Molecular Bridges Link Monolayers of Hexagonal Boron Nitride During Dielectric Breakdown

Alok Ranjan, Sean J. O’Shea, Andrea Padovani, Tong Su, Paolo La Torraca, Yee Sin Ang, Manveer Singh Munde, Chenhui Zhang, Xixiang Zhang, Michel Bosman, Nagarajan Raghavan, Kin Leong Pey

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

We use Conduction Atomic Force Microscopy (CAFM) to examine the soft breakdown of monocrystalline hexagonal boron nitride (h-BN) and relate the observations to the defect generation and dielectric degradation in the h-BN by charge transport simulations and density functional theory (DFT) calculations. A modified CAFM approach is adopted, whereby 500⨯500 nm2 to 3⨯3 µm2 sized metal/h-BN/metal capacitors are fabricated on 7 nm to 19 nm thick h-BN crystal flakes and the CAFM tip is placed on top of the capacitor as an electrical probe. Current-Voltage (I-V) sweeps and time dependent dielectric breakdown measurements indicate that defects are generated gradually over time, leading to a progressive increase in current prior to dielectric breakdown. Typical leakage currents are around 0.3 A/cm2 at 10 MV/cm applied field. DFT calculations indicate that many types of defects could be generated and contribute to the leakage current. However, three defects created from adjacent boron and nitrogen mono-vacancies exhibit the lowest formation energy. These three defects form molecular bridges between two adjacent h-BN layers, which in turn “electrically shorts” the two layers at the defect location. Electrical shorting between layers is manifested in charge transport simulations which show that the I-V data can only be correctly modelled by incorporating a decrease in effective electrical thickness of the h-BN as well as the usual increase in trap density which, alone, cannot explain the experimental data. An alternative breakdown mechanism, namely the physical removal of h-BN layers under soft breakdown, appears unlikely given the h-BN is mechanically confined by the electrodes and no change in AFM topography is observed after breakdown. High-resolution transmission electron microscope micrographs of the breakdown location show a highly localized (< 1 nm) breakdown path extending between the two electrodes, with the h-BN layers fractured and disrupted, but not removed.
Original languageEnglish (US)
JournalACS Applied Electronic Materials
StatePublished - 2023

Bibliographical note

KAUST Repository Item: Exported on 2023-01-30

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