Tunnel spectroscopy of localised electronic states in hexagonal boron nitride

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 atomiclayer 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.

Resonant tunnelling into the two-dimensional subbands of InSe layers

“…Here, the white lines highlight the shift and splitting of the narrow R-resonance. The emergence of this additional narrow feature in the transport characteristics of our devices is similar to recent observations of resonant electron tunneling through localized states due to defects in hBN 23 . The stronger dependence of R on V g (dV SD =dV g~− 0.05) compared to that of S n (dV SD =dV g~− 0.005) suggests that R arises from carrier tunneling into the states of a localized defect close to the bottom gate electrode.…”

“…We note that InSe has a much smaller band gap energy than that of hBN, which was previously used to realize TFETs 5,8,23 . The band alignment of InSe and hBN with respect to the Dirac points of graphene (or the conduction band of MLG) is also quite different; whereas the Dirac point lies almost in the middle of the band gap of hBN, it is positioned closer to the conduction band edge of InSe 25 .…”

Tunneling spectroscopy of localized states of WS2 barriers in vertical van der Waals heterostructures

“…2c), presumably sulfur or tungsten vacancies. Similar features in hexagonal boron nitride tun-neling barriers have been reported recently [10,[25][26][27]. Moreover, an increase in the number of the resonances with back-gate voltage is observed ( Fig.…”

“…Tunneling spectroscopy in van der Waals and other heterostructures is a powerful tool that can reveal unique information about the density of states (DOS) of the electrodes [1,2], about phonons (or other excitations) [3][4][5], about the chiral, valley [6] and spin states of the carriers [7,8] and their interactions [9]. Recently it was shown that the presence of defects in crystalline hexagonal boron nitride (h-BN) tunneling barriers can be detected in the tunneling spectra, which is dominated by Coulomb blockade effects [10,11].…”

Magnetoresistance in Co-hBN-NiFe Tunnel Junctions Enhanced by Resonant Tunneling through Single Defects in Ultrathin hBN Barriers

“…In our ~1 nm thick MTJ direct tunneling remains a major contribution, which explains the relatively modest enhancement of both the junction conductance and the MR. We note that it is not surprising that we observe only one resonant feature, even though one can expect a number of defects to be present in the hBN barrier. This is because a significant contribution of impurityassisted resonant tunneling can only be expected for optimum conditions: defects close to the center of the barrier and to the Fermi level [46]. Another promising route to amplify the relative contribution of the defects is by employing nanojunctions with a very small area: Here the effect on the MR is expected to be much larger and a single impurity may lead to the MR sign inversion [22,47], as was seen experimentally in Ni/NiO/Co junctions with < 0.01 µm 2 area [36].…”