Dual-Gate Black Phosphorus Field-Effect Transistors with Hexagonal Boron Nitride as Dielectric and Passivation Layers

Two-dimensional black phosphorus (BP) has attracted much attention recently because of its applicability in high-performance electronic and optoelectronic devices. BP field-effect transistors (FETs) with a tunable band gap (0.3-1.5 eV) have demonstrated a high on-off current ratio and a high hole mobility with an ambipolar behavior in global-gated devices. However, local-gated BP FETs for integrated circuits have been reported with only p-type behaviors and a low on-current compared with global-gated BP FETs. Furthermore, BP, which is not stable in air, forms sharp spikes on its surface when exposed to humid air. This phenomenon plays a role in accelerating the degradation of the electrical properties of BP devices, which can occur even within a day. In this paper, we first demonstrate the origin of transport limitations of local-gated BP FETs by comparing the transport properties of hexagonal boron nitride (h-BN)-based device architectures with those of a bottom-gated BP FET on a Si/SiO₂ substrate. By using h-BN as passivation and dielectric layers, BP FETs with a low gate operating voltage were fabricated with two different transistor geometries: top-gated and bottom-gated FETs. The highest mobility extracted from the global-gated BP FETs was 249 cm² V^-1 s^-1 with a subthreshold swing of 848 mV dec^-1.