Domain-wall/metal-electrode injection barrier in lithium niobate: Fowler-Nordheim tunneling fits best

The comprehensive description of both the electrical transport along conductive domain walls in lithium niobate single crystals and the charge injection at the interfacing metal electrodes, emerged to be a complex challenge. Recently, a heuristic evaluation allowed to postulate the “𝑅⁢2⁢𝐷⁢2 ” equivalent-circuit model (consisting of two parallel resistor-diode pairs) to appropriately match the dc current-voltage (I-V) characteristics. Here, we carefully revisit the interfacial electrical behavior, i.e., the diode part of the equivalent circuit model, since many more processes beyond the diode-related electron hopping transport (HT) assumed so far, may concurrently occur, such as thermionic emission (TE), Fowler-Nordheim tunneling (FNT), space-charge limited conduction (SCLC), and others. The “𝑅⁢2⁢𝐷⁢2 ” model thus needs to be generalized into an “𝑅⁢2⁢𝑋⁢2 ” circuit model (with 𝑋 = HT, TE, FNT, SCLC, and others) to fit to the experimental data. Moreover, to check for the best I-V curve fitting to the different theories, we apply a higher-harmonic DW current-contribution analysis, i.e., an ac I-V inspection, that allows us to discriminate between all these possible models with much higher precision than from pure dc I-V curve fitting. Both the ac and dc analysis yield consistent results, finding that the FNT model accounts best for the domain-wall/electrode junctions investigated here.