Probing Out-of-Plane Charge Transport in Black Phosphorus with Graphene-Contacted Vertical Field-Effect Transistors

TL;DR

This study introduces a vertical graphene/BP heterostructure FET revealing out-of-plane charge transport mechanisms, with high current densities and distinct temperature-dependent conduction regimes, advancing understanding of BP-based devices.

Contribution

It presents a novel vertical device architecture for BP, identifying out-of-plane transport mechanisms and their dependence on temperature and gate voltage.

Findings

High on-state current densities (>1600 A/cm2)

Current on/off ratios exceeding 800 at low temperature

Identification of Schottky barrier and tunneling as dominant transport mechanisms

Abstract

Black phosphorus (BP) has recently emerged as a promising narrow band gap layered semiconductor with optoelectronic properties that bridge the gap between semi-metallic graphene and wide band gap transition metal dichalcogenides such as MoS2. To date, BP field-effect transistors have utilized a lateral geometry with in-plane transport dominating device characteristics. In contrast, we present here a vertical field-effect transistor geometry based on a graphene/BP van der Waals heterostructure. The resulting device characteristics include high on-state current densities (> 1600 A/cm2) and current on/off ratios exceeding 800 at low temperature. Two distinct charge transport mechanisms are identified, which are dominant for different regimes of temperature and gate voltage. In particular, the Schottky barrier between graphene and BP determines charge transport at high temperatures and positive gate voltages, whereas tunneling dominates at low temperatures and negative gate voltages. These results elucidate out-of-plane electronic transport in BP, and thus have implications for the design and operation of BP-based van der Waals heterostructures.