Tunneling photo-thermoelectric effect in monolayer graphene/bilayer hexagonal boron nitride/bilayer graphene asymmetric van der Waals tunnel junctions

TL;DR

This paper demonstrates a tunneling photo-thermoelectric effect in a graphene/h-BN/graphene heterostructure, revealing a new out-of-plane thermoelectric phenomenon driven by cyclotron resonance under magnetic fields.

Contribution

It introduces the tunneling photo-thermoelectric effect in asymmetric van der Waals heterostructures and explores its dependence on magnetic field and Fermi energy.

Findings

TPTE voltage is generated under MIR irradiation and magnetic field.

TPTE signal peaks near the quantum Hall transition.

The effect depends on the Fermi energy tuning of monolayer graphene.

Abstract

Graphene is known to exhibit a pronounced photo-thermoelectric effect (PTE) in its in-plane carrier transport and attracting attention toward various optoelectronic applications. In this study, we demonstrate an out-of-plane PTE by utilizing electron tunneling across a barrier, namely, the tunneling photo-thermoelectric effect (TPTE). This was achieved in a monolayer graphene (MLG)/bilayer hexagonal boron nitride (h-BN)/bilayer graphene (BLG) asymmetric tunnel junction. MLG and BLG exhibit different cyclotron resonance (CR) optical absorption energies when their energies are Landau quantized under an out-of-plane magnetic field. We tuned the magnetic field under mid-infrared (MIR) irradiation to bring MLG into CR conditions, whereas BLG was not in CR. The CR absorption in the MLG generates an electron temperature difference between the MLG and BLG, and induces an out-of-plane TPTE voltage across the h-BN tunnel barrier. The TPTE exhibited a unique dependence on the Fermi energy of the MLG, which differed from that of the in-plane PTE of the MLG. The TPTE signal was large when the Fermi energy of the MLG was tuned near the phase transition between the quantum Hall state (QHS) and non-QHS, that is, the transition between carrier localization and delocalization. The TPTE provides another degree of freedom for probing the electronic and optoelectronic properties of two-dimensional material heterostructures.