Transport properties of pristine few-layer black phosphorus by van der Waals passivation in an inert atmosphere

TLDR

Ultrathin black phosphorus (phosphorene) is a two‑dimensional semiconductor with a sizable band gap and promising electronic properties, but it rapidly degrades when exposed to ambient air. The study aims to develop a passivation strategy to preserve phosphorene’s intrinsic transport properties and to elucidate how oxidation alters its behavior. Atomically thin graphene or hexagonal boron nitride layers were employed as passivation coatings for ultrathin black phosphorus in an inert atmosphere. Channels passivated in inert gas without prior air exposure exhibited markedly improved n‑type transport and symmetric electron‑hole trans‑conductance, attributed to the absence of oxygen acceptor states that otherwise perturb the band structure.

Abstract

Ultrathin black phosphorus, or phosphorene, is the second known elementary two-dimensional material that can be exfoliated from a bulk van der Waals crystal. Unlike graphene it is a semiconductor with a sizeable band gap and its excellent electronic properties make it attractive for applications in transistor, logic, and optoelectronic devices. However, it is also the first widely investigated two dimensional electronic material to undergo degradation upon exposure to ambient air. Therefore a passivation method is required to study the intrinsic material properties, understand how oxidation affects the physical transport properties and to enable future application of phosphorene. Here we demonstrate that atomically thin graphene and hexagonal boron nitride crystals can be used for passivation of ultrathin black phosphorus. We report that few-layer pristine black phosphorus channels passivated in an inert gas environment, without any prior exposure to air, exhibit greatly improved n-type charge transport resulting in symmetric electron and hole trans-conductance characteristics. We attribute these results to the formation of oxygen acceptor states in air-exposed samples which drastically perturb the band structure in comparison to the pristine passivated black phosphorus.