Accessing the transport properties of pristine few-layer black phosphorus by van der Waals passivation in inert atmosphere

TL;DR

This study demonstrates that passivating ultrathin black phosphorus with graphene or hexagonal boron nitride in an inert atmosphere preserves its intrinsic transport properties, preventing degradation and revealing its true electronic behavior.

Contribution

The paper introduces a passivation method using 2D materials to protect black phosphorus from air degradation, enabling accurate transport property measurements.

Findings

Passivation improves black phosphorus charge transport properties.

Oxygen acceptor states cause band structure perturbations in unpassivated samples.

Pristine passivated black phosphorus shows symmetric electron and hole conduction.

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.