Tunnel spectroscopy of localised electronic states in hexagonal boron nitride

M T Greenaway,O Makarovsky,A Patanè,L Eaves,Abhishek Misra ,T M Fromhold,Artem Mishchenko ,Kenji Watanabe ,Yu N Khanin ,Davit Ghazaryan ,A K Geǐm ,Vladimir I Fal’ko ,Matthew Holwill ,С В Морозов ,Kostya S Novoselov ,Yun Cao ,Е Е Вдовин ,Takashi Taniguchi ,John R Wallbank ,Zihao Wang

doi:10.1038/s42005-018-0097-1

Abstract

Hexagonal boron nitride is a large band gap layered crystal, frequently incorporated in van der Waals heterostructures as an insulating or tunnel barrier. Localised states with energies within its band gap can emit visible light, relevant to applications in nanophotonics and quantum information processing. However, they also give rise to conducting channels, which can induce electrical breakdown when a large voltage is applied. Here we use gated tunnel transistors to study resonant electron tunnelling through the localised states in few atomic-layer boron nitride barriers sandwiched between two monolayer graphene electrodes. The measurements are used to determine the energy, linewidth, tunnelling transmission probability, and depth within the barrier of more than 50 distinct localised states. A three-step process of electron percolation through two spatially separated localised states is also investigated.

Highlights

Hexagonal boron nitride is a large band gap layered crystal, frequently incorporated in van der Waals heterostructures as an insulating or tunnel barrier
Defect-related phenomena can impair the electrical properties of future devices based on hexagonal boron nitride (hBN) by inducing random telegraph noise and causing electrical breakdown of its insulating properties when a sufficiently strong electric field is applied[43,44]
We investigate how electrons tunnel resonantly between two monolayer graphene electrodes through localised states within an hBN barrier

Summary

Introduction

Hexagonal boron nitride is a large band gap layered crystal, frequently incorporated in van der Waals heterostructures as an insulating or tunnel barrier. We attribute each of the two strong peaks to the threshold of resonant tunnelling through the same localised state (state A) within the hBN barrier when its energy, EA, becomes aligned with one or other of the chemical potentials, μb or μt, of the bottom (b) or top (t) graphene layers.

Results

Conclusion