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

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.