Determination of Carrier Polarity in Fowler-Nordheim Tunneling and Evidence of Fermi Level Pinning at the Hexagonal Boron Nitride / Metal Interface

TL;DR

This study reveals that Fermi level pinning occurs at the metal/h-BN interface and that hole tunneling dominates in Fowler-Nordheim tunneling through h-BN, providing insights for 2D heterostructure device design.

Contribution

It demonstrates the occurrence of Fermi level pinning at the metal/h-BN interface and establishes that hole F-N tunneling is a general characteristic across various metals.

Findings

Fermi level pinning at the metal/h-BN interface with a pinning factor of 0.30.

Hole F-N tunneling is the dominant carrier in h-BN, opposite to SiO2.

Fermi levels are pinned around 3.5 eV from the conduction band top across different metals.

Abstract

Hexagonal boron nitride (h-BN) is an important insulating substrate for two-dimensional (2D) heterostructure devices and possesses high dielectric strength comparable to SiO2. Here, we report two clear differences in their physical properties. The first one is the occurrence of Fermi level pinning at the metal/h-BN interface, unlike that at the metal/SiO2 interface. The second one is that the carrier of Fowler-Nordheim (F-N) tunneling through h-BN is a hole, which is opposite to an electron in the case of SiO2. These unique characteristics are verified by I-V measurements in the graphene/h-BN/metal heterostructure device with the aid of a numerical simulation, where the barrier height of graphene can be modulated by a back gate voltage owing to its low density of states. Furthermore, from a systematic investigation using a variety of metals, it is confirmed that the hole F-N tunneling current is a general characteristic because the Fermi levels of metals are pinned in the small energy range around ~3.5 eV from the top of the conduction band of h-BN, with a pinning factor of 0.30. The accurate energy band alignment at the h-BN/metal interface provides practical knowledge for 2D heterostructure devices.