility up to \textasciitilde 83 cm$^{\mathrm{2}}$V$^{\mathrm{-1}}$s$^{\mathrm{-1}}$ from 2-terminal measurement at 300K, thereby demonstrating n-type behavior. On the basis of ambipolar BP devices, we also comprehensively analyzes temperature and BP thickness dependence of ambipolar devices, in which we found the degenerate doping limit below around 150K and highest electron transport performance in \textasciitilde 10 nm BP flakes at 300K. As a proof of concept, ultrafast BP photodetectors were fabricated with a very high photoresponsivity of \textasciitilde 10$^{\mathrm{4}}$ mA/W over the UV, visible, and IR spectral ranges. Furthermore, we fabricated a homogeneous BP based inverter through BV doping and h-BN capping that offers a feasible approach to fabricating a key building block of future 2D logic semiconductors.