Surface charge transfer doping and effective passivation of black phosphorus field effect transistors

Abstract

Few-layer black phosphorus generally shows p-type or hole dominated ambipolar transfer characteristics with electron mobility being equal to or nearly zero, and tends to degenerate very quickly under ambient conditions. Herein, we demonstrate an effective surface charge transfer doping and passivation scheme on few-layer black phosphorus through in situ encapsulation by thin layer hexagonal boron nitride and surface modification by HfO₂ or MgO. Both HfO₂ and MgO can provide an electron doping effect on black phosphorus, resulting in an increase in electron mobility over one order of magnitude up to 65 cm² V⁻¹ s⁻¹ modified by HfO₂ and 305 cm² V⁻¹ s⁻¹ modified by MgO, respectively. The highest electron mobility achieved approaches the record value in the literature, and the hole mobility of the same sample is also as high as 1150 cm² V⁻¹ s⁻¹. Thin layer hexagonal boron nitride not only isolates black phosphorus from ambient conditions, but also protects it from destruction by metal oxides' deposition. Our work provides an effective technique to simultaneously realize electron doping and passivation on black phosphorus field effect transistors.